Fall 2006 Colloquium

Speaker:

Nasser Peyghambarian, College of Optical Sciences, University of Arizona

Title:

Photonic Materials and Devices

Host:

Stanley Pau

Abstract:

Our recent advances in solid-state optoelectronic materials and devices will be reviewed. In the area of glass optics, fabrication of novel microstructured and multi-core fibers and their use in realizing single mode lasers will be summarized. In organic and plastic optics, photorefractive polymers for 3D display applications and nonlinear polymers for high speed modulators in RF photonic and remote antenna applications will be discussed. Our progress in medical optics including adaptive eyewear and imaging will also be described.

Speaker:

Grover Swartzlander, College of Optical Sciences, University of Arizona

Title:

Searching for Extrasolar Planets with an Optical Vortex Coronagraph

Host:

Stanley Pau

Abstract:

When inserted in a coronagraph, an optical vortex lens has the potential to  resolve a profound question:  Are we alone in the Universe?  This talk will discuss my group's experimental and theoretical progress.  Our upcoming experiment, being designed in collaboration with Steward Observatory and the Jet Propulsion Laboratory,  will also be described.

Speaker:

Roland Zimmerman, Humboldt University

Title:

Bose-Einstein Condensation of Excitons: Promise and Disappointment

Hosts:

Galina Khitrova and Hyatt Gibbs

Abstract:

Excitons in semiconductors have been considered for quite a long time as possible candidates for observing Bose-Einstein condensation. Due to their rather light mass compared with atoms, a much higher critical temperature can be expected in principle. However, other properties are disadvantageous: The finite lifetime of excitons hinders equilibration at low temperatures, and the strong exciton-exciton repulsion acts against condensation. In addition, at high densities, excitons may break off into electron-hole pairs (Mott transition).  In the talk, different excitonic systems are discussed which have been explored in view of  condensation: Zero-bandgap semiconductors, polaritons in microcavities, and dipole-forbidden excitons. Special emphasis is given to spatially indirect excitons in coupled quantum wells. A dynamical T matrix theory is presented which allows to explain recent experimental results (blue shift and spectral broadening) of the excitonic emission in a lateral trap. Spectral and angular characteristics of the emission may serve as indicator on the way towards condensation.

Speaker:

Martin Tomasko, Lunar and Planetary Laboratory, University of Arizona

Title:

Images and Spectra Obtained in Titan's Atmosphere and their Implications for the Properties of Titan's Aerosols and Surface

Host:

Stanley Pau

Abstract:

On January 14, 2005 the Huygens Probe descended through the atmosphere of Titan and landed on the surface.  The Descent Imager/Spectral Radiometer (DISR) instrument aboard the probe collected data from 140 km altitude to the surface including images of the surface, spectra of solar radiation from 350 to 1600 nm looking upward and downward in many directions, and images of the solar aureole at 490 and 940 nm in two directions of linear polarization.  The images have been assembled into panoramic mosaics extending from 0 to 96o nadir angles.  A video has been made showing the descent through the atmosphere toward a highland cut by steep dendritic drainage channels and a dry lakebed that shows evidence of fluid flow.  These images and those obtained on the surface after landing showing rounded cobbles in the dry lakebed imply the presence of occasionally heavy methane rain on Titan.  The spectra of solar radiation obtained throughout the atmosphere together with the measurements of the solar aureole yield the vertical distribution and variation with wavelength of the optical properties of the aerosols present in the atmosphere.  The high degree of linear polarization and the strong forward scattering measured by the solar aureole imply that above 80 km altitude the haze aerosols consist of loose aggregates of some 400 “monomers” of radius less than 0.05mm.  The upward and downward spectral measurements imply that above 80 km the cumulative optical depth of these particles decreases with a scale height of 65 km.  From 80 km to 30 km altitude, the optical depth of the aerosols varies linearly with height, the optical depth of the aerosols varies less rapidly with wavelength, and the particles are much less absorbing, implying that other material, most likely liquid ethane, has been incorporated into these particles.  In the lowest 30 km, the optical depth of the aerosols varies linearly at a different rate, the optical depth varies much less rapidly with wavelength, and the particles are not very absorbing, implying that liquid (and/or solid) methane has been incorporated into the particles.  Indeed, some recent work suggests that the probe landed in a region of light methane drizzle.

Speaker:

Majeed M. Hayat, Department of Electrical and Computer Engineering, Center for High Technology Materials, University of New Mexico

Title:

Forty Years Since McIntyre's Avalanche Multiplication Theory: Current Implications on Ultrafast Receivers and Single-Photon Detection

Host:

Scott Tyo

Abstract:

In 1966, R. J. McIntyre published key results that shed light on the mathematics of avalanche multiplication in semiconductors, which helped answer many questions on the extent of use of avalanche photodiodes in amplifying weak optical signals in two modalities: linear (or intensity) mode and photon-counting mode, also known as Geiger mode. The fundamental question is which materials lend themselves to avalanche photodiodes for which the desirable gain factor, offered by avalanche multiplication, outweighs the excess noise and reduced speed that result from the stochastic nature of the very process of avalanche multiplication that generates the gain.   Since McIntyre’s original work, there have been new findings on avalanche multiplication in thin layers, both from physical and mathematical perspectives, which have changed our understanding of how avalanche multiplication really works and how it should be exploited in linear- and Geiger-mode applications. One of the key findings is the so-called dead-space effect, to which the good performance of many modern avalanche photodiodes has been attributed.  Proper understanding of the dead-space effect, however, required the development of new non-Markovian analytical models for avalanche multiplication. In this talk I will highlight the mathematical and physical attributes of avalanche multiplication in semiconductor materials and devices while describing their capabilities and limitations. I will also present examples of novel avalanche photodiodes both for linear- and Geiger-mode detection in the near-infrared to longwave-infrared regimes. Finally, I will present novel equalization strategies that can be used to enhance the performance of avalanche photodiodes to a level that is potentially attractive for next-generation optical receivers. 

Speaker:

Alfred McEwen, Department of Planetary Sciences, University of Arizona

Title:

Early Results From MRO/HiRISE

Host:

Nasser Peyghambarian

Abstract:

The High Resolution Imaging Science Experiment (HiRISE) is a digital camera with the largest telescope to ever leave Earth’s orbit.  The major developmental challenge was the speed of the focal-plane electronics, required to collect up to 28 Gbits of data in a few seconds.  HiRISE uses Time Delay Integration (TDI) to increase signal to adequate levels while the IFOV is only 1 microradian and the groundtrack speed is ~3.2 km/s.  Mars Reconnaissance Orbiter (MRO) was launched in August 2005, arrived at Mars in March 2006, and completed aerobraking in September 2006.  HiRISE acquired 8 high-altitude images of Mars at ~2-3 m/pixel scale soon after orbit insertion in March 2006, and is expected to acquire ~50 images in early October at ~0.3-1.2 m/pixel in the 3 PM mapping orbit.  Each image consists of data from up to 14 CCD detectors and could contain as many as 3 giga-pixels.   The 8 early images have been useful for development and testing of processing techniques such as radiometric and geometric corrections and color registration. The most recent images will cover a broad range of targets, including past landing sites, the candidate landing regions for the Phoenix mission, a few candidate landing sites for MSL, the north polar cap, layered sedimentary deposits, gullies, and a wide variety of other features of interest.   We expect the stereo and color observations to be especially interesting.  Preliminary science interpretations of these anticipated observations will be presented.  The HiRISE Operation Center (HiROC) is located in Sonett Space Sciences on the corner of University and Cherry Dr. 

Speaker:

Bruce Dunn, Department of Materials Science and Engineering, University of California, Los Angeles

Title:

Optical Biosensors Based on Sol-Gel Encapsulation Methods

Host:

Stanley Pau

Abstract:

The flexible solution chemistry of the sol-gel process has been used to synthesize nanostructured materials based on the encapsulation of biomolecules in a transparent, inorganic matrix. It is now well established that the dopant biomolecules are immobilized in the mesoporous network and become part of the nanostructured architecture of the material.  In nearly all cases, the dopant biomolecules retain their spectroscopic properties and biological activity.  The resulting bio-hybrid materials have been widely explored as sensors with the biomolecule serving as both the biorecognition and transduction elements while the transparency of the matrix enables spectroscopic monitoring of the reactions.  In this presentation I will discuss our recent research on various biosensors for health monitoring.  One example is the use of immunoassay approaches where we have developed a thin film optical biosensor for cortisol, a steroid hormone which is one of the principal biomarkers for monitoring astronaut health.  I will also review related research where we are moving beyond the encapsulation of individual proteins and developing nanostructured systems and multi-functional materials.  The example to be discussed here is the use of a liposome/sol-gel architecture in which photo-induced proton pumping is able to generate ATP.