Date: Monday, January 6, 2014
Time: 8:00 am
Location: PHYS 401

TITLE:
A New Differential Absorption Lidar Using Raman Cells to Measure Subhourly Variation of Tropospheric Ozone Profiles in the Baltimore - Washington D.C. region

ABSTRACT:
This proposal will detail the theory and background necessary for the ground based tropospheric ozone Differential Absorption Lidar (DIAL) system at the NASA Goddard Space Flight Center (Greenbelt, MD 38.99° N, 76.84° W, 57 meters ASL), with initial results from 500 m to 10 km in Summer 2013. Current atmospheric satellites cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, NASA has funded the ground based Tropospheric Ozone Lidar Network (TOLNET) which currently consists of five stations across the US. The Goddard instrument is based on the Differential Absorption Lidar (DIAL) technique, which transmits three wavelengths, 266, 289 and 299 nm. Ozone is absorbed more strongly at 266 nm and 289 nm than at 299 nm. The DIAL technique exploits this difference between the returned backscatter signals to obtain the ozone number density as a function of altitude. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman Cells, filled with high pressure Hydrogen and Deuterium. Stimulated Raman Scattering within the focus shifts the pump wavelength and the first Stokes shift in each cell produces the required wavelengths. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range resolved number density can then be derived. A interesting scientific validation data set will be examined, which yields accurate initial results. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make continuous routine ozone profile measurements in the Washington, DC - Baltimore area.

Date: Thursday, December 12, 2013
Time: 1:00 pm
Location: PHYS 401

TITLE:
Shedding New Light on Accreting Pulsars

ABSTRACT:
Neutron stars are remnants of stellar evolution, the collapsed cores of massive stars. They are extremely dense and sustained against further gravitational collapse by neutron degeneracy pressure. Many have the strongest magnetic fields found in the universe. Accreting X-ray pulsars are rotating neutron stars which show regular flashes of X-ray emission powered by the accretion of material from a stellar companion onto the magnetic poles of the neutron star. The processes that take place at the poles involve strong gravitational fields, high temperatures and the most extreme magnetic fields. These are conditions that cannot take place naturally on Earth and cannot be reproduced in laboratories.

In recent years, considerable progress has been made regarding the development of physical models describing the accretion process onto the magnetic poles such that these new models can now be tested for the first time. These new models can now provide the first direct connection between physical parameters of the accretion process (magnetic field strength, plasma temperature, plasma density, mass accretion rate) and X-ray spectral shape. The standard empirical and new physical spectral models will be systematically applied to a sample of pulsars. Most of the chosen pulsars show a “cyclotron line”, a spectral feature that allows for a direct measurement of their magnetic fields. This detailed spectral analysis will be mainly based on observations from the Japanese X-ray satellite, Suzaku, due to its instruments’ high sensitivity, spectral resolution, and broad-band coverage. (The project will also include additional satellite data of a Symbiotic X-ray Binary, a member of a small, under-studied subclass of X-ray pulsars accreting from a dense stellar companion wind. Its study will involve modeling the spectrum as well as characterizing the variability and comparing the results with more common X-ray binaries.)

The goal of this project is provide the first steps towards a much needed improvement of our theories and observational analysis of magnetically dominated accretion, which can only be achieved by fitting the best physical models to the best available data.

Date: Wednesday, November 27, 2013
Time: 10:00 am
Location: PHYS 401

TITLE:
Study of the Relative Humidity Impact on Atmospheric Aerosols by Phase Function and Polarization Measurements Using the Polarized Imaging Nephelometer PI-Neph

ABSTRACT:
Atmospheric aerosols influence the Earth's radiation budget by scattering and absorbing sunlight radiation. Aerosols also modify the microphysical and radiative properties, as well as the water content and lifetime of clouds. In atmosphere conditions, aerosol particles experience hygroscopic growth due to the relative humidity (RH) influence. Wet aerosols particles are larger than their dry equivalents; therefore, they scatter more light. The quantitative knowledge of the RH effect on aerosols and its influence on the ability to scatter light is of substantial importance when comparing ground-based observations with other optical aerosol measurements techniques such satellite and photometry retrievals as well as for climate forcing calculations. This study focuses on measurements of aerosol optical properties under the effect of RH by performing different experiments where aerosols are humidified. Our next goal is to investigate the effect of water on aerosol phase function and polarized phase function using the UMBC Polarized Imaging Nephelometer (PI-Neph) designed and built by the LACO group. This study will produce the first reports of laboratory generated and ambient aerosol polarization measurements at high levels of RH.

Date: Monday, November 25, 2013
Time: 12:30 pm
Location: PHYS 401

TITLE:
New measurement scheme for second-order correlation measurements of thermal light

ABSTRACT:
Experiments using second order correlations have proven to be important for many applications, such as the Hanbury Brown Twiss interferometer which measures the angular size of stars, three dimensional LIDAR imaging, ghost imaging, quantum computing, and lithography. Of these experiments, only one regularly uses thermal light: the Hanbury Brown Twiss interferometer. The other experiments usually use lasers or entangled light sources, which are less than practical for many real-world applications. In addition, entangled experiments are typically performed at the single photon level and prone to decoherence. However, all of these experiments can also be performed with thermal light, such as sunlight, if one condition is met: the temporal coherence is increased allowing many measurements to be made within the coherence time. This is problematic for thermal light, as its temporal coherence is the inverse of its bandwidth, on the order of 10^-15. Our goal is to investigate the use of linear and nonlinear optics to stretch the time-scale of thermal light, reducing the bandwidth and increasing the temporal coherence without drastically reducing the intensity, allowing Hui Chen's Positive Negative Fluctuation Correlation Protocol to be used. This would result in a new method to achieve high intensity, high contrast second-order correlation measurements with broadband thermal light.

You're invited to attend Malachi's dissertation defense.

Date: Thursday, November 14, 2013
Time: 9:45 am
Location: PHYS 401

TITLE:
Examining the Role of the Compton-thick, X-ray reprocessor in Type 1 Active Galactic Nuclei

ABSTRACT:
Studies have indicated that black holes and their host galaxies must co-evolve, although the mechanism linking the two is not yet clear. X-ray observations of the actively accreting systems (active galactic nuclei, hereafter AGNs) over a valuable probe of conditions in the inner environs of the supermassive black hole, as X-ray production within these systems comprises a significant fraction (5%-40%) of the bolometric luminosity and originates close to the nucleus. Detailed spectroscopy in this bandpass has established that the inner environs comprise multiple X-ray absorbing zones with column densities extending into the Compton-thick regime (N_H > 10^24 atoms cm^-2). Compton-thick absorbers are known to have outflowing velocities up to 0.3c. The kinetic energy of oufltowing material with velocities > 0.1c may possibly be comparable to the gravitational binding energy of the stellar bulge and serve as a link between the black hole and the host galaxy. In addition, weak outflows may have a signicant effect on star formation in the host galaxy.

In this study, we use X-ray observations of radio-quiet AGN to examine some aspects of the flow of material between the black hole and the host galaxy. First, we model a small sample of unabsorbed Seyfert galaxies, finding their X-ray spectra to be consistent with arising as reflection from tens to hundreds of r_g in a Compton-thick, accretion disk wind of solar abundances seen face-on. Then, we explore properties of the local AGN population in the very hard band, above 10 keV, where there has been scant data available to date. We finnd a high flux for local AGN above 10 keV, and thus a very hard spectral shape over the Suzaku bandpass. Taken together, the spectral hardness and equivalent width of Fe K emission are consistent with reprocessing by an ensemble of Compton-thick clouds that partially cover the continuum source. Simple considerations place the distribution of Compton-thick clouds at or within 10^17 cm.

This work demonstrates not only that a Compton-thick wind can have a profound effect on the observed X-ray spectrum of an AGN, even when the system is not viewed through the flow, but that at least 50% of the continuum in type 1 AGNs is partially-covered by Compton-thick gas, suggesting that type 1 AGNs may not offer a completely direct view of the primary continuum, as once thought.

Date: Monday, November 11, 2013
Time: 2:00 pm
Location: PHYS 401

TITLE:
Investigation of Atomic Layer Deposition of Metal Oxides on III-V Semiconductors

ABSTRACT:
Atomic layer deposition (ALD) is becoming a leading technique for the fabrication of nanoscale materials because of its precise thickness control and unprecedented capability of film uniformity and surface conformality. Applications for such materials are diverse, ranging from Li-ion batteries and dye-sensitized solar cells to coatings on 3D structures and replacing SiO2 with high dielectric constant materials in metal oxide semiconductor field effect transistors (MOSFETs).

Our current understanding of ALD is based on ideal, one-pathway mechanisms. However, recent studies have shown we know very little about what reactions actually take place during ALD. The purpose of this research is to widen our understanding of the fundamentals of ALD by characterizing specific ALD processes such as the deposition Ta2O5 on InAs(100), post-deposition annealing effects on TiO2 thin films, the diffusion phenomenon of III-V semiconductor substrate atoms through metal oxide overlayers and explore the diffusion barrier capabilities of Al2O3 in these thin film systems.

Date: Monday, September 23, 2013
Time: 1:00 pm
Location: PHYS 401

Title
"Nonlinear Phase Shifts at Single-Photon Power Levels Using Tapered Optical Fibers in Rubidium Vapor"

Title
Our group has recently proposed a new form of macroscopic “phase-entangled” coherent state pulses with the potential to radically improve Quantum Communications (QC) systems. In contrast to conventional entangled pairs of single-photons which are highly susceptible to loss, these entangled pulses contain large numbers of photons and are predicted to propagate over long distances through lossy fiber channels. The key experimental requirement for generating these new entangled states is the realization of ultra-low power nonlinear phase shifts. Roughly speaking, what is needed is a robust Kerr-type nonlinearity in which the presence of a single-photon imparts a sizable phase shift on a macroscopic coherent state pulse.

Here I propose to experimentally demonstrate this nonlinear single-photon phase shift using a system comprised of a sub-wavelength diameter Tapered Optical Fiber (TOF) suspended in atomic rubidium (Rb) vapor. The proposed work leverages our group’s recent experience and experimental infrastructure in using the “TOF in Rb” system to demonstrate ultra-low power two-photon absorption. A successful demonstration of the proposed single-photon phase shifts would represent a significant advance in quantum optics, with a number of follow-on applications in QC.

Patricia successfully defended her dissertation on August 12, 2013.

TITLE:
Retrieval of optical and microphysical properties of aerosols from a hybrid lidar dataset

ABSTRACT:
Over the past decade the development of inversion techniques for the retrievals of aerosol microphysical properties (e.g. effective radius, volume and surface-area concentrations) and aerosol optical properties (e.g. complex index of refraction and single scattering albedo) from multiwavelength lidar system brought a new perspective in the study of the vertical distribution of aerosols. In this study retrievals of such parameters were obtained from a hybrid multiwavelength lidar dataset for the first time. In July of 2011, in the Baltimore-Washington DC region, synergistic profiling of optical and microphysical properties of aerosols with both airborne in-situ and ground-based remote sensing systems was performed during the first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar dataset combines elastic ground-based measurements at 355 nm with airborne High Spectral Resolution Lidar (HSRL) measurements at 532 nm and elastic measurements at 1064 nm that were obtained up to 5 km apart of each other. This was the first study in which optical and microphysical retrievals from lidar were obtained during the day and directly compared to AERONET and in-situ measurements. Good agreement was observed between lidar and AERONET retrievals. Larger discrepancies were observed between lidar retrievals and in-situ measurements obtained by the aircraft and aerosol hydration processes that were not taken into account in the study are believed to be the cause for the discrepancies observed.

Meimei successfully defended her dissertation on April 18, 2013.

TITLE:
Experiments Using Sub-Wavelength Diameter Tapered Optical Fibers in
Rubidium Vapor

ABSTRACT:
In this work, we describe experimental research on a relatively new
nonlinear optics system comprised of a sub-wavelength diameter Tapered
Optical Fiber (TOF) suspended in atomic Rubidium (Rb) vapor. The
compression of the evanescent optical mode propagating along the TOF
enables a dramatic increase in the nonlinear interactions between the
fields and the surrounding Rb atoms, thereby allowing the observation of a
variety of nonlinear optical effects with very low-power fields.
Specifically, we report on the observation of saturated absorption with nW
power levels and, more significantly, the observation of two-photon
absorption using power-levels corresponding to only 10’s to 100’s of
photons interacting with the Rb atoms at a given time.

One significant drawback to this "TOF in Rb" system is that at the
relatively high atomic densities needed for many of these experiments, Rb
atoms accumulating on the TOF surface can cause a significant loss of
overall transmission through the fiber. Here we report direct measurements
of the time-scale associated with this transmission degradation for various
Rb density conditions. We find that transmission is affected almost
immediately after the introduction of Rb vapor into the system, and
declines rapidly as the density is increased.

More significantly, we show how a heating element designed to raise the
TOF temperature can be used to reduce this transmission loss and
dramatically extend the effective TOF transmission lifetime. Our results
indicate that it is possible to achieve relatively high TOF transmission,
even in the presence of the relatively high Rb vapor densities that would
be needed for many low-power nonlinear optics applications. This study
represents a significant step in moving the basic "TOF in Rb" system from a
laboratory setting towards a practical ultra-low-power nonlinear optics
device.

Li successfully defended her dissertation on March 15, 2013.

TITLE:
Determination of the single scattering albedo and direct radiative forcing of biomass burning aerosol with data from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite instrument

ABSTRACT:
Biomass burning aerosols absorb and scatter solar radiation and therefore affect the energy balance of the Earth-atmosphere system. The single scattering albedo (SSA), the ratio of the scattering coefficient to the extinction coefficient, is an important parameter to describe the optical properties of aerosols and to determine the effect of aerosols on the energy balance of the planet and climate. Aerosol effects on radiation also depend strongly on surface albedo. Large uncertainties remain in current estimates of radiative impacts of biomass burning aerosols, due largely to the lack of reliable measurements of aerosol and surface properties. In this work we investigate how satellite measurements can be used to estimate the direct radiative forcing of biomass burning aerosols. We developed a method using the critical reflectance technique to retrieve SSA from the Moderate Resolution Imaging Spectroradiometer (MODIS) observed reflectance at the top of the atmosphere (TOA). We evaluated MODIS retrieved SSAs with AErosol RObotic NETwork (AERONET) retrievals and found good agreements within the published uncertainty of the AERONET retrievals. We then developed an algorithm, the MODIS Enhanced Vegetation Albedo (MEVA), to improve the representations of spectral variations of vegetation surface albedo based on MODIS observations at the discrete 0.67, 0.86, 0.47, 0.55, 1.24, 1.64, and 2.12 µm channels. This algorithm is validated using laboratory measurements of the different vegetation types from the Amazon region, data from the Johns Hopkins University (JHU) spectral library, and data from the U.S. Geological Survey (USGS) digital spectral library. We show that the MEVA method can improve the accuracy of flux and aerosol forcing calculations at the TOA compared to more traditional interpolated approaches. Lastly, we combine the MODIS retrieved biomass burning aerosol SSA and the surface albedo spectrum determined from the MEVA technique to calculate TOA flux and aerosol direct radiative forcing over the Amazon region and compare it with Clouds and the Earth's Radiant Energy System (CERES) satellite results. The results show that MODIS based forcing calculations present similar averaged results compared to CERES, but MODIS shows greater spatial variation of aerosol forcing than CERES. Possible reasons for these differences are explored and discussed in this work. Potential future research based on these results is discussed as well.

Date: Wednesday, January 9, 2013
Time: 2:00 pm
Location: PHYS 401

Title
Improving estimates of CO emissions from biomass burning using FRP and its applicability to atmospheric models.

Abstract
Biomass burning is responsible for the second largest source of Carbon emissions that include Carbon Dioxide (CO2), Carbon Monoxide (CO), and Methane (CH4) emissions. Despite the necessity of quantifying these emissions, a reliable and an efficient approach is unavailable. Hence, we are proposing a new approach, with the focus on CO, a trace gas where the remote sensing is well established and generated from a variety of satellite sensors. For comparison and validation purposes, ARCTAS field campaign is selected.

Despite the multi-sensor capability of several satellites, such as the Terra satellite that we are using at the primary stage of the analysis: MOPITT sensor to obtain CO data, MISR sensor for smoke plume height and MODIS sensor for FRP, there still remains constraints to be addressed. For example, MOPITT sensor is primarily sensitive only to the mid-troposphere so it is not capable of retrieving CO near the fire origin. However, when these high concentrations travel downwind and reach the altitude threshold sensitive to MOPITT, it is detectable by the MOPITT sensor. Throughout the transport, these CO fields move with visible smoke plumes detected by MISR. So, MODIS detected fire locations are connected to MISR detected smoke plumes, which in turn connected to MOPITT detected CO fields.

In applying the above methodology, GEOS-5 wind data will be used with WRF-Chem model to produce the forward transport and to link CO emissions from their sources to the current atmospheric distributions. Then to get the emission time frames, HYSPLITT back-trajectory analysis will be used. To validate the products, airborne measurements will be used with CO data from AQUA AIRS and AURA TES.

Date: Thursday, December 6, 2012
Time: 10:00am
Location: PHYS 401

Title
Developing and Characterizing X-ray Concentrators for Astronomical Observations and X-ray Polarization

Abstract
Advancements in technology have caused a dramatic increase in the number of cosmic X-ray sources discovered and over the past half century. Dramatic increases in the sensitivity, and in the spatial, spectral, and temporal resolution of these instruments have led to numerous advances in our understanding of the physical conditions in almost every class of astronomical object. Several classes of such objects (such as neutron stars and supernova remnants) contain strong magnetic fields leading to a substantial fraction of the X-ray emission suspected of being polarized. Studies of polarized X-rays will therefore open up a new dimension in discovery space and help further constraint our models for these sources.

Unfortunately to date there have been minimal studies on X-ray polarization due to the lack of dedicated X-ray polarimeters on big missions. I am working with the X-ray advanced Concepts Testbed (XACT) sounding rocket project which will be launched next year to observe the Crab Nebula. The goal is to test the new technologies specifically designed to advance this field, specifically high throughout X-ray concentrators and a time projected gas chamber polarimeter. The Neutron star Interior Composition ExploreR (NICER) shares some of the same technology, yet for other scientific goals. I am working to develop a method to characterize and calibrate the technology with the instrument development teams. I will give a brief overview of the projects, explain the work I have completed so far, and describe the work planned for the remainder of my thesis.

Congratulations to the 10 Physics Graduate Students who advanced into PhD Candidacy during the past year:

Brian Kirby (advisor: Dr. Franson)
Erika Nesvold (advisor: Dr. Georganopoulos)
Liwang Ye (advisor: Dr. Gougousi)
Hong Cai (advisor: Dr. Johnson)
Joel Coley (advisor: Dr. Henriksen)
Amanda Dotson (advisor: Dr. Georganopoulos)
Neetika Sharma (advisor: Dr. George)
Patricia Sawamura (advisor: Dr. Hoff)
Adriana Lima (advisor: Dr. Martins)
Barry Baker (advisor: Dr. Sparling)

These students were recognized at the Graduate School's annual Doctoral Candidates Reception on November 1, 2012. Pictured at the reception are (l to r): Dr. Lynn Sparling, Dr. James Franson, Dr. J. Vanderlei Martins, Adriana Lima, Brian Kirby, Barry Baker, Joel Coley, Dr. Mark Henriksen.

Date: Thursday, September 6, 2012
Time: 10:00am
Location: PHYS 401

Title
Physical Processes Influencing the Mid-Atlantic Planetary Boundary Layer with Applications in Air Quality and Wind Energy

Abstract
Understanding the Planetary Boundary Layer (PBL) dynamics is essential in air quality, wind energy and numerical weather prediction, specifically the vertical mixing processes of heat, momentum and constituents. Currently, it is suggested to be the most important factor in modeling the lower atmosphere especially in regions of complex terrain such as the Mid-Atlantic region. In this proposal an synergy of measurements and models will be used to investigate vertical mixing processes in the Mid-Atlantic region. The utilization of a baroclinic zone as a wind resource in the Mid-Atlantic region will be analyzed by use of high resolution model runs in comparison with wind, aerosol, and other measurements. These model and data analysis aim to improve the current understanding of turbulent mixing in the complex terrain of the Mid-Atlantic Region.

Date: Wednesday, September 5, 2012
Time: 9:30am
Location: PHYS 401

Title
Optical, microphysical and compositional properties of volcanic ash, soil dust, urban pollution and other aerosols.

Abstract
The microphysical properties of aerosols are of fundamental importance in the estimation and prediction of their direct and indirect forcing effects on the balance of energy of the Earth. One of the main parameters missing in current atmospheric models is the complex refractive index of aerosol particles from the ultraviolet (UV) to the short-wave infrared (SWIR) wavelength. The main objective of this project is to perform a detailed characterization of important optical and microphysical properties of aerosol particles, and create a database for these commonly missing parameters. This research proposes to investigate the geometrical size distribution, shape, material density, and imaginary part of the refractive index of different types of aerosols from UV to SWIR wavelengths. The proposed methodology includes in situ measurements using the LACO-UMBC Reflec-Nephelometer, and aerosol in situ filter collection using the LACO Aerosol Sampling Stations. Also, materials can be collected directly from the ground (like deposited volcanic ash, or dust) and brought to our laboratory for posterior re-suspension. Our experimental setup allows us to separate particles into PM10, PM2.5, or PM1.0. Particles collected on filters are analyzed by different techniques, such as Scanning Electron Microscopy (SEM) for determination of size distribution, reflectance measurements for determination of the optical absorption properties as a function of the wavelength, and Proton Induced X-ray Emission (PIXE) or X-Ray fluorescence for elemental composition. Finally, the spectral imaginary part of refractive index (from 300 to 2500nm) is derived numerically from the measurements of mass absorption coefficient, size distribution and geometrical shape of the particles, and the density of the material. The selected samples for this study include materials collected at vicinity of volcanic eruptions at Eyjafjallajökull (Iceland), Puyehue (Chile), Mont Saint Helens and Fuego Volcano (USA), dust from central Sahara at Birmoghrein (Mauritania) and Bordj Mokhtar (Algeria), and urban pollution with distinct organic and black carbon components.

Date: Friday, August 24, 2012
Time: 10:00am
Location: PHYS 401

Title
Phase Entanglement With Macroscopic Coherent States

Abstract
Entanglement is one of the defining features of quantum mechanics, with current applications in communications and cryptography, but with a wide range of possible future technologies such as quantum computing. Most entanglement experiments use single photons as the carriers of entanglement, and are therefore limited in distance because of the effects of absorption. Entanglement in macroscopic systems such as coherent states with large amplitudes has been suggested in terms of Schrodinger cat states, but rely on large nonlinearities making them unrealistic. In this proposal a method for performing nonlocal interferometry with entangled macroscopic coherent states created using weak nonlinearities is described. In addition an accompanying quantum key distribution scheme is outlined. An analysis of the effects of loss on such a system shows that a large number of photons can be absorbed from the coherent states with only a small loss in visibility. This result along with an entanglement swapping method may allow for greatly improved distances for quantum communications than currently possible.

Congratulations go to the following Physics undergraduate students for receiving the Outstanding Undergraduate Learning Assistant Award!

Fall 2011 - Matthew Wilcox
Spring 2012 - Matthew Davis

This award acknowledges and recognizes the best Learning Assistant for his/her work as instructor in the classroom and laboratory. Each award recipient will receive:

• An award plaque presented at the first Physics Colloquium in the following semester.
• $300 cash award.
• Recognition at the annual College of Natural and Mathematical Sciences Student Recognition Day.
• Letter of congratulation from the American Association of Physics Teachers (AAPT) and one‐year gift membership (including access to its electronic journals ‐ the American Journal of Physics and The Physics Teacher).

Congratulations go to the following Physics graduate students for receiving the Outstanding Graduate Teaching Assistant Award!

Fall 2011 - Fernando Calderon Vargas
Spring 2012 - Garrett Hickman

This award acknowledges and recognizes the best Graduate Teaching Assistant for his/her work as instructor in the classroom and laboratory. Each award recipient will receive:

• An award plaque presented at the first Physics Colloquium in the following semester.
• $500 cash award.
• Recognition at the annual College of Natural and Mathematical Sciences Student Recognition Day.
• Letter of congratulation from the American Association of Physics Teachers (AAPT) and one‐year gift membership (including access to its electronic journals ‐ the American Journal of Physics and The Physics Teacher).

From left to right: Soutry De, Lauren Woods, Ingrid Venero-Velez, Timothy Pillsbury

The Fifteenth Annual UMBC Summer Undergraduate Research Fest hosted by the College of Natural and Mathematical Sciences (CNMS) was held on Wednesday, August 8, 2012 on the Seventh Floor of the Albin O. Kuhn Library.  This event serves as a culminating activity for many students in grant-funded and other formal summer undergraduate research programs that are connected to UMBC and our College.  At the event, the young researchers gave oral or poster presentations of their summer research to the UMBC community.

UMBC fellow makes breakthrough in 'ghost imaging'
Quantum camera a sophisticated new way of taking pictures

Sanjit Karmakar, a post-doctoral physics fellow at UMBC is doing research in "ghost imaging" using a quantum camera and sunlight
July 13, 2012 | By Jonathan Pitts, The Baltimore Sun

Visit the campus of the University of Maryland, Baltimore County on any cloudless afternoon, and you're likely to happen on an intriguing sight: a slender fellow bent over a contraption that looks like a cross between an 1890s camera and a bulky steamer trunk.

That would be Sanjit Karmakar, a post-doctoral physics fellow who's using his "magic box" to take pictures by following the sun across the sky. One day, the pictures will be of objects thousands of miles away.

TO READ ARTICLE IN ITS ENTIRETY –
http://www.baltimoresun.com/health/maryland-health/bs-hs-physics-ghost-imaging-20120713,0,1108375.story

Dr. Raymond Hoff has been awarded the 2012 NASA Distinguished Public Service Medal.

This is NASA's highest form of recognition that is awarded to a Government employee who, by distinguished service, ability, or vision has personally contributed to NASA's advancement of United States' interests. The individual's achievement or contribution must demonstrate a level of excellence that has made a profound or indelible impact on NASA mission success, and therefore, the contribution is so extraordinary that other forms of recognition by NASA would be inadequate.

The entire ceremony can be watched on NASA's YouTube channel. Introduction to the Distinguished Service Medals starts at 28:00 minutes.
http://www.youtube.com/watch?v=nA3rOlwOfzY&feature=BFa&list=UULA_DiR1FfKNvjuUpBHmylQ

Junlin successfully defended her PhD dissertation on May 15, 2012.

TITLE:
An Experimental Study of Nonclassical Effects in Two-photon Interferometry

ABSTRACT:
Two-photon interferometry is a relatively new field with applications ranging from precise measurements of optical phase shifts to fundamental tests of quantum mechanics. In contrast to conventional single-photon interferometry, two-photon interferometry typically involves measuring correlations between two detectors placed in two output ports of an interferometer. Of particular interest is two-photon interferometry with entangled photon pairs, in which case it is often possible to observe effects that are not possible with classical fields. Because these entanglement effects are becoming increasingly important in Quantum Information Processing (QIP) applications, there is currently a strong need for further exploration of new ideas, basic physics, and experimental techniques of two-photon interferometry.

In this defense, I will report the results of three new two-photon interferometry experiments using entangled photon pairs produced by a Type-I Parametric Down-Conversion (PDC) source. In the first experiment, we demonstrate a new technique for compensating for two-photon interferometer beamsplitter asymmetries by manipulating the polarization degree of freedom in the system. Roughly speaking, projective polarization measurements are used to re-balance the magnitude of various two-photon amplitudes that were made distinguishable by non-ideal refection and transmission coefficients of a key beamsplitter. In the second experiment, we utilize a short coherence-length continuous-wave (CW) PDC pump laser to explore two-photon interferometry in a new intermediate regime between the more familiar extremal cases which use either a long coherence-length CW pump or an ultra-short pulsed pump laser. These results provide new insight into the role of PDC pump coherence in two-photon interferometry. Finally, we use two-photon interferometry to experimentally investigate "entangled photon holes", which is a new form of entanglement that arises from the correlated absence of photon pairs in an otherwise constant background. By using vastly unbalanced interferometers and well-defined timing, we observe nonclassical correlations due to "time-bin" entangled photon-hole states.

Date: Monday, April 30, 2012
Time: 3:00pm
Location: PHYS 401

Title
Optical Measurement on Quantum Cascade Lasers and Mid-IR Semiconductor Materials Using Femtosecond Pulses

Abstract
Ultrafast time-resolved optical technique provides an insight into the carrier dynamics and light-matter interactions in quantum cascade lasers (QCLs) and mid-IR semiconductor materials. The proposed research will use the mid-infrared (mid-IR) fs pulses from a difference frequency generator (DFG) to investigate the carrier dynamics and nonlinearities of QCLs provided by Princeton University, grown by metal-organic chemical vapor deposition (MOCVD). Additionally, fs near and mid-IR pulses are used to excite photoluminescence (PL) to investigate the quality of novel mid-IR semiconductor materials.

QCLs are unipolar devices based on intersubband transitions instead of interband transitions as in most semiconductor lasers. To investigate their carrier dynamics such as resonant tunneling, stimulated emission, and superlattice transport, we need to eliminate electron-hole generation, light and heavy-hole effects, and other interband processes. fs mid-IR pulses provide the resonant photon energy for pump-probe techniques in QCLs. In the pump-probe technique, a strong pump beam is coupled into the active core of a working QCL to perturb the population inversion and the gain from equilibrium. A weak probe beam is used to monitor the gain recovery after the carrier distribution is perturbed by the pump. The dependence of the probe signal on the time delay between the pump and probe gives the time-resolved information on the intersubband transition related carrier mechanisms mentioned above. The pump-probe signal indicates the dephasing mechanisms such as electron-electron (e-e) scattering, electron longitudinal optical (LO) phonon scattering, and carrier heating etc., decreasing the intersubband tunneling rate. Among all the dephasing mechanisms, the LO phonon scattering plays a dominant role in QCLs. This proposed research will apply pump-probe technique in QCLs at different temperatures, because the phonons are largely suppressed at cryogenic temperatures. In addition, QCLs have giant inherent nonlinearities, which give the QCLs a potential in ultrafast pulse generation. The Kerr nonlinearities will be studied by coupling the mid-IR fs pulses into a QCL waveguide.

The second part of this research is to investigate novel mid-IR semiconductor materials using fs pulse excited photoluminescence (PL) and time-resolved photoluminescence (TRPL). Preliminary experimental measurements have been conducted on an InAs/GaSb type-II superlattice sample grown by MOCVD at UMBC.

The results of this research will provide a better understanding of carrier dynamics in QCLs and novel mid-IR materials and would further help the designers and growers to improve the quality and performance of mid-IR devices.

Date: Wednesday, April 25, 2012
Time: 11:00 am
Location: PHYS 401

TITLE:
Probing the Structure and Morphology of X-ray and Gamma Ray Binaries

ABSTRACT:
High Energy Binary Systems, consisting of a stellar remnant and a companion object, are best characterized by the mass of the companion star and the energy band of the emission (X-ray or gamma ray). The mass transfer mechanism present in High Energy Binary Systems is dependent on the companion’s mass (high mass or low mass in relation to the compact object) and the orbital separation between the two objects. Temporal and spectral data indicate that High Energy Binary Systems show various absorption and emission features that require further research to probe into the mass transfer mechanism, observed luminosity outbursts and other physical properties of the system. I plan to develop a case study of these systems using a detailed temporal and spectral analysis of the poorly understood 4U 1210-64 in addition to archived data on other elusive sources. These data have been and will be collected using the Suzaku and Fermi Space Telescopes. The objective of our research is to understand the mass transfer mechanism present in these systems, characterize the physical properties of the X-ray and gamma ray emission and to further understand the relationship between the orbital period and spin period of these objects (Corbet’s diagram).

Date: Tuesday, April 24, 2012
Time: 10:00 am
Location: PHYS 401

TITLE:
Surface reactions during the atomic layer deposition of high‑κ dielectrics on GaAs surfaces

ABSTRACT:
Atomic layer deposition (ALD) of high dielectric constant (high‑κ) gate dielectrics on III-V semiconductors has been a subject of great interest and has shown promising applications in metal-oxide-semiconductor field effect transistors (MOSFET). However, the mechanism for the deposition of high‑κ gate dielectrics on III-V semiconductors is still not clear. The purpose of the proposed research is to study the surface reactions of a series of metal organic precursors and H₂O on GaAs surfaces during ALD. The adsorption and reaction of HfO₂ precursors, including tetrakis(dimethylamino)hafnium [Hf(N(CH₃)₂)₄] (TDMAH), tetrakis(diethylamino)hafnium [Hf(N(C₂H₅)₂)₄] (TDEAH) and tetrakis(ethylmethylamino)hafnium [Hf(N(CH₃C₂H₅)₄] (TEMAH), TiO₂ precursor tetrakis(dimethylamino)titanium [Ti(N(CH₃)₂)₄] (TDMAT) and Ta₂O₅ precursor pentakis(dimethylamino)tantalum [Ta(N(CH₃)₂)₅] (PDMAT) and H₂O on GaAs (100) surfaces will be investigated by in-situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). This research will improve our understanding of the surface reaction mechanisms during the ALD of high‑κ gate dielectrics on III-V semiconductors.

Date: Thursday, April 19, 2012
Time: 8:00 am
Location: PHYS 401

TITLE:
Retrieval of microphysical properties of aerosols from a hybrid multiwavelength lidar dataset

ABSTRACT:
Aerosols continue to pose one of the largest uncertainties in the global models utilized to assess different climate change scenarios. In particular, models still fail to represent the vertical distribution of aerosols in the atmosphere with reasonable accuracy.

Currently, most aerosol measurements and retrievals from either spaceborne or ground-based instruments reflect the contribution of the total atmospheric column and therefore do not provide information on the aerosol vertical distribution. Lidar (light detection and ranging) systems are of particular interest in that respect, as they are able to provide profiles of optical properties of aerosols, such as backscatter and extinction coefficients, with high spatial and temporal resolution. Furthermore, it has been demonstrated that from backscatter and extinction coefficient profiles at multiple wavelengths it is possible to retrieve physical properties of aerosols such as effective radius, surface-area, number and volume distributions, complex index of refraction and single scattering albedo.

Most studies to test and validate the inversion algorithm scheme for multiwavelength lidar data have been restricted to the combination of the elastic and Raman scattering measurements from ground-based systems that were carefully designed to emit and receive signals in the same optical path. For this work I propose a new combination of lidar measurements, comprising airborne HSRL (High Spectral Resolution Lidar at 532 nm + 1064 nm elastic channel - nadir viewing) and ground-based elastic and Raman measurements (at 355 nm - zenith viewing). In this new geometry, HSRL measurements within 5 km of the ground-based systems are regarded as collocated measurements. By combining different lidar retrieval techniques to obtain the optical dataset at multiple wavelengths necessary to retrieve the aerosol microphysical properties, and by adding a horizontally averaged component from the geometry of the problem, I will be exploring the feasibility of utilizing this new methodology for test and validation of the retrieval algorithms in the framework of future field campaigns employing synergistic airborne and ground-based lidar measurements, and also for a future spaceborne multiwavelength lidar mission.

Jaime successfully defended his Masters thesis on April 18, 2012.

TITLE:
Determination of Planetary Boundary Layer Height from Ground Based Wind Profiler and Lidar Measurements using the Covariance Wavelet Transform (CWT)

ABSTRACT:
This thesis documents the application of the Covariance Wavelet Transform (CWT) to lidar and, for the first time to our knowledge, wind profiler data to examine the possibility of accurate and continuous planetary boundary layer height (PBLH) measurements on short temporal resolution (one and fifteen minute averages respectively). Comparisons between PBLHs derived from the Elastic Lidar Facility (ELF) through application of the CWT and daytime radiosonde launches from Beltsville and RFK Stadium as part of the September 2009 NOAA/ARL and NCEP field study show an R2 = 0.84 correlation. PBLHs from ELF aided in diagnosing issues with the automatic PBLH calculation from Aircraft Communications Addressing and Reporting System (ACARS) profiles in the Real-Time Mesoscale Analysis used by plume dispersion modelers.

The lowest two kilometers of the atmosphere are only probed infrequently in time and sparsely in the United States. In particular, the 00Z and 12Z launches of radiosondes are particularly ill-posed to obtain PBLH mixing, and depth at the peak of the heating cycle in the daytime. This is reflected by comparisons between PBLHs from ELF and PBLHs from radiosonde launches from Dulles International Airport and Aberdeen Proving Ground at 00 and 12Z which show a R2 = 0.39 correlation.

Determining the mixing in the PBL was one goal of a study of the spatial and diurnal variations of the PBL height over Maryland for July 2011, during NASA’s Earth Venture mission DISCOVER-AQ. A semi-automated PBLH detection algorithm utilizing the CWT for wind profiler data was developed. This algorithm was tested on data from the 915 MHz wind profiler at Beltsville, Maryland, and compared against PBLHs derived from ground based radiosondes measured at Beltsville. Comparisons were also done between PBLHs derived from ground based lidars at UMBC and Beltsville. Results from the comparison show an R2 = 0.87, 0.89, and 0.91 correlation between the radiosonde PBLHs and the lidars and wind profiler PBLHs, respectively.

Accurate determination of the PBLH by applying the CWT to lidar and wind profilers will allow for improved air quality forecasting and understanding of regional pollution dynamics.

Neetika successfully defended her PhD Proposal on February 8, 2012.

TITLE:
Diagnostics of Photoionized Gas in Seyfert Galaxies

ABSTRACT:
As their name implies Active Galactic Nuclei (AGN) reside in the centers of many (10%) galaxies. They are active in the sense that their spectra exhibit a broad (from radio to gamma-rays) non-stellar continuum which exceeds the luminosity of the host galaxy. Furthermore at some wavelengths intensity variations have been observed on timescales less than a day (minutes in extreme cases). The ultimate cause of this tremendous outflow of energy in the form of radiation is widely believed to be due to the accretion of matter onto a supermassive black hole (BH ~ 10⁶-10⁹ times the mass of the Sun). Unfortunately since all this activity takes place in such a relatively small region (<< 3lyr) the central engine of even the closest AGN cannot be imaged directly with current technology (eg. The central region of Circinus, the nearest active galaxy at a distance of about 40 million trillion miles, has an angular size of about 0.2" that is just resolvable with VLT of spatial resolution 0.1"-0.5" ). Nevertheless spectroscopic observations can help us constrain the conditions of the gas very close to the BH. Such observations reveal that, as expected from considerations of the angular momentum of the infalling matter, such material in the circumnuclear regions of an AGN is not in a spherically-symmetric distribution. The unified model of AGN comprises of different gas components surrounding the central engine and hence that leads to the classification of AGN depending upon their oreintations with respect to the observer on the Earth.

My thesis focuses on constraining the physical conditions in the NLR of Seyfert galaxies. I propose to compare observational data with the predictions of a publically available software tool CLOUDY in order to further constrain the conditions within the circumnuclear regions of a number of nearby Seyfert Galaxies. Specifically I propose to use archival data in the soft X-ray band (6-38Å) obtained by the grating spectrometers onboard the XMM-Newton and Chandra observatories for this purpose. Some Seyfert galaxies (Seyfert 2 galaxies) emit a multitude of emission lines due to H-like and He-like ions of the cosmically abundant elements (C, N, O, Ne, Mg...etc). These line intensities are far in excess of those predicted by models of the gas in the standard Unied Model of Active Galactic Nuclei (AGN). It has been suggested that the lines are due to an additional amount of circumnuclear material. Some of this material is actually thought be co-located with the so-called Narrow-line region (NLR) of AGN. This has been dubbed the Xray NLR (XNLR) and is probably co-located with the regular NLR. Due to the intense continuum radiation, the XNLR gas is thought to be photoionized. Understanding this X-ray emitting component of gas is important, as it will help us understand the overall structure and dynamics of the circumnuclear regions of AGN.

Sanjit successfully defended his PhD dissertation on February 1, 2012.

TITLE:
Ghost Imaging with Sunlight

ABSTRACT:
The main result of this dissertation is the first successful experimental demonstration of ghost imaging using the sun as a light source. This result supports the quantum theory of near-field thermal light ghost imaging and also clarifes the physics of near-field thermal light ghost imaging from the fundamental level. The quantum theory of two-photon interference is the key to understanding non-local ghost imaging with thermal light sources. Two-photon interference occurs between two different yet indistinguishable probability two-photon amplitudes, nonclassical entities produced by the joint-detection between two distant photo-detectors. On the other hand, the classical theory considers the reason behind thermal light ghost imaging to be an intensity fluctuation correlation. Interestingly, the physics of intensity fluctuation correlation was misled by the speckle-to-speckle picture.

The experimental demonstration of ghost imaging with sunlight suggests that the nonlocal ghost-imaging effect of thermal light is caused by quantum-mechanical two-photon interference and it also proves that the idea of 'speckles" is unnecessary in near-field thermal light ghost imaging. Most importantly, the sun does not make any speckle and it is a near-field source. The experimental studies on sunlight-based ghost imaging is discussed in two steps: (1) an experimental demonstration as well as a quantum mechanical explanation of the nontrivial intensity correlation with the sun, a natural thermal source, as a light source and (2) the demonstration of the experimental observation of ghost imaging with sunlight with its quantum-mechanical explanation. These observations with their theoretical explanation are very helpful to understanding the physics of ghost imaging from a fundamental level. From the application point of view, sunlight-based ghost imaging may achieve a spatial resolution equivalent to that of a classical imaging system taking pictures at a distance of 10 km with a lens of 92 m size.

So far ghost imaging using thermal light with one color are demonstrated. This dissertation also reports an experimental study of two-color, biphoton ghost imaging using an entangled photon pair source. The result of this experimental observation shows a ghost image with enhanced angular resolving power by means of a greater field of view compared with that of classical imaging. The experience gained in the two-color ghost imaging experiment with entangled photon pairs will be helpful to get a real color ghost image with sunlight. A proposal to achieve sunlight-based ghost imaging with real colors is also reported here. Potential real color sunlight-based ghost imaging with its nonlocal behavior and turbulence-free nature gives us a promise for its applications in distant imaging.

Chris successfully defended his PhD dissertation on November 29, 2011.

TITLE:
Multivariate Retrieval of Carbon Monoxide

ABSTRACT:
A new technique is presented here to retrieve carbon monoxide (CO) profiles from Atmospheric Emitted Radiance Interferometer (AERI) spectra. This retrieval version deviates from the previous AERI CO retrieval method, which utilized signal processing to determine a constant CO mixing ratio representative of the entire troposphere. Instead, this retrieval version utilizes linear mapping to ascertain an estimate of the CO profile. A detailed analysis is conducted to estimate the error from all aspects of the the linear mapping procedure including measurements, forward modeling of atmospheric radiation, and uncertainty from inputs to the forward model. It was found that the dominant sources of error were from cloud contaminated spectra and uncertainty in absorption line strengths inside the forward model, A new cloud flagging technique that uses a neural network to identify spectra affected by clouds was tested and compared to the previously used version based on brightness temperature contrast. The neural network method decreased uncertainty between AERI and forward model spectra by 30 percent when compared with the previously used version.

First guess CO profiles to the AERI retrieval were from two different sources. One source was an a priori CO profile calculated as the mean profile from 56 individual measurements where each CO profile encompasses tower, aircraft, and satellite CO measurements. The other first guess CO profile came from the AIRS version 5 (AIRSv5) retrieved CO product. Incorporating the AIRS CO profile to the AERI retrieval provided a better estimate of free tropospheric CO when compared with the a priori profile. Using a better upper tropospheric CO estimate resulted in more accurate results from the AERI retrieval below 2 km, thus revealing that an AERI plus AIRS retrieved CO product is superior to either instrument's own CO retrieval working alone. The combined retrieval product is shown to have an RMSE of 10% in the first 2 km of the atmosphere.

Erika successfully defended her PhD Proposal on November 21, 2011.

TITLE:
A Collisional Algorithm for Modeling Debris Disks

ABSTRACT:
Many stars harbor disks of debris, in the form of dust and planetesimals, left over from planet formation. Any planets orbiting in these debris disks will gravitationally perturb the planetesimals, creating morphological features in the disk. These features have a large angular extent on the sky compared to planets, and can be more easily resolved than the planets themselves. We can therefore use images of a resolved debris disk to predict the presence of a perturbing planet and constrain its mass and orbital elements, even when the planet is too faint to be observed.

But to use this planet-finding technique, we need accurate models of the evolution of the disk as it is shaped by the planet. This problem has previously been addressed using N-body integrators to simulate the dynamics of a planet-disk system, but these models neglect or over-approximate the effects of catastrophic collisions between planetesimals. Such collisions affect the dynamics of the planetesimals as well as their size distribution as the kinetic energy of the colliding planetesimals is used to shatter them into smaller fragments.

I propose to develop a debris disk model that combines an N-body integrator to solve the equations of motion for the planetesimals and planets in a disk and a collisional algo- rithm to correct the trajectories of colliding planetesimals and calculate the evolution of the planetesimal size distribution as fragments are created. My model will take as its inputs various parameters such as planetary and stellar mass, the planets’ initial orbital elements, and the initial distribution of planetesimals. The output of my model will be simulated images of the evolved disk. After the model has been completed and tested, I will apply it to archived data of several different resolved debris disks to constrain the mass and orbital elements of confirmed planets and to predict the presence, mass, and orbits of undetected planets.

Debra successfully defended her PhD dissertation on November 10, 2011.

TITLE:
The Impact of Upper Tropospheric Dynamics on Surface Air Quality over the United States
ABSTRACT:

Monitoring air quality and source attribution at the surface requires a vast understanding of radiative and dynamical effects in the lower atmosphere to capture influential processes affecting human health, the environment, and current pollutant standards. In order to accurately determine all sources impacting lower atmospheric composition, a more thorough comprehension of the dynamical, chemical, and radiative coupling of the stratosphere and troposphere is required. Particularly significant is the transport or exchange of trace gases, both natural and anthropogenic, between the stratosphere and troposphere also known as stratosphere-troposphere exchange (STE). During previous research campaigns, STE was found to contribute to the tropospheric ozone budget. In this work, a plan was designed to determine whether or not stratosphere-to-troposphere transport (STT) was a viable mechanism for elevated ozone at the surface, particularly in cases where unhealthy air quality conditions were detected.

An investigation of several case studies in which high levels of surface ozone appear to originate from the stratosphere shows that a variety of dynamical processes from the boundary layer to the lower stratosphere are involved. Starting with the quasigeostrophic equations of vertical and horizontal motion, dynamical parameters can be derived and evaluated from the North American Regional Reanalysis (NARR) meteorological fields. Reanalysis diagnostics, such as Q-vector, can locate the prevailing STT mechanism and capture the extent of vertical transport and mixing into the lower troposphere. Back trajectories from the University of Maryland Baltimore County - Lagrangian Trajectory (UMBC-LT) model released at the ground sites present additional support.

Along with the reanalysis dataset, a combination of satellite-retrieved and surface observations of chemical tracers were utilized to demonstrate the plausibility of a stratospheric source and to rule out anthropogenic surface contributions where possible. The practicality of Atmospheric InfraRed Sounder (AIRS), Tropospheric Emission Spectrometer (TES), and High Resolution Dynamics Limb Sounder (HIRDLS) satellite observations to infer stratospheric transport as the probable source was tested for these case studies and the results supported dynamical evidence of STE using tracer correlations, as in the ozone-water vapor relationship. The overall strategy of implementing satellite, reanalysis, and surface measurements together provided strong evidence that unhealthy ozone anomalies at the ground were incurred primarily by STE in these events and setup future studies of resulting ozone signatures.

November 2, 2011: Congratulations to our Physics Graduate Students who passed into PhD Candidacy during the past year: Sheng Liu (mentor: Dr. Johnson), Felipe Vallejo Monsalve (mentor: Dr. Hayden), Tao Peng (mentor: Dr. Shih), Malachi Tatum (mentor: Dr. Turner), Anthony Davidson (mentor: Dr. Worchesky), Gergely Dolgos (mentor: Dr. Martins), Steven Buczkowski (mentor: Dr. Martins). These students were honored at the annual Graduate School Doctoral Candidates Reception last night. Pictured (left to right) are Anthony Davidson, Dr. T. Worchesky, and Malachi Tatum.

On 2011 Oct 28 the NPP satellite was launched successfully from Vandenberg AFB. NPP is an acronym for the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project [acronyms can be your friend!]

NPP is the first of a new generation of satellites to monitor/predict the long-term climate change AND short-term weather conditions. One of the several instruments on board is the Cross-track Infrared Sounder (CrIS) that provides spectra in ~1300 bins in 3 important bands in the infrared part of the electromagnetic spectrum. UMBC Physics Professor Dr Larrabee Strow leads a team calibrate CrIS. The instrument can measure Earth's surface temperature and atmospheric parameters such as the major 'Greenhouse Gases' H₂0, CO₂ (carbon dioxide) & CH₄ (methane).

See Also:
http://www.umbc.edu/blogs/umbcnews/2011/10/umbc_researchers_develop_senso_1.html
http://www.umbc.edu/hpcf/research/projects/strow1.html

Abou successfully defended his PhD dissertation on October 11, 2011.

TITLE:
Measurement of the nonlinear refractive index of TeO2 fiber by using IGA technique.

ABSTRACT:
Nonlinear phenomena in optical fibers have been attracting considerable attention because of the rapid growth of the fiber optics communication industry. The increasing demand in internet use and the expansion of telecommunications in the developing world have triggered the need for high capacity and ultra-fast communication devices and also the need to increase the number of transmission channels in the fibers. Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) systems are capable of transmitting large volumes of data at very high rates into huge numbers of optical transmission channels. This ability is limited by the gain bandwidth of Silica based fiber optics amplifiers already installed in the communication networks. Tellurite based fiber amplifiers offer the necessary bandwidth for amplification of WDM and DWDM channels.

This research is for measuring accurately the nonlinear refractive index of Tellurite fibers using the Induced Grating Autocorrelation (IGA) Technique. To investigate these emerging fibers in the telecommunication field, a 10 picoseconds Nd:Vanadate ( Nd:YVO₄) laser operating at 1342nm will be used. The goal of this work is to provide accurate and reliable information on the nonlinear optical properties of Tellurite glass fibers, novel fibers with promising future for developing ultrafast and high transmission capacity communication devices.

Amanda successfully defended her PhD Proposal on October 11, 2011.

TITLE:
A DIAGNOSTIC TEST FOR DETERMINING THE LOCATION OF THE GEV EMISSION IN
POWERFUL BLAZARS

ABSTRACT:
An issue currently debated in the literature is how far from the black hole is the Fermi observed
GeV emission of powerful blazars emitted. Here we present a clear diagnostic tool for testing whether the GeV emission site is located within the sub-pc broad emission line (BLR) region or further out in the few pc scale molecular torus environment. Within the BLR the scattering takes place at the onset of the Klein-Nishina regime, causing the electron cooling time to become almost energy independent and as a result, the variation of high-energy emission is expected to be achromatic. Contrarily, if the blazar is outside the BLR, the expected GeV variability is energy-dependent and with amplitude increasing with energy. We demonstrate this using time-dependent numerical simulations of blazar variability, and propose to apply the diagnostic test using Fermi data. The proposed work holds the promise of settling this important issue.

Anthony successfully defended his PhD proposal on October 6, 2011.

TITLE:
SiGe Quantum Well Thermoelectrics.

ABSTRACT:
This presentation will propose a project examining the effects of semiconductor superlattices on thermoelectric properties in the goal of getting large enhancement for power harvesting from exhaust gas in automobiles.

Sheng successfully defended his PhD dissertation on August 30, 2011.

TITLE:
Investigation of Carrier Dynamics and Nonlinear Effects in Quantum Cascade Lasers using Femtosecond Mid-Infrared Pulses

ABSTRACT:
Quantum cascade lasers (QCLs) are semiconductor lasers based on intersubband transitions and resonant tunneling, emitting mid- to far-infrared light. This dissertation used femtosecond (fs) mid-IR pulses generated by difference frequency generation (DFG) to investigate the ultrafast carrier dynamics and nonlinear effects in QCLs.

In this work, the carrier dynamics of high wall-plug efficiency designed QCLs were investigated utilizing fs mid-IR degenerate pump-probe technique. We observed ultrafast gain recovery within the first 200 fs due to the thin injector barrier inducing fast electron resonant tunneling, fast depletion from lower lasing level by two-phonon resonance design, and relaxation from the continuum region. The observed gain recovery oscillation is interpreted as electrons excited by incoming photons up to higher subbands or continuum region then falling into the next periods of active region so as to dramatically increase the gain on a short time scale. Later, slower gain recovery (2-3 picoseconds) is observed by electron transport through the injector region of the superlattice structure and tunneling into the next period of active region. Another ultraslow recovery component (hundreds of picoseconds) is likely caused by the electron heating and cooling effects as well as the collection of electrons into the lower subbands in real space and compensated by the external bias supply. The latter contribution is support by the observed positive photoconductivity with increased current and decreased voltage across the QCL.

We studied the SHG signal generated by focusing different polarizations (TE and TM modes) fs mid-IR pulses into the QCLs active core. SHG due to intersubband transitions is observed when the pump is TM polarized (SHG_TM). The measured SHG_TM spectrum narrows when the bias across the QCL increases due to the electron population re-distribution and subband realignment. The expected quadratic dependence of the SHG_TM with mid-IR pump power is observed, but saturates at higher pump powers. The observed SHG pumped by TE polarized fs mid-IR pulses (SHG_TE) is most likely generated by the bulk nonlinearity of the InP substrate. The second order nonlinearity for SHG_TE is also confirmed, without observing the saturation. We estimated linear-to-nonlinear power conversion efficiency for both SHG_TM and SHG_TE.

Malachi successfully defended his PhD Proposal on August 26, 2011.

TITLE:
Modeling of Outflows in Active Galactic Nuclei using X-Ray Data

ABSTRACT:
X-ray spectra of Active Galactic Nuclei (AGN) show absorption and emission features that are thought to arise from highly-ionized, fast accretion disk winds. These outflows carry a significant fraction of the accretion energy and connect the supermassive black holes of AGN to their host galaxies. However, the physical mechanism driving them, the conditions in the gas, and the radial location of the outflow have yet to be understood. In the research that will comprise my thesis, I propose using an existing Compton-thick wind model and archived X-ray observational data to study and better understand the wind components of AGN. The sample of AGN used in this study are selected because of their bright X-ray uxes and long exposure times on the current X-ray telescopes (Chandra, XMM-Newton, and Suzaku). Our goal is to test the model to determine if it constrains the wind parameters. This test may offer insight into how dominant the disk wind model is in the X-ray band.

Felipe successfully defended his PhD Proposal on August 25, 2011.

TITLE:
Modeling and design of waveguide structures for generation of terahertz pulses through optical rectification

ABSTRACT:
In this work I propose to develop theoretical models to study the generation of broadband terahertz (THz) pulses through optical rectification (OR) of an input infrared (IR) femtosecond (fs) pulse in waveguide structures composed of a layer of poled electro-optic (EO) polymers embedded within dielectric cladding layers and possibly metal capping layers. The main goal is to be able to predict the generated THz bandwidth for given input pulse characteristics (pulsed duration, pulse shape, transverse mode profile, etc) and waveguide structure composition (geometrical dimensions and the optical properties of the waveguide composites). The models should also allow to optimize the output bandwidth through variation of the waveguide dimensions and its predictions should agree and somehow correlate to the experimental data of already built waveguide structures.

Sam successfully defended his PhD dissertation on July 28, 2011.

TITLE:
Multi-Scale Analysis of Observations of Tropical Cyclones with Applications to High-Resolution Hurricane Modeling

ABSTRACT:
Numerical modeling of tropical cyclones is one of the primary forecasting tools used in predicting tropical cyclone track and intensity. There have been improvements in track forecasting during the past decade, but the skill of intensity forecasts has not improved. It has recently become clear that hurricane forecast models may need to go to higher spatial resolution in order to correctly represent small scale processes that are now thought to play a role in hurricane intensity. The research described in this thesis makes contributions to the problem of intensity forecasting through a combination of high resolution hurricane model development and statistical analysis of observations of hundreds of tropical cyclones. The contributions to model development include the extension of an operational forecast model to 3km resolution, a scale where convection begins to be resolved and convective parameterizations become unnecessary. With higher spatial resolution, it becomes important to find new ways of characterizing the statistical properties of the observed wind and mass fields on a range of scales, in order to evaluate whether the model is producing realistic small scale structure. Statistical methods are developed for analyzing in-situ and satellite observations of tropical cyclones that provide guidance for diagnosing small scale variability in hurricane models over a range of scales. Some statistical characteristics were found to be "universal" in that they were found to be the same for most storms, evidence was found for scale invariance, and statistical signatures of small scale turbulence were identified. In addition, a satellite data analysis reveals a connection between storm intensity and height of convection. This work lays the groundwork for some new directions in future investigations into the small scale dynamical processes that play a role in TC intensity.

Gergely successfully defended his PhD proposal on April 28, 2011.

TITLE:
Polarized Imaging Nephelometer Development and Applications for Field and Aircraft

ABSTRACT:
The goal of this research project is to analyze, build, characterize and demonstrate a new airborne instrument for measuring aerosol phase matrix: the LACO/UMBC polarized imaging nephelometer (PI-Neph). We have built a laboratory prototype of this imaging nephelometer concept and the robust airborne version is under construction, funded by the CALIPSO mission (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) under the DEVOTE project (Development and Evaluation of satellite ValidatiOn Tools by Experimenters).

Project success will provide airborne capability to measure phase matrix elements of aerosol particles with an unprecedented angular range at multiple wavelengths. The PI-Neph measurements during the DEVOTE campaign will be analyzed to provide a pilot study showing comparison to RSP (Research Scanning Polarimeter) and HSRL (High Spectral Resolution Lidar) retrievals and to other in situ measurements, especially integrating nephelometers.

Further characterization and testing will prepare the instrument for future aircraft campaigns serving the validation of CALIPSO and RSP retrievals, potentially other aerosol remote sensing instruments and eventually the future ACE mission (Aerosol/Cloud/Ecosystems). A series of in situ experimental flights and ground experiments will enable the use of resultant data for comparison to the new generation of remote sensors. The in situ measurements of aerosol light scattering will enable retrievals of aerosol size and shape distribution and refractive index, which in turn can be compared to lidar, polarimeter or combined polarimeter-lidar retrievals.

Laboratory and/or field studies of polarized phase function of aerosols versus relative humidity will aid in remote sensing of aerosol fields near clouds to help uncover the principles of the aerosol indirect effect on Earth’s climate. The next couple of years of this PhD work will provide the essential bridge between the development, verification and science applications of the PI-Neph, moving toward a proven satellite sensor calibration / validation capability.

Steven successfully defended his PhD proposal on April 26, 2011.

TITLE:
Measurement of Cloud Droplet Distribution Parameters: a polarized, multi-angle eye toward cloud microphysics

ABSTRACT:
From radiative forcing effects to a cloud's evolution toward the onset of precipitation, the droplet size distribution (DSD) in a cloud has tremendous influence on the cloud's development and its impact on Earth climate systems.

Most common remotely sensed droplet size information is centered on retrieving the effective radius of the droplet distribution and, therefore, is largely focused on the radiative effects of the cloud.

Effective radius is but a small part of the picture where cloud microphysics and the connection between cloud evolution and atmospheric aerosols are the focus. For more microphysically motivated studies, higher moments of the DSD are needed. Techniques exist for retrieving the effective variance through the use of the polarized signal in the light scattered from the droplet field. This extends our view into the DSD parameter space but is limited to somewhat narrow droplet distributions.

The UMBC Laboratory for Aerosols, Clouds and Optics (LACO) has developed, and employed in the field, several generations of polarimetric remote sensing cameras to measure droplet distribution information and is currently developing next generation multi-angle, polarimetric imaging instrumentation for aircraft and satellite remote sensing of clouds and aerosols.

This proposal discusses the use of LACO imaging polarimeters for droplet size spectrum measurement and the development of techniques to extend the droplet size retrieval to wider spectra using multi-angle information in future generation imaging polarimeters.

Tao successfully defended his PhD Proposal on February 14, 2011.

TITLE:
Simulation of Multi-photon Qubit for Quantum Computing

ABSTRACT:
Quantum computer has drawn a lot of attention over decades due to its huge potential and the recent progress is encouraging. One of the critical issues of quantum computing is the requirement of entangled states with a large number of particles. Although the study of entangled states greatly advanced our understanding about the physics of multi-particle superposition, we are still facing difficulties producing entangled states with more than three particles. Comparing with entangled states, it is not that difficult to achieve a superposition among a large number of multi-photon amplitudes for chaotic-thermal light.

A set of experiments have been successfully done to simulate Bell-state with two independent thermal radiations. Moreover, I propose a serial of further works to simulate entangled three-photon, generate N-digit qubits as well as multi-photon interferometry of chaotic-thermal light. This can be used for computation purpose, such as factorize a large number.

Yu successfully defended his PhD dissertation on November 19, 2010.

TITLE:
Multiphoton Coherence of Thermal Light

ABSTRACT:
Multiparticle interference is one of the most surprising consequences of quantum mechanics. In quantum theory, interference happens between different yet indistinguishable probability amplitudes. Probability amplitudes can be nonlocal when they are connected with systems including several particles. The interference between these nonlocal probability amplitudes sometimes can only be understood by quantum theory. In this dissertation, the multiphoton coherence of thermal light is studied, theoretically and experimentally, as the consequence of interference between nonlocal probability amplitudes. The study showed that the higher order correlation functions of thermal light had higher contrast compared with the lower order correlation functions. For example, the contrast of the Nth order correlation function of thermal light can reach N!:1. This is because in higher order correlation functions there are more cross terms from interference that contribute to the correlation peak. In this dissertation, the high contrast property is employed to increase the contrast of thermal light ghost imaging. An experiment showed that the contrast of the third order ghost image is significantly improved compared with that of the second order ghost image.

Hao successfully defensed his dissertation on November 19, 2010.

TITLE:
Theoretical Study of Quantum Computation with Nonlinear Optics

ABSTRACT:
Quantum computing has been of intense interest over the last 10 years because of its
promising ability to do high-speed factoring and its potential for the efficient simulation
of quantum dynamics. It could be implemented in many different ways using optical
techniques. A better understanding of the advantages and disadvantages of these
approaches would allow the experimental groups working in this area to optimize their
choice of experiment and to concentrate on the approaches that are most likely to succeed.
In this thesis, we are interested in quantum logic gates based on nonlinear optical
approaches and mainly focus on one of the approaches----quantum Zeno gates. We
theoretically analyze two-photon absorption, which is essential to perform quantum Zeno
gates for coherent light and for frequency-entangled light. We also analyze and compare
quantum Zeno gates with nonlinear phase gates, which is another promising optical
implementation for quantum logic. The results of our theoretical analysis will be useful
for future experimental work in quantum computation.

Anthony successfully defended his masters thesis on August 2, 2010.

TITLE:
Ge PIN on Si

ABSTRACT:
High speed optical interconnects that can be integrated with silicon is being extensively studied to achieve high speed, low noise chip to chip communication. Since silicon does not absorb the standard wavelength in telecommunication (1.55 micron) other materials are required that do not have matching lattice constants to silicon for the photo detectors in the interconnects. Two types of thin buffer layers have been introduced to prevent dislocation propagation into the device layers to achieve maximum performance. Fabrication of the photo detectors must also follow standard procedures in the semiconductor industry to make the devices mass producible.

The devices studied in this research employed surfactant mediated growth of germanium on silicon with antimony as the surfactant. A brief discussion of the growth method of Molecular Beam Epitaxy and device parameters will be discussed with a large focus on the fabrication process used to create the devices.

Sheng successfully defended his PhD proposal on June 23, 2010.

TITLE:
Measurements of Carrier Dynamics in Quantum Cascade Lasers and Quantum Wells using Femtosecond Mid-IR Pulses

ABSTRACT:
Quantum cascade lasers (QCLs) are semiconductor lasers based on intersubband transitions and resonant tunneling, emitting mid- to far-infrared light. This research will use femtosecond Mid-IR pulses generated by difference frequency generation (DFG) to investigate the carrier dynamics in QCLs and quantum well (QW) structures grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) in Princeton University, UMBC and CCNY.

Due to the ultrafast carrier dynamics such as tunneling, electron-electron scattering, and electron-phonon scattering, which occurs on the timescale of femtoseconds to picoseconds, femtosecond pulses are necessary to time resolve these phenomenon. We utilize Mid-IR resonant pumping of the intersubband transitions to eliminate interband electron-hole generation and heavy and light-hole effects, in this unipolar device.The spectra and pulse duration of the fs Mid-IR pulses are measured using a Fourier transform infrared (FTIR) spectrometer and two-photon absorption autocorrelation, respectively.

In the pump-probe technique a strong pump beam is coupled into the QCL to change the population difference between upper and lower lasing level so as to perturb the steady-state gain from equilibrium. A second weaker time-delayed probe beam is used to monitor the evolution of the electron population – this pump-probe signal is directly related to the occupation probability of the carriers in each energy level. Additionally, effects such as coherent tunneling, Bloch oscillations, Rabi oscillations, homogeneous and inhomogeneous scattering, and dephasing effects in two dimensional nanostructures may also be studied with this measurement technique. The carrier dynamics in different designed QCLs at room temperature and low temperature will be investigated. Using transition rate equations for the QCLs, photon-driven transport, phonon-assisted relaxation, resonant tunneling, and superlattice transport and relaxation will be ascertained. These results will provide us a better understanding of the physics of QCLs and QW structures, which would further help us to improve the design and performance of QCLs.

Paul successfully defended his PhD proposal on Monday, May 17, 2010.

TITLE:
Applying Nuclear Decay Models to Schizophrenia

ABSTRACT:
Schizophrenia is a crippling mental illness that disables schizophrenics for life. This disability is a burden shared by those affected and society. Research has not identified a definitive cause of schizophrenia, rather a patchwork of hypotheses have been advanced. A novel model that is isomorphic to the model governing radioactive decays sheds new light on schizophrenia.

A rich variety of epidemiological data is available to model. The model’s parameters have specific physical meaning, which serve as a guiding principle in searching for the causes of schizophrenia. This model will challenge the conventional wisdom about schizophrenia and explain various features of schizophrenia epidemiology. Preliminary results show a majority of the population is immune to schizophrenia. The model points towards the physical processes associated with the etiology of schizophrenia.

Meimei successfully defended her PhD proposal on Monday, May 17, 2010.

TITLE:
Quantum Information Processing with Tapered Optical Fibers

ABSTRACT:
The race between various approaches (ions, NMR, photons, etc.) to quantum computing has been becoming more and more fierce since the idea of quantum computer came up in the early 1980’s. The research on the quantum information processing is not only providing us with the possibility of a revolutionary computer which can do several important things (quantum simulation, large number factorization and database searching) that are difficult or impossible on a traditional computer, but also giving us profound understanding and new insights about nature.

Our group has been interested in an optical approach to quantum computation and proposed a universal optical quantum logic gate that uses the quantum Zeno effect to prevent errors associated with two photons exiting a device in one mode. These “Zeno Gates” require very strong Two-Photon Absorption (TPA) but very weak single photon absorption (SPA). In addition to Zeno Gates, strong TPA can be also used to realize ultra efficient classical optical switches, and it is a promising tool to develop a new kind of single photon source.

My PhD research will primarily focus on the experimental realization of strong TPA with weak light beams. The system we will be using consists of a sub-wavelength diameter Tapered Optical Fiber (TOF) suspended in Rubidium vapor. Once achieved, this strong TPA system will also allow us to investigate a number of other effects in quantum optics and quantum information processing. Recent experimental progresses on the development of a state of the art TOF fabrication system and future plans will be discussed.

2010 is the 50th anniversary of the construction of the first successful laser. Dr. Anthony M. Johnson, Director of CASPR, Professor of Physics and Professor of Computer Science & Electrical Engineering at UMBC has been named as a "Laser Pioneer" by Laserfest, the official website for the yearlong celebration.

In an associated interview, Dr. Johnson describes some of his motivation to promote underrepresented minorities to pursue careers in science, and recent work to use of lasers for environmental and health purposes.

The following Physics students will be inducted into Sigma Pi Sigma, the National Physics Honor Society at the annual Physics Picnic: Benjamin Ecker, James Gerity, Cameron Howard and David Mason.

The UMBC chapter of Sigma Pi Sigma was established in 1980. It exists to honor outstanding scholarship in Physics; to encourage interest in Physics; to promote an attitude of service of its members towards their fellow students, colleagues and the public; and to provide a fellowship of persons who have excelled in Physics. Undergraduate candidates shall have attained at least a 3.25 grade point average on 4.0 system for Physics courses and at least a 3.0 grade point average for cumulative course grades in all courses. The inductees will also be recognized at the 5th Annual CNMS Student Recognition Day on May 7, 2010.

Vincenzo successfully defended his dissertation on April 26, 2010.

TITLE:
Theoretical and experimental study of a new algorithm for factoring numbers

ABSTRACT:
The security of codes, for example in credit card and government information, relies on the fact that the factorization of a large integer number N is a rather costly process on a classical digital computer. Such a security is endangered by the Shor's algorithm which employs entangled quantum systems to find, with a polynomial number of resources, the period of a function which is connected with the factors of N. We can surely expect a possible future realization of such a method for large numbers, but so far the period of Shor's function has been only computed for the number 15.

Inspired by Shor's idea, our work aims to methods of factorization based on the periodicity measurement of a given continuous periodic "factoring function" which is physically implementable using an analog computer.

In particular, we have focused on both the theoretical and the experimental analysis of Gauss sums with continuous arguments leading to a new factorization algorithm. The procedure allows, for the first time, to factor several numbers by measuring the periodicity of Gauss sums performing first-order "factoring" interference processes.

We experimentally implemented this idea by exploiting polychromatic optical interference in the visible range with a multi-path interferometer, and achieved the factorization of seven digit numbers.

The immediate development of this work consists of implementing the same factorization physical principle on entangled systems in order to achieve prime number decompositions of large integers with a polynomial number of resources.

Paul successfully defended his dissertation on April 16, 2010.

TITLE:
Optical Pump Terahertz Probe Studies of Semiconducting Polymers

ABSTRACT:
Optical-pump terahertz-probe spectroscopy (OPTP) has been applied to study charge generation, transport and the evolution of the photo-induced excited states in thin film organic semiconductors, with emphasis on their relevance to photovoltaic technology. In these experiments the response of the photoexcited material to the AC electric field of a terahertz (THz) pulse was measured. From this response, the evolution of the complex conductivity in the far-infrared was monitored. OPTP presents advantages over other techniques by being an all-optical probe of the complex conductivity over nanometer scale distances with sub-picosecond resolution and exhibits particular sensitivity to carrier scattering rates, which typically lay in the THz range. Conductivity models were applied to the extracted conductivity curves in order to determine technologically relevant quantities like the charge carrier mobility and external quantum yield of charge carrier generation.

We observed charge carriers generated on a subpicosecond time scale in thin films of polyhexylthiophene (P3HT). Through application of the Drude-Smith model (DSM) over the 0-2 THz band, we determined a room temperature intrinsic mobility of about 30 cm²/Vs. The temperature dependence of the conductivity dynamics showed signs of thermally activated polaron hopping influenced by torsional disorder. Above and below gap excitation resulted in similar dynamics, both showing that the majority of carriers recombine within 1 ps. We were able to observe charge transfer occurring on a sub-ps timescale to the soluble fullerene, PCBM, for both excited states, demonstrating that narrow gap polymers can be blended with PCBM for photovoltaic applications.

We observed charge carrier generated on a sub-ps time scale in thin amorphous films of metalated polymers. The time evolution of the conductivity showed that charge carriers recombine and only excitons persist after 100 ps. This characteristic appears to be common to amorphous systems. An intrinsic mobility of 20 cm²/Vs was found for the most promising material.

Broadband (0-6 THz ) studies of the photoconductivity in P3HT suggest that the hole mobility is lower than initially determined. They also bring into question whether the DSM can describe the conductivity effectively or whether delocalized polaron transitions at higher frequencies are the origin of the observed features.

Li successfully defended her PhD proposal on Monday, April 12, 2010.

TITLE:
Aerosol Absorption Measurements Using Satellite Remote Sensing

ABSTRACT:
Aerosols, the solid or liquid particles suspended in the atmosphere, directly affect the
energy balance of the Earth’s climate system by scattering and absorbing solar radiation.
Aerosol absorption can warm the atmosphere and cool the Earth’s surface, hence aerosols
can affect the atmospheric temperature profile, boundary layer evolution, convection,
cloud formation, and precipitation, particularly over the regions where significant amount
of aerosol absorption occurs.

Much research has focused on studying aerosol absorption properties. One method of
studying aerosol absorption properties is called the critical reflectance technique. The
critical reflectance technique has the unique advantage of providing continuous
measurements and global coverage when it is applied to satellite data. Specifically, it uses
satellite data from two days (a clean day and a polluted day with the same observing
geometry) to retrieve aerosol single scattering albedo (SSA) - the ratio of the aerosol
scattering coefficient to the sum of the aerosol scattering and absorption coefficient.

Using the critical reflectance technique we have investigated how sensitive the retrieved
SSA is to the following factors: aerosol optical depth (AOD), the real part of the
refractive index, detector zenith angle, AOD difference between the polluted day and the
clean day, and changing aerosol types between both days. In addition, we applied this
technique to Moderate Resolution Imaging Spectroradiometer (MODIS) data over South
Africa and South America. The validation results show that SSA from MODIS retrieval
is in good agreement with AERONET SSA within one standard deviation.

I propose to continue studying aerosol absorption properties retrieved from MODIS data
using the critical reflectance technique and its application to climate forcing. I will
quantify the uncertainty of critical reflectance and SSA and extend the SSA retrieval to
all MODIS wavelengths with enough signal and other AERONET stations. I will also
validate retrieval results with AERONET and other available measurements.
Furthermore, to better understand how aerosol absorption affects the Earth’s energy
balance, I will determine the aerosol radiative forcing at the Earth’s surface and the top of
the atmosphere. In addition, I will produce regional SSA maps and provide aerosol
absorption information to aid in aerosol semi-direct effect studies.

Colin successfully defended his dissertation on April 8, 2010.

TITLE:
Electro-optic polymers for terahertz applications

ABSTRACT:
The rapid development of technologies employing terahertz (THz) radiation has led to numerous industrial and scientific applications. Current THz technologies are limited in their frequency response because of phonon absorbance and poor phase matching in crystalline emitters and detectors, or are limited to high-power bench-top pump laser systems for air-plasma generation and detection. In contrast, amorphous electro-optic (EO) polymer composite materials have the potential for broad bandwidth, spectral gap-free THz emission and detection while requiring a relatively low pump laser power.

In this thesis a theoretical description of THz radiation emission and detection using EO polymers is reviewed, including the effects of laser spectral bandwidth, pulse distortion, and material properties of the EO media. This model is used as a guide to improve the response of a THz system employing electro-optic polymer emitters and detectors. EO polymer composites that have been engineered for terahertz applications are described. These materials show a progression of improvements for use in THz systems, including higher EO coefficients, increased photostability, and reduced aggregation and dimerization.

A study of in-plane (longitudinal) and parallel-plate (transverse) poling of EO polymers for use as THz sensors is presented, including a theoretical description of detection sensitivity for each device. In-plane poling allows access to the full optical nonlinearity of the EO polymer, potentially increasing detection sensitivity by a factor of 2.4 over parallel-plate poled devices. A transmission ellipsometric EO measurement technique is developed for the in-plane poling device and is used in the experimental comparison of the two devices.

EO polymer composites are employed as terahertz emitters and sensors in systems using a communication-wavelength pump laser. A 15 THz wideband response is achieved using the ALTB203/APC composite, and is compared to the organic crystal DAST and to the THz system model. Increasing emitter thickness is studied through stacking multiple EO polymer emitter films. Frequency-dependent terahertz index and absorption of the emitter and sensor films are included into the THz model for a more accurate representation of the terahertz system response.

Given proper phase-matching and low absorption, EO polymer materials can potentially be used in a waveguide geometry to generate broadband THz radiation. Coupling these devices with currently-available ultra-fast fiber lasers could lead to the development of field-deployable, compact, inexpensive THz systems.

Raymond successfully defended his dissertation on February 5, 2010.

TITLE:
Nonlinear Optical Properties of Novel Forms of Enriched Carbon Disulfide

ABSTRACT:
The ultimate goal of designing molecules with large third-order nonlinearities is to incorporate them into optical switching and limiting devices. To achieve this, the molecules must have large and fast optical nonlinearities. We undertook picosecond and femtosecond studies of carbon disulfide (CS₂) enriched with sulfur, selenium, cadmium telluride nanoparticles and 2-methyl-4-nitroaniline (MNA) for enhanced optical nonlinearities, using the Z-scan technique. In this method, a sample is scanned along the optic axis (chosen as the z- direction) in the focal region of a single focused laser beam. The intensity transmitted through an aperture (nonlinear refraction) or without an aperture (nonlinear absorption) in the far field is recorded as a function of the sample position. Due to the high intensity of the electromagnetic field in this region, the sample tends to behave as a lens of variable focal length and can focus or defocus the beam depending on the sign of the nonlinearity. Our measurements with a 130-fs source indicate that the nonlinear absorption coefficient of CS₂ was enhanced by more than two orders of magnitude (over pure CS₂) through sulfur and selenium enrichment; while their nonlinear refractive indices experienced minimal change. Enhanced nonlinearities of enriched CS₂ molecules may be harnessed for sensor applications.

Rob successfully defended his dissertation on December 7, 2009.

TITLE:
Theoretical and Experimental Study of the Nonlinear Optical and Dispersive Properties of Conventional and Photonic Crystal Fibers

ABSTRACT:
The early use of the induced grating autocorrelation (IGA) method to measure the nonlinear refractive index of single mode fibers utilized 50-70 ps pulses at 1064-nm and required only 15-20 m lengths of fiber. Exotic fibers, such as photonic crystal fibers (PCFs), are extremely expensive and limit many applications to a few meters. Therefore, a practical measurement of the nonlinear coefficient for such exotic fibers requires a technique sensitive to shorter fiber lengths (< 5 m). To reduce the fiber length requirements, the IGA technique must use shorter pulses.

In this work, a new mathematical description was developed for the IGA technique that is applicable to pulses as short as 100 fs. This model includes effects such as dispersion, self-phase modulation, stimulated Raman scattering, intra-pulse Raman scattering and self-steepening. The model was used to investigate pulse propagation at three pulsewidths: 50 ps, 2 ps, and 120 fs. The model predicted the sensitivity of IGA measurements to dispersive and nonlinear effects at these pulsewidths.

The numerical model led to the successful experimental determination of both the dispersion and nonlinear coefficients of a 15m long single-mode fiber using a 2 ps Ti: sapphire laser at 800 nm. The nonlinear coefficient for several PCFs (a 35 cm long highly nonlinear PCF and two large mode area PCFs of 4.5 m and 4.9 m long) were also successfully measured with excellent numerical fits using this new IGA model.

Nathan successfully defended his dissertation on November 23, 2009

TITLE:
Application of satellite laser altimetry data to studies of sea ice properties and processes

ABSTRACT:
Sea ice plays an important role in the global climate system by impacting the energy balance of the Earth as well as affecting the oceanic and atmospheric circulations. Recently, large changes have been observed in the Earth's areal coverage of sea ice. However, little is currently known about sea ice thickness particularly at the scales needed for climate research. Spaceborne remote sensing provides the necessary global scale of coverage, but the retrieval of sea ice thickness from space has not been possible until recently with the launch of satellite altimeters of high accuracy and precision. The Ice, Cloud, and land Elevation Satellite (ICESat) is one such laser altimeter with the potential to retrieve sea ice freeboard, which, when combined with snow depth retrievals and the assumption of hydrostatic balance allows for the determination of sea ice thickness. The goal of this study is to use data from ICESat to provide sea ice thickness values at the global scale and high spatial resolution needed for climate studies. The work presented in this thesis includes the validation and improvement of ICESat data products, development and validation of sea ice freeboard retrieval algorithms using the ICESat data products, and the development of a method to combine ICESat freeboard retrievals with a snow depth data set to determine sea ice thickness at the 70 m spatial resolution of ICESat. The ICESat data set is used to study sea ice thickness, heat exchange, and ice production in the Arctic Ocean for the 2003-2008 time period. Despite the thinning of the Arctic sea ice cover over the 2003-2008 time period, mean ice growth rates for consecutive fall and winter measurement periods remained relatively constant. An increased ice growth rate which may be expected from a thinner ice cover appeared to be balanced by warmer temperatures. An increased ocean-atmosphere heat flux is also observed due to the thinning of the sea ice cover.

Nestor successfully defended his masters thesis on November 13, 2009

TITLE:
Broad band terahertz time domain spectroscopy on polymers and organic electro-optic polymers

ABSTRACT:
Several polymers and two organic polymer composites were studied using terahertz time domain spectroscopy and analyzed using Duvillaret’s method and a dynamic range analysis to determine their credible bandwidth. Terahertz time domain spectroscopy is a technique that allows us to determine the real index of refraction and the absorption of nonconductive materials in the terahertz band. These polymers are used as hosts to build organic composites for terahertz generation through optical rectification and detection via electro-optic (EO) sampling. Knowledge of their optical parameters is important when considering them as hosts for emitters and detectors. Also, the knowledge of these parameters over a wide bandwidth is important in the determination of the degree of phase matching that these materials can have, for a given center wavelength of an optical pump pulse. Broad bandwidth and a clear spectrum were achieved with an air-plasma emitter and an organic EO polymer sensor. In this thesis a bandwidth that goes from 0.7 to 9 THz for the real index of refraction and for the absorption coefficient for the majority of the polymers, is reported.

Hui successfully defended his PhD proposal on September 3, 2009

TITLE:
The high-order quantum coherence of thermal light

ABSTRACT:
Fifty years ago, Hanbury Brown and Twiss (HBT) discovered a nontrivial intensity‐intensity correlation that the thermal light has a twice chance of being measured by two individual photo‐detectors within its coherence volume. This HBT effect was finally interpreted as intensity fluctuation. However, with careful theoretical and experimental studies, we found that intensity fluctuation faces difficulty. Recently, our theoretical and experimental works have provided some clear evidences. Moreover, we propose a serial of further works, in order to explicitly demonstrate that the HBT effect has to be described quantum mechanically as two‐photon interference.

John successfully defended his masters thesis on August 25, 2009

TITLE:
Atomic Layer Deposition of TiO₂ on Si and GaAs Substrates Using TDMATi and H₂O Precursors

ABSTRACT:
Atomic Layer Deposition (ALD) has emerged as an effective method for depositing high-quality, conformal thin films with thickness control on the monolayer level. With a homemade hot-wall, flowtube ALD reactor, TiO₂ films were deposited on Si and GaAs substrates using TDMATi and H₂O precursors. Spectroscopic ellipsometry (SE) measurements show an optimal growth rate at a furnace temperature of 200°C. SE was also used to measure the index of refraction of the films. XPS analysis indicates that the films have very little bulk contamination and are slightly over-oxidized. FTIR and XRD were used to examine film crystallization. RBS measurements of the coverage of Ti atoms were conducted over a comprehensive range of film thicknesses. AFM produced topographical images of the film surfaces that indicate RMS values of 3-4% of the film thickness.

Interfacial oxide layers are an undesired consequence of many metal-oxide/semiconductor stacks. Analysis of the films deposited on GaAs substrates focused on the interfacial native oxide layer. Films that were grown on top of a 25Å native oxide layer consumed the oxide during deposition almost completely. This “self-cleaning” effect has been attributed to methylamino ligands of the TDMATi precursor molecules.

Ross successfully defended his masters thesis on July 29, 2009.

TITLE:
Forcing Mechanisms For Heavy Precipitation in the Extratropical Transition of Atlantic Hurricanes

ABSTRACT:
Freshwater flooding is the number one inland killer associated with hurricanes that make landfall in the Mid-Atlantic region. Although great improvements in hurricane track forecasting have been made over the past decade, forecasting hurricane intensity change and rainfall has remained problematic. This challenge becomes even more difficult after the storm makes landfall. Over land, storms typically weaken; however, strong nonlinear interactions with mid-latitude systems or forcing from terrain can reintensify the storm or trigger extreme precipitation events. The goal of the work presented here is to better understand the physical processes that lead to heavy precipitation and storm reintensification during the extratropical transition of hurricanes in the Mid-Atlantic region. We use the North American Regional Reanalysis to analyze in detail two landfalling storms: Hurricane Gaston (2004) and Hurricane Ernesto (2006). Both storms presented forecast challenges and both resulted in heavy precipitation, although through different mechanisms. Gaston was shown to create its own baroclinic zone, which led to heavy rainfall and latent heat release which allowed the storm to briefly rejuvenate over land. Ernesto interacted strongly with an upper level trough and jet, which created a secondary circulation that fueled the storm with moisture from the Atlantic. A potential vorticity analysis shows evidence for a case of stolen identity and possible stratosphere-troposphere exchange (STE). Diabatic forcing in the mesoscale proved to be most important in the transition of Gaston, whereas synoptic scale interactions were crucial to the evolution of Ernesto, which also occluded very quickly. The various spatial scales and rapid transitions of both these storms provide insight into the forecasting challenges during these transition events.

Shelly successfully defended her masters thesis on July 20, 2009.

TITLE:
A study of Surface Plasmon-Coupled Emission from Rhodamine 6G using picosecond pulses

ABSTRACT:
Fluorescence measurements are used in life sciences to provide important information
about biomolecules (fluorophores) such as structure, mobility, and conformational
changes by detecting the target molecules on surfaces. Currently, fluorescence
measurements are performed using free-space (FS) detection, which are mostly isotropic,
resulting in detection of approximately 1% of the total emission. The emission process
may be limited by the background fluorescence due to its isotropic nature and,
photochemical destruction of the fluorophores.

Surface Plasmon-Coupled Emission (SPCE) is a fluorescence technique that has been
recently introduced that increases the fluorescence yield. SPCE is based on the
interaction of excited-state fluorophores with a nearby metal surface. The fluorophores
above the metal surface can couple with the plasmon resonances in the metal, resulting in
directional and wavelength-resolved emission. The coupled emission is characterized by
a dependence of the emission wavelength on the emission angle. In addition, the
emission is horizontally (p) polarized. An advantage of the SPCE over FS signal is the
reduction of the background fluorescence signal, since only fluorophores close to the
metal surface will couple to the surface plasmons.

Picosecond pulses were used to study the SPCE properties of Rhodamine 6G fluorophore
on a thin silver film. It is expected that using pulsed laser sources can greatly enhance
the SPCE signal over the FS signal. The SPCE signal is 3 times higher that the isotropic
FS signal. Thus, SPCE technique under pulsed excitation promises to be an effective tool
for fluorescence measurements in investigating the optical properties of biomolecules.

Chris successfully defended his thesis proposal on June 12, 2009.

TITLE:
A Remote Sensing Study of Boundary Layer Venting during Dynamic Events with the Atmospheric Emitted Radiance Interferometer (AERI)

ABSTRACT:
The study of atmospheric processes in the planetary boundary layer (PBL) is a very complex and interesting field. By definition, the PBL is the region of the atmosphere with turbulent motions resulting from the no-slip boundary condition with the surface, and its depth can range from 30 meters in conditions of large static stability to up to 3 kilometers in highly convective regimes. This project will quantify mixing of trace gases including CO, O₃, and H₂O into and out of the boundary layer. Our focus will be on days when either Horizontal Convective Rolls (HCR) or Low Level Jets (LLJ) occur in the boundary layer. New remote sensing techniques to retrieve information about the trace gases will be further developed using the Atmospheric Emitted Radiance Interferometer (AERI). Specifically, we will update the current CO retrieval algorithm which retrieves one mixing ratio value for the entire troposphere. The improvements will be to obtain values for CO in the boundary layer and in the free troposphere. CO’s 1-2 month lifetime makes it an excellent passive tracer of atmospheric motions; thus, monitoring it will quantify mixing from the boundary layer to the free troposphere. To validate the CO retrieval, we will utilize the 3+ years (2006-2009) of aircraft CO profiles obtained at the United States Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site near Lamont Oklahoma. A comparison of work already done on the new retrieval compared to the old retrieval will be shown. Also, a presentation of case study days of LLJ and HCR will highlight the need to improve the retrieval.

Andy successfully defended his masters thesis on June 11, 2009

TITLE:
Neural Networks and Atmospheric Scattering Calculations

ABSTRACT:
For the majority of the particles in the atmosphere, calculations of scattering energy loss are increasingly accurate in proportion to the computing time afforded them. Accurate radiative transfer calculations, even with the most efficient numerical methods, are computationally expensive. This becomes a serious problem for multi-decadal climate simulations for which an accurate representation of the radiative impact of atmospheric constituents is crucial. This thesis presents one method for reducing the computational expense radiative transfer calculations of aerosol scattering properties, which are used in chemical models. The goal of this research is to develop a fast scattering code using a neural network that is trained on input and output data derived from an accurate T-Matrix scattering algorithm. The input space to the neural net consists of scattering parameters that describe the atmospheric scattering conditions such as wavelength of incoming light, effective particle radius, and index of refraction. The output space consists of the coefficients of a Legendre polynomial expansion of the phase function. The neural net finds the nonlinear mapping between the input and output spaces for a training set and can subsequently be used to generate the phase function for arbitrary wavelength, particle radius and index of refraction. In this research, a neural network applicable to both Lorenz and Mie scattering is developed and tested for both accuracy and speed. The accuracy of the neural net is found to be excellent, with errors well below 10%, and runtime testing shows that the neural net is approximately 5 times faster than a lookup table.

Congratulations to (L to R) Drs. Jianning Zeng, Antonia Gambacorta, Timothy Bole and (not pictured) Mengsteab Weldegaber who graduated on May 20th, 2009. Their thesis topics ranged from the effects of electromigration on structures at the nanoscale, to feedback processes and boundary-layer phenomena in the atmosphere, to the study of emission on the scale of thousands of light-years in nearby galaxies.

Congratulations also to Eric Hughes, who was awarded an M.S. at the ceremony.

The following students have earned the following departmental awards:
    Joseph Dulny III - Outstanding Graduating Senior in Physics
    Sheng Liu - Joseph F. Mulligan Memorial Lectureship
    Aaron B. Pearlman - Donald N. Langenberg Undergraduate Research Award.
The awardees were recognized at the 4th Annual CNMS Student Recognition Day on May 8, 2009.

The following Physics students have been inducted into Sigma Pi Sigma, the National Physics Honor Society: John Carrico, Joseph Dulney III,Derek Fertig, Rory Holderness, Joseph Jancasz, and Shauna Marquess.

The UMBC chapter of Sigma Pi Sigma was established in 1980. It exists to honor outstanding scholarship in Physics; to encourage interest in Physics; to promote an attitude of service of its members towards their fellow students, colleagues and the public; and to provide a fellowship of persons who have excelled in Physics. Undergraduate candidates shall have attained at least a 3.25 grade point average on 4.0 system for Physics courses and at least a 3.0 grade point average for cumulative course grades in all courses. The inductees were recognized at the 4th Annual CNMS Student Recognition Day on May 8, 2009.

Eric successfully defended his masters thesis on May 1, 2009.

TITLE:
Using Horizontal Transport Characteristics to Infer an Emission Height Timeseries of Volcanic SO2

ABSTRACT:
Characterizing the emission height of sulfur dioxide (SO2) from volcanic eruptions yields information about the strength of volcanic activity, and is crucial for the assessment of possible climate impacts and for validation of satellite retrievals of SO2. Sensors such as the Ozone Monitoring Instrument (OMI) on the polar-orbiting Aura satellite provides accurate maps of the spatial distribution of volcanic SO2, but provide limited information on its vertical distribution. The goal of the work presented here is to explore the possibility of using a trajectory model to reconstruct both the temporal activity and injection altitude of a volcanic source from OMI column measurements of SO2 observed far from the volcano. Statistical analyses based on the distance of closest approach to the volcano of back trajectories initialized at the measurements are compared to an optimal reconstruction based on forward trajectories. The inferred altitude of the SO2 cloud is compared to the altitude of derived sulfate aerosols detected in aerosol backscatter vertical profiles form the CALIOP instrument aboard CALIPSO. The trajectory modeling analyses also provides details about the horizontal transport that are not clearly apparent from satellite measurements alone; revealing an interesting transport mechanism occurring in the subtropical jet stream.

Mengs successfully defended his dissertation on April 28, 2009.

TITLE:
Investigation of Stable and Unstable Boundary Layer Phenomena Using Observations and a Numerical Weather Prediction Model

ABSTRACT:
Despite significant advances in the simulation of synoptic scale weather events, current numerical weather prediction models show poor skill in their capability to accurately simulate sub-grid scale features, such as cloud-precipitation processes and planetary boundary layer (PBL) evolution, because too many semi-empirical parameterizations are involved. The goal of the work presented here is to evaluate the next-generation mesoscale Weather Research and Forecasting (WRF) model in simulating mesoscale weather phenomena under different PBL stratifications. The work presented in this thesis investigates the performance of the state-of-the-art mesoscale WRF model in simulating the structure and development of a daytime convective boundary layer phenomenon, (the dryline over the Southern Great Plains), and a nocturnal stable boundary layer phenomenon, (the Low-Level-Jet (LLJ) over the Mid-Atlantic region). The dryline and LLJ are two examples of boundary layer phenomena that occur under very different conditions and thus together they provide a good test of the PBL dynamics in the model. Extensive, high spatial and temporal resolution data collected during these case studies is used to evaluate the numerical results. For the unstable boundary layer, a detailed observational analysis of a non-convective dryline investigates an incorrect forecast. For the stable boundary layer, the accuracy of the timing and spatial characteristics of the LLJ for different PBL parameterizations is investigated and discussed in terms of the LLJ forcing mechanisms.

Jianning successfully defended her dissertation on April 22, 2009.

TITLE:
Extended Emission Surrounding Nearby Seyfert Galaxies

ABSTRACT:
We present the results from a search for and survey of any extended X- ray emission surrounding a class of Active Galactic Nuclei (AGN) known as “Seyfert-2” galaxies using data collected using Chandra X-ray observatory (CXO). The mirrors of this work was therefore to determine whether CXO observations help constrain current theories for AGN by probing the smallest spatial scales (> 100 pc) possible. Our sample consists of all the CXO observations of Seyfert-2 galaxies performed using the ACIS-S3 detector during the first 8 years of operation (28 objects). We find extended X-ray emission in all our Seyfert-2 sample of galaxies with a range of luminosities (10³⁸ ∼ 10⁴¹ erg s⁻¹ ). For 18 objects, the morphology is predominately bi-conical centered on the nucleus and typically extending out to a few kpc. Only a single cone is seen in 8 of the remaining ob jects, which may be indicative of intrinsically anisotropic emission. Where data is available, the X-ray cones do appear to occupy the same solid angle as the extended [OIII] emission line gas previously detected in these objects.

Our data suggest that the luminosity of the extended emission is typically a few percent of that of the nuclear source. Our findings are therefore broadly consist with current theories of AGN, but the low signal to noise for many of the observations combined with obscuration and possible contamination prevent any definitive tests of “Unified Schemes” being performed. Unfortunately this is likely to be the case for the foreseeable future.

Tim successfully defended his dissertation on February 5, 2009.

TITLE:
A Study of the Effects of Electromigration on Structures at the Nanoscale

ABSTRACT:
This thesis summarizes a study of the effects of electromigration, or diffusion influenced by applied electric fields, on nanoscale metallic structures. We have studied the impact of electromigration on two types of nanoscale systems, and as such the thesis naturally divides into two portions.

In the first portion, consisting of Chapters 2-4, we investigate the effects of electromigration on fluctuating step edges. When there is no electromigration present, a step undergoing motion by diffusion of atoms along its edge demonstrates power-law scaling in temporal correlation functions. This is verified by approximating the step as a continuum and using Langevin analysis; this approach is then extended to include electromigration forces. Under electromigration conditions, specifically for electromigration forces directed into or away from the step, we find theoretical deviations from the power-law scaling in the correlation function. We demonstrate this in two ways: through Monte Carlo simulation of step edges under electromigration conditions and through analysis of experimental measurements of current-stressed steps at the surface of silver films. We found good qualitative agreement with the theoretical expectations in both simulation and experiment, as well as good quantitative agreement in the results of the simulations.

The second portion of the thesis, consisting of Chapters 5 and 6, details an investigation of the effects of electromigration on the Rayleigh-Plateau instability in solid nanowires. We begin by deriving an equation of motion for a continuous cylinder and including an electromigration force along the symmetry axis of the cylinder. This is equivalent to a model of a nanowire carrying current, where the electromigration force is modeled as a constant.

We find power-law scaling in the pinching process with and without electromigration, though the effects of electromigration are to extend the life of the nanowire relative to those without electromigration. This is confirmed by conducting kinetic Monte Carlo simulations of aluminum nanowires under electromigration conditions. We find good agreement with the continuum model for the exponent in the power-law scaling as well as the effect of electromigration on the time at which pinching occurs. We also find evidence of self-similar behavior in the continuum model as well as in the simulations.

Junlin successfully defended her thesis proposal on January 28, 2009.

TITLE:
Entangled Photon Holes

ABSTRACT:
The concept of quantum entanglement has been identified as a key practical resource for quantum information processing. Over the past 30 years, experiments on entanglement have mostly involved studying correlations of the physical properties (such as polarization or momentum) of two distant photons. Recently, a new form of entanglement called “entangled photon holes” has been discovered. Roughly speaking, the entanglement is due to the absence of the photon pair rather than some physical property of the pairs. Although a recent experiment has provided some initial evidence of the existence of photon-hole states, the entangled nature of the state has not yet been experimentally observed. Here we propose an experimental test of Bell’s inequalities using photon-hole states. If successful, the results of this experiment would explicitly demonstrate the entangled properties of photon-hole states, which would represent a major advance in quantum optics and quantum information science.

Dr. L. Larrabee Strow, Research Professor, is a member of the science team for the satellite IBUKI launched from Japan on January 23rd. IBUKI (also known as the Greenhouse Gases Observing Satellite, GOSAT) is a Japanese mission designed to map the abundance of greenhouse gases in the atmosphere. During its five-year mission it will identify and monitor sources of CO₂ in support compliance with international treaties and agreements such as Kyoto. So far, the number of ground-based CO₂ observation points has been limited, and they have been distributed unequally throughout the world. IBUKI will enable the precise monitoring of the density of carbon dioxide by combining global observation data sent from space with data obtained on land, and with simulations. “Synergy between IBUKI/GOSAT and my recent work on global CO₂ trends using NASA's AIRS satellite instrument”, said Dr. Strow, “should improve both instruments unique view of global greenhouse gases. The very international nature of the IBUKI/GOSAT Science Team has already provided me with new collaborations in this politically relevant field of science." More information on IBUKI can be found at http://www.jaxa.jp/projects/sat/gosat/index_e.html.

Antonia successfully defended her dissertation on November 20, 2008.

TITLE:
Temperature Change And Water Vapor Feedback In The Atmosphere. A Comprehensive Assessment Using The Atmospheric Infrared Sounder Instrument On NASA Aqua Satellite

ABSTRACT:
Global surface temperature has increased ~0.2 degree Celsius per decade in the past 30 years. Observational data recorded from 1850 to 2007 indicate that the warmest 11 years have occurred between 1995 and 2006. The 2007 report of the Intergovernmental Panel on Climate Change concluded that there is a "very high confidence - 95% confidence - that the global average net effect of human activities since 1750 has been one of warming" and that "most of the observed increase in global average temperatures since the mid-20th century is very likely - 90% confidence - due to the observed increase in anthropogenic greenhouse gas concentrations".

Processes in the climate system that can either amplify or dampen the climate response to an external forcing such as an increase in anthropogenic greenhouse gas concentrations, and directly or indirectly affect the Earth's radiation budget at the top of the atmosphere are normally referred to as "climate feedbacks". Among all trace gases, water vapor is the most sensitive to temperature variations. In fact, water vapor absorbs strongly in the vibration-rotation and pure rotation bands at wavelengths in which a large portion of infrared emission occurs at temperature characteristic of the Earth's surface and atmosphere.

In the present study, we exploit the uniform spatial coverage and high vertical resolution of the Atmospheric InfraRed Sounder database of temperature and water vapor profiles to perform a detailed investigation of the covariance between temperature and water vapor. Differently from the previous studies, who only analyzed the overall tropically averaged water vapor and temperature relationship, we make a more comprehensive analysis by investigating this relationship on a local basis. By doing so, we explore the horizontal gradient of this relationship in the tropics, in order to better confine its range of variability and the interplay of the physical processes underneath it. An overall conclusion on the sign and magnitude of the tropical sensitivity to surface temperature variations by mean of water vapor feedback will be assessed.

Jeff successfully defended his dissertation on November 19, 2008.

TITLE:
Displacement Damage-Induced Electrical and Structural Effects in Gallium Arsenide Solar Cells Following Ion Irradiation

ABSTRACT:
For nearly two decades, deviations between experimental data and the nonionizing energy loss (NIEL) have been observed for GaAs devices. In particular, previous data has suggested that electrical parameters associated with GaAs solar cells can follow different energy dependences with NIEL but only at the higher proton energies. In this paper, displacement damage-induced electrical and structural effects in GaAs solar cells were monitored before and after irradiation with various ions. The radiation-induced defects responsible for causing electrical changes were characterized using illuminated current-voltage, deep level transient spectroscopy (DLTS), and electron beam induced current (EBIC) while the structural changes were monitored using transmission electron microscopy (TEM). The EBIC images showed the existence of radiation-induced active recombination volumes or defect clusters after irradiation with high energy protons (E ≥ 10 MeV) and 22 MeV silicon ions, which were not produced by lower energy protons. The TEM images revealed strain related defects that correspond to the same irradiation conditions for which the defect clusters were observed, and therefore, the defects in the TEM images are associated with those observed in the EBIC images. These defects were not observed prior to irradiation so the lattice strain in the material is definitely associated with irradiation-induced lattice defects. HRTEM imaging has shown that the disordered regions are not amorphous but probably most likely a cluster of vacancies and a surrounding region rich in interstitials, which is produced when a large number of neighboring atoms are displaced in collision cascades known as the displacement spike. The formation of the U-band defect as determined by DLTS seems to evolve under the same irradiation conditions as the defects in the images. This very broad U-band peak is consistent with what would be expected from defect clusters. From analyses of the recoil spectra, high energy recoils appear to be responsible for the formation of these disordered regions and these regions are independent of the total displacement damage energy deposited. This study has shown that NIEL scaling is only violated for incident ion energies when the defect clusters are observed.

Andrew successfully defended his dissertation on November 18, 2008.

TITLE:
Step Dynamics and the Morphological Evolution of Nanostructures

ABSTRACT:
Surface diffusion of atoms plays a significant role in the evolution of the shape of a material in the nanoscale regime because it becomes the dominant mechanism for mass transport as the surface area to volume ratio increases. In this dissertation, I present a theoretical study of the shape evolution of a particular nanostructure: the nanowire. At non-zero temperatures, atomic steps are always present on the surface of a nanostructure and their growth and motion causes a change of shape and can cause the wire to break.

I have studied the morphological evolution of nanowires before and after a break develops, the resulting segments of a broken nanowire whose tips are nanoneedles. My approach is to develop and compare a step motion model and atomistic simulations and test them against available experimental data and classical continuum theory. My approach also allowed me to derive the scaling relations and exponents describing the morphological evolution of nanowires and study the microscopic nature of the instability that causes them to break.

Hao successfully defended his thesis proposal on November 14, 2008.

TITLE:
Theoretical Comparison of Optical Approaches to Quantum Logic Gates

ABSTRACT:
Quantum computing has been of intense interest over the last 10 years because of its promising ability to do high-speed factoring and its potential for the efficient simulation of quantum dynamics. It could be implemented in many different ways using optical techniques. A better understanding of the advantages and disadvantages of these approaches would allow the experimental groups working in this area to optimize their choice of experiment and to concentrate on the approaches that are most likely to succeed. We propose to systematically analyze a number of promising optical implementations for quantum logic gates using standard density matrix theory. Basic issues of theoretical comparison of optical approaches to quantum logic gate will be presented here.

Mike successfully defended his masters thesis on October 30, 2008.

TITLE:
Improved Technologies for a Single Photon Source

ABSTRACT:
One of the key requirements for an optical approach to quantum computing is a reliable source of single photons. The efforts of this research have been directed towards improving both the heralding efficiency and heralding rates of a high performance fiber-coupled single photon source based on an ultrafast pulsed beam-like Type-II parametric down conversion (PDC) source. Entangled photons generated from PDC are inherently broadband (many frequencies) and exit the nonlinear crystal at varying angles (different directions). This makes coupling the photons into single-mode fibers, a desirable feature for quantum computing, difficult. In response to these difficulties we have explored applying multi-layered thin film broadband anti-reflection coatings onto the ends of single-mode fibers using the technique of RF Planar Magnetron Sputtering in an effort to increase the coupling efficiency of the beam-like down converted photons. In addition, we have explored theoretically the broadband nature of novel phase matching geometries to increase heralding rates and minimize photon losses. With the ability to tailor coupling fibers to various down conversion sources we hope to increase both the heralding efficiency and heralding rate to levels needed for a broad range of future experiments.

Vincenzo successfully defended his thesis proposal on October 3, 2008.

TITLE:
Gauss Sums Factorization with liquid crystals and optical interference.

ABSTRACT:
The factorization of a large number N is a quite complicated problem, that has a great impact on the computing field and, in particular, in public-key encryption. A more recent approach to factorization, proposed by Schleich, exploits the periodic properties of the Gauss sums. We propose a different implementation of Gauss sums factorization, using liquid crystals and optical interferometry. This scheme allows us to find the factors of any large number N in only one run, exploiting the spectrum of the incoming light. This apparatus is also able, in principle, to reproduce generalized exponential sums of order p. This allows, at the same time, a reduction of the number of resources to the order of 4pp N and to get a better suppression of the so called ghost factors. A future development of this work will consist of a quantum approach to factorization, exploiting the periodicity of the Gauss sums with the use of intanglement. In fact the quantum entanglement has a key role in reducing the number of resources to an order polynomial in logN, which is not achievable classically.

Congratulations go to Physics graduate students Steven Buczkowski and Kimberly Wall for winning the 2007-08 Outstanding Graduate Teaching Assistant of the Year Award! This award acknowledges and recognizes outstanding graduate teaching assistants for their contributions to the teaching mission of the Physics department at UMBC.

Steve and Kim were presented with a plaque and a check for $500 at the Physics Colloquium on September 3, 2008.

Third year Physics graduate student Steven Buczkowski has been selected to receive a NASA Earth and Space Sciences Fellowship. Steven's proposal entitled "Rainbow and Cloud Side Remote Sensing: A Novel Look at Cloud-Aerosol Interaction and Its Effect on Cloud Evolution" was one of 50 proposals accepted, out of 200 received.

A member of the UMBC Atmospheric Physics PhD program, Steven will work with his advisor, Dr. Vanderlei Martins, to characterize and develop retrieval algorithms for a novel suite of visible and infra-red cameras developed by Dr. Martins and his collaborators here and at NASA Goddard Space Flight Center.

Clouds on Earth require some airborne aerosol in order to form but regional enhancements in aerosol load (e.g. from biomass burning, etc) can have a profound effect on their evolution. These effects can range from shifting precipitation patterns to changes in planetary albedo which could influence global climate. Steven's work with Dr. Martins will seek to better understand the influence of aerosol amount and type on cloud development.

Chris successfully defended his masters thesis on August 27, 2008.

TITLE:
Laser System for the Fabrication of Toroidal Microcavities

ABSTRACT:
Toroidal micro-cavities have been shown to be one of the leading types of cavities for use in strong atom-cavity coupling. This property makes these cavities ideal for a range of applications from cavity quantum electrodynamics studies, to development of single photon sources, and quantum information technologies. The purpose of this project was to setup and test a laser facility for the final step in fabricating toroidal micro-cavities. The facility will later be used for production of these cavities for use in ongoing experiments within the UMBC Quantum Information Group.

Justin successfully defended his dissertation on August 25, 2008.

TITLE:
Initial HfO2 Growth on Si(100) and GaAs(100) Substrates using TEMAH+H2O and TDMAH+H2O ALD Processes

ABSTRACT:
Atomic layer deposition (ALD) is a cyclic growth process that is distinguished by a self-limiting, two-step surface reaction that results in precise growth control and high quality, conformal thin films. Due to the continuous downscaling of MOSFET devices, a large interest has recently developed in the ALD of high-κ dielectric materials as gate oxide layers on Si and III-V substrates. The ALD of HfO2 is an established process; however, there is still controversy over the initial growth mechanisms on differently prepared Si surfaces. This motivated a comparison of the nucleation stage of HfO2 films grown on OH- (Si-OH) and H-terminated (Si-H) Si(100) surfaces. Two different ALD chemistries are investigated, including tetrakis[ethylmethylamino]hafnium (Hf[N(CH3)(C2H5)]4), abbreviated as TEMAH, and tetrakis[dimethylamino]hafnium (Hf[N(CH3)2]4, abbreviated as TDMAH. H2O is used as the oxidizing precursor. Deposition temperatures of 250-275°C result in a linear growth per cycle of 1 Å/cycle. Techniques including Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and transmission electron microscopy are used to examine the film interface and initial film growth. HfO2 films are also subjected to post-deposition anneals, and the film morphology is examined with X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy.

GaAs MOSFET devices have long proven elusive due to the lack of a stable native oxide. Recent research into high-κ dielectric materials for use in Si-based devices has presented many new options for insulating layers on GaAs. HfO2 growth on GaAs(100) from a TDMAH+H2O ALD process is studied here. Three different GaAs surface treatments are examined, including buffered oxide etch (BOE), NH4OH, and a simple acetone/methanol wash (to retain the native oxide surface). Initial HfO2 growth on these surfaces is characterized with RBS and SE. The interfacial composition is examined with XPS both before and after HfO2 deposition. Also, an interesting native oxide ‘consumption’ mechanism is investigated, which involves the dissolution of the GaAs native oxide during the ALD process. This project presents the first detailed study of HfO2 growth on GaAs with the TDMAH/H2O ALD chemistry, providing XPS, RBS and SE characterization of early film growth.

Jason Simon, a 4th year PhD student, was selected to receive the Northrop Grumman Graduate Fellowship in Quantum Optics in August.

The Northrop Grumman Fellowship provides an outstanding opportunity for a talented UMBC Physics student to work with a global leader in defense technology while earning his/her PhD. Fellowship support totals $35,000, which includes an annual stipend, tuition and health care benefits, and some travel for one year.

Dr. Ray Hoff, professor of physics and director of the collaborative NASA-UMBC research centers JCET and GEST, was recently named a Fellow of the American Meteorological Society. Hoff’s expertise on air pollution, climate and the atmosphere has been reflected in a prestigious track record of collaborations with and honors from NASA, the Environmental Protection Agency, Environment Canada, the European Economic Community and other earth science organizations. “I'm pleased and honored to have received a society fellowship at the same time as my colleagues,” said Hoff. “UMBC has clearly reached a point where awards and honors are becoming a larger part of the life of the campus. The story of UMBC as a prestigious place to do cutting-edge research is becoming more obvious to our peers and I hope that recognition spreads statewide.”

Robert C. Reno, Associate Professor and Associate Chair of Physics, has made remarkable contributions to the education of UMBC undergraduate and graduate students. During his 33-year teaching career at UMBC, Reno has taught a total number of 160 courses and developed seven original courses, many serving as the foundation of UMBC’s physics program. He redesigned two undergraduate laboratory courses, incorporating computerized data acquisition. In spring 2007, Reno debuted a new honors course that introduces students to advanced experiments using radioactive materials and x-ray generators. His work in the area of peer instruction was one of the first implementations of group learning on campus and the first in the physics department. A recipient of numerous awards, Reno has received two UMBC DRIF/SRIS awards and a U.S. Army Summer Research Fellowship. Reno earned a B.S. in physics from Manhattan College. He also earned his M.A. and Ph.D. in physics from Brandeis University. Dr. Reno was honored at the UMBC Presidential Faculty & Staff Awards Ceremony on April 11, 2007.

UMBC senior physics major Philip Graff will follow the path of science greats Isaac Newton and Stephen Hawking to Cambridge University as the second UMBC student in the past two years to win the Gate Cambridge Scholarship, one of the world’s most selective academic awards.

Graff, who will pursue a Ph.D. in physics, was one of just 45 U.S. winners chosen from more than 600 applicants and 119 finalists. Graff is UMBC’s second consecutive Gates Cambridge Scholar, following alumnus Ian Ralby ‘02, who won in 2007.
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