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About October 2011

This page contains all entries posted to Physics Announcements in October 2011. They are listed from oldest to newest.

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October 2011 Archives

October 5, 2011

Seminar: Wednesday, Oct. 5, 2011 at 3:30pm

Pictures, Models, Approximations and Reality:
Phase transitions and our understanding of the physical world
Dr. Michael Fisher
UMCP, Institute for Physical Science and Technology

Ways in which theoretical physicists look at the real world and try to understand it will be explored. Through the medium of a domino game on a large checkerboard, the rapier-like specific heat of a superfluid helium, and the visual effects seen when a liquid and its vapor merge to form a supercritical fluid, the talk will address the question: "What is the role of the theorist in modern science?" The power of analogy based on physical pictures and simple models will be illustrated in the context of ideas concerning phase transitions and critical phenomena in fluids and magnets, in alloys and plasmas. The significance of the concepts of shape and singularity in the search for universality will be explained; the role of symmetry and dimensionality in our insights will be touched upon.


Location: Physics Bldg., Room 401

October 6, 2011

PhD Proposal - Anthony Davidson

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.


October 11, 2011

PhD Proposal - Amanda Dotson

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.


PhD Defense - Aboubakar Traore

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.

October 12, 2011

Seminar: Wednesday, Oct. 12, 2011 at 3:30pm

Beyond the Rayleigh limit in optical lithography
Dr. M. Suhail Zubairy
Texas A&M University
Institute for Quantum Studies and Department of Physics and Astronomy

It is well known that the classical schemes for microscopy and lithography are restricted by the diffraction limit. The precision with which a pattern could be etched in interference lithography is limited by the wavelength of the light. In recent years, a number of schemes have been proposed via quantum interferometry to improve the resolution. Some of these schemes are based on quantum entanglement and multiphoton processes. In this talk we shall discuss several schemes for 'quantum' lithography using classical light.


Location: Physics Bldg., Room 401

October 19, 2011

Seminar: Wednesday, Oct 19, 2011 at 3:30 pm

New frontiers with ultra-cold molecules.
Paul S. Julienne
Joint Quantum Institute
NIST and the University of Maryland

Cold atoms have proved to be a highly successful workhorse for research in experimental and theoretical physics for over two decades now, touching on diverse areas such as atomic and molecular physics, precision measurement, condensed matter physics, and quantum information and computing. Recent developments in producing cold and ultra-cold molecules promise to open up many new aspects of studies with ultra-cold matter with temperature in the nanokelvin range. Molecules are much harder to cool and trap than atoms, because of their much more complex internal energy level structure of vibration and rotation. On the other hand, molecules can have relatively large dipole moments and consequently new ways of controlling and interacting them not available with atoms. This talk will review progress in making and using cold molecules, emphasizing the assembly of an ultra-cold molecule in its ground state from two already ultra-cold atoms. The quantum dynamics that determines the chemical reactions of two such molecules with nearly zero kinetic energy turns out in some cases to have a remarkably simple universal character, subject to experimental control using the bosonic or fermionic nature of the molecules or using electric fields to orient the molecules in various kinds of optical traps or lattices.

Location: Physics Bldg., Room 401

October 26, 2011

Seminar: Wednesday, Oct. 26, 2011 at 3:30pm

FASTā€CARS
Dr. George Welch
Texas A&M University

The vibrational structure of a molecule can be a useful signature or "fingerprint" of a substance. Inelastic scattering of light by molecules is an important tool for probing molecular vibrational structure. Thus, inelastic scattering of light from molecules can be a useful method for detecting particular molecular species. This effect is called Raman scattering after Chandrasekhara Venkata Raman, who received the 1930 Nobel Prize in Physics for its discovery.

The Raman effect is typically very weak, and coherence is a very powerful way to produce larger signals. Multiple photons can be used to excite and scatter from molecular vibrations, resulting in a signal that is sensitive to the same vibrations as in Raman scattering, but where the fields emitted from all molecules can add coherently, producing a very large signal that is quadratic in the number of scattering molecules. This effect is called coherent anti-Stokes Raman scattering, or CARS.

CARS is a third-order nonlinear optical process and may be masked by other nonlinear optical processes, such as four-wave mixing. Also, because of its large quadratic dependence, CARS may be unsuitable for detection of small amounts of a substance in the presence of a large background o other molecules.

There are many approaches for resolving the problems of CARS while preserving its high signal level. One method is to use femtosecond lasers with temporally shaped pulses to exploit the vibrational structure of molecules. We refer to these tricks as "FAST-CARS" for "femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman scattering".

I will introduce all these concepts, and present many results from various experiments we have performed over the last few years. I will also show how optical interference can be used for broad-band heterodyne detection of FAST-CARS signals, giving rise to interesting new effects.


Location: Physics Bldg., Room 401

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