College of Optical Sciences News for Thursday, September 21, 2006

Today:  September 21, 2006 -- OSC Colloquium -- 3:30 p.m. -- Meinel 307
Professor Roland Zimmerman, Humboldt University, will present Bose-Einstein Condensation of Excitons: Promise and Disappointment.  Professor Galina Khitrova and Professor Hyatt Gibbs are the hosts.  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.

Coming Up:  September 22, 2006 -- OSC Community Speakers -- Noon -- Meinel 307
(1)  Zhipeng Wang will present Analyzing Spectral Sensors with Overlapping Bands.  Description: Some spectral sensors have significant overlap in the spectral responses of their different bands.  An example is the human eye.  Data interpretation is relatively difficult for these sensors.  Here we consider the spectral imaging process as a projection, in the spectral domain, from the scene to a sensor space and analyze the influence of band overlap through that. In this presentation, the projection model is applied to color science to explain color vision.  Although the title of this talk is from the remote sensing area, people with interest or background in color theory are encouraged to attend.

(2)  Jim Wyant will present The Excitement of Starting and Growing a Company. 
For more information about the OSC Community Speakers, please visit http://www.optics.arizona.edu/communityspeakers/

Coming Up:  September 22, 2006 -- Physics Colloquium -- 2:30 p.m. -- PAS 220
(1)  2:30 p.m. -- Graduate Student Cory Christenson will present Climbing the Jaynes-Cummings Ladder.  Abstract:  Cavity QED experiments have been performed with a quantum dot in a photonic crystal slab nanocavity. When a two-level atom strongly couples to a resonant electric field inside a cavity, the dipole moment interaction creates a "ladder" of doublet energy states. In this case, the atom is a quantum dot and the cavity is a photonic crystal. The lowest rung has been seen, but observations of higher rungs would prove the system is truly quantum and allow us to probe the quantum-classical boundary.

(2)  3:00 p.m.  Victor Klimov, Los Alamos National Laboratory, will present Fundamental Photophysics of Multiexcitons in Semiconductor Nanocrystals from the Perspective of Solar Energy Conversion.  Abstract:  We have recently demonstrated that nanocrystal quantum dots can efficiently produce multiple electron-hole pairs (excitons) in response to a single absorbed photon. To address the generality of this carrier-multiplication phenomenon in nanocrystalline materials, we performed a comparative study of multiexciton generation in PbSe, PbS and CdSe quantum dots that have distinctly different electronic structures. We found that all systems exhibit high-efficiency carrier multiplication, resulting in up to 700% quantum efficiency for photon-to-exciton conversion. As expected from simple effective-mass arguments, the activation threshold for this phenomenon is lower in CdSe nanocrystals than in PbSe and PbS nanocrystals (ca. 2.5 vs. 2.9 energy gaps). Interestingly, the efficiencies of multiexciton generation are nearly identical for both lead and cadmium salts despite the vast difference in energy structures and carrier relaxation behavior, strongly suggesting that this phenomenon is general to nanocrystal quantum dots. We propose a model for the observed carrier multiplication, within which direct (instantaneous) photo-generation of multiexcitons occurs via virtual single-exciton states.

Coming Up:  September 22, 2006 -- Sports Friday -- 5:00 p.m. -- Location is TBD

Coming Up:  September 25, 2006 -- BME Seminar -- 2:00 p.m. -- AHSC 5403

Kathleen Perkins, William Donnelly, and Paul Holcomb, all of Breault Research Organization, will present ASAP Optical Software: A Value Tool for Biomedical Research and Product Innovation. Abstract: Product innovation is happening all over the world but Tucson, as "Optics Valley", remains special to the mix. Hundreds of optical technology companies have made their homes here and the University of Arizona is a renowned center of excellence in optical engineering. Breault Research Organization (BRO), an optical engineering firm, facilitates strong ties between academic and commercial entities and provides solutions in the form of cutting-edge optical design software, education, and engineering services.  In this seminar Ms. Kathleen Perkins (CEO) will describe the company, its business and educational relationships, and discuss some of the hurdles of turning ideas into products -- including business plans, the language of business, pitching ideas to venture capitalists, and the local and national landscape of funding sources.  A technical overview of state-of-the-art software products for biomedical research will follow with a focus towards the biomedical research community.  Dr. William Donnelly will present trends in optometric and ophthalmic patients. ASAP software will be demonstrated as a virtual phoropter, as a simulation test bed for cataract and intraocular optics, and as a mechanism for binocular vision research and other clinical applications. We will also highlight ASAP optical modeling by engineer Paul Holcomb demonstrating the penetration of skin by radiation. Using ASAP, optical radiation devices can be developed for treatment techniques such as photodynamic therapy.  Additional modeling capabilities of ASAP will be shown in the form of a urinary bladder, an MRI application, a sensor attached to a finger, fluorescence, and a scanning microscope.

Coming Up:  September 27, 2006 -- Practical Optics Seminar -- 2:00 p.m. -- Meinel 305

Jim Burge will present a talk on telescope optics.  Everyone with an interest is invited to attend.  No advance registration is needed.

Sine Curve Sculpture on Display at Pima Council on Aging

The next time you take Broadway out to the far east side, stop for a moment at the Pima Council on Aging (8467 East Broadway) to admire Professor Emeritus Stephen Jacobs' elegant sine curve sculpture in the atrium.  The 8-foot tall sculpture is made from a single rectangular sheet of polystyrene, folded along four sine curves.  Steve's sine curve sculptures vary in size and shape and are beginning to catch on, so in response to popular demand, Steve has developed a workshop for high school math students in which students create their own sine curve sculptures and take them home afterward.  He recently conducted 45-minute workshops at Tucson City High and Tucson Design College and is available to other organizations as well.  Call him at 520-621-2944 or send an e-mail to stephen.jacobs@optics.arizona.edu  The photo is a thumbnail, so give it a click for a larger view.

The Mt. Graham Trip

Thanks to our Student Optics Chapter and Ben Richards, some 70 Optical Sciences students, faculty, and staff visited Mt. Graham and toured the Large Binocular Telescope this weekend.  Thank you also to John Greivenkamp, Rick Shoemaker, and Julian Sweet for contributing an abundance of photos.