A simple analytical theory of plasmonic enhancement of optical nonlinearities in various nanoplasmonic structures is developed. It is shown that in simple structures roughly two-to-three order enhancement of effective third order nonlinear susceptibility can be obtain, while in more complicated arrangements of plasmonic dimers and nanoantennae, enhancement can be as high as four-to-five orders of magnitude. At the same time, if one introduces a more practical figure of merit for nonlinearity, as a maximum attainable phase shift per 10dB loss, this phase shift can never exceed a few degrees, thus making photonic switching in metamaterials all but unattainable. This self-contradictory behavior is caused by a combination of inherently low values of nonlinear susceptibility and large loss in the metal. The conclusion is then that nanoplasmonic metamaterials may enhance weak nonlinearities for various sensing applications, but are rather ineffectual in photonic switching and modulation.

Location: Physics Bldg., Room 401

Dusty plasmas are ionized gases in which charged multi-particle systems can be affected by electric and magnetic fields. They are found in a wide range of settings, from astrophysics to semiconductor manufacturing. In general, plasmas are sometimes referred to as the fourth state of matter, because of their high temperature and charge mobility. Dusty plasmas, however, force us to revisit our notion of states of matter given the wide range of temperatures and particle sizes. These can vary typically from 0.01 to 1 eV and 0.1 to 10 eV for the temperature of ions and electrons, respectively, and have charged micron-sized particles with room temperature, all coexisting and interacting in the same system.

In the laboratory, it is possible to create strongly coupled dusty plasmas that form crystalline arrays. These arrays fall in the realm of soft matter and exist within a background plasma that is dilute, resulting in practically undamped dynamics that allows for direct emulation and measurement of atomistic dynamics in solids. At UMBC, a new experimental facility is under construction that will allow us to create dusty plasmas in fluid or crystal form. The setup includes electrodes with adjustable separation and orientation with respect to gravity. The ability to add magnetic fields as high as 10 Tesla is under design. Planned experiments with dusty plasmas include: studies of friction of coefficient in crystals; compression, tension, and shock dynamics; waves with oscillating boundary conditions; and response to fast (> 10 eV) electrons penetrating the crystal lattice.

Location: Physics Bldg., Room 401

Semiconductor nanocrystals and metal nanoparticles are key building blocks for nanophotonics, because they both interact strongly with light in a way that can be tuned by changing the size, shape, and composition of the particles. Light incident on noble-metal nanoparticles excites surface-plasmon resonances, or collective oscillations of conduction electrons, and light incident on semiconductor nanocrystals interactions with excitons, or bound electron-hole pairs. Time-resolved optical measurements on these particles can thus be used to probe electronic, chemical, and mechanical processes on ultrafast time scales and nanometer length scales. I will discuss some examples of the nanoscale physics that can be studied in this way: (1) measurements of charge relaxation, separation, and localization in semiconductor nanoparticles; (2) studies of nanoscale mechanical energy dissipation using plasmons as an optical probe; and (3) new optical properties that emerge from coherent interactions between plasmons in metal nanoparticles and excitons in semiconductor nanoparticles.

Location: Physics Bldg., Room 401

Semiconductor nanocrystals and metal nanoparticles are key building blocks for nanophotonics, because they both interact strongly with light in a way that can be tuned by changing the size, shape, and composition of the particles. Light incident on noble-metal nanoparticles excites surface-plasmon resonances, or collective oscillations of conduction electrons, and light incident on semiconductor nanocrystals interactions with excitons, or bound electron-hole pairs. Time-resolved optical measurements on these particles can thus be used to probe electronic, chemical, and mechanical processes on ultrafast time scales and nanometer length scales. I will discuss some examples of the nanoscale physics that can be studied in this way: (1) measurements of charge relaxation, separation, and localization in semiconductor nanoparticles; (2) studies of nanoscale mechanical energy dissipation using plasmons as an optical probe; and (3) new optical properties that emerge from coherent interactions between plasmons in metal nanoparticles and excitons in semiconductor nanoparticles.

Location: Physics Bldg., Room 401

The cosmic microwave background (CMB) serves as a "backlight" throughout the evolution of the universe, encoding details of physics at energies up to a trillion times higher than any accessible to particle accelerators. New instrumentation now offers the tantalizing possibility of detecting the "smoking gun" signature of primordial inflation through its imprint on the linear polarization of the microwave background. A positive detection would have profound consequences for both cosmology and high-energy physics. It would not only establish inflation as a physical reality, but would probe physics at energies approaching Grand Unification. I will present the scientific motivation behind measurements of the CMB polarization and discuss how recent experimental progress could lead to a detection in the not-very-distant future.

Location: Physics Bldg., Room 401

Inadequate representation of the macrophysical, microphysical and radiative properties of clouds in global circulation models is one of the largest sources of uncertainties in Earth’s climate projections. In the case of radiative properties, in particular those of ice clouds are highly uncertain because of the myriad of ice crystal shapes and sizes that can form and evolve in natural ice clouds. Currently, satellite instruments provide global estimates of two of the three fundamental radiative properties of ice clouds, namely optical thickness and effective ice crystal size near cloud top. However, very little is known about the natural variation of the third fundamental radiative property of ice clouds, the asymmetry parameter, which mainly depends on ice crystal shape. Moreover, current satellite retrievals of ice cloud optical thickness and effective ice crystal size are highly uncertain because they depend on an assumed, fixed asymmetry parameter that does not vary as in nature. In this talk, I will discuss a newly developed technique to simultaneously infer all three fundamental radiative properties of ice clouds from satellite measurements.

I will first explain the relation between the radiative and microphysical properties of ice crystals. I will review the current technique to infer ice cloud optical thickness and crystal size and will show how such retrievals can be greatly enhanced by simultaneous retrievals of the asymmetry parameter using multi-directional polarization measurements. Examples will be shown of this technique applied to detailed aircraft measurements, to satellite measurements over the Tropical West Pacific, and finally to global measurements. The variation of ice crystal size, shape and asymmetry parameter with atmospheric conditions will be discussed.

Location: Physics Bldg., Room 401