Thomas G. Brown, Ph.D. - US grants

The requested electrochemical profiler/photovoltage spectroscopy unit brings new capabilities to the recently established optoelectronics facility at the Institute of Optics, for epitaxial growth, characterization and fabrication of III-V heterstructure optoelectronics devices. The profile/photovoltage instrumentation is required for many aspects of an extensive research program that includes the investigation of quantum well lasers and modulators grown on (111) substrates (for low threshold and higher modulation frequency lasers, and larger electro-optic effect), quantum well lasers with doped active regions (for higher gain), novel circularly symmetric surface emitting laser structures, pseudomorphic GaInAs quantum well lasers (for lasing in the wavelength range of 860 to 110 nm., a region previously inaccessible to high efficiency diode lasers), quantum well lasers structures with dry etched facets (to enable integration of diode lasers), fast electro-optic modulators (for high speed phase and intensity modulation of light), an innovative approach to the disordering of superlattices by impurity diffusions (using applied electric fields during annealing) and the use of such selectively disordered structures in planar optical structures (lasers, waveguides, gratings electro-optic modulators). These research programs compliment the ongoing effort in indirect bandgap semiconductors (isoelectronic impurity complexes in indirect bandgap semiconductors, low noise avalanche photodiodes and nonlinear optical interactions in silicon on insulator structures), also at the Institute of Optics. The facility for growth, characterization and device fabrication of optoelectronic III-V semiconductors presently includes a molecular beam epitaxy machine, Raman, photoluminescence and excitation spectroscopy, photolithography, chemically assisted ion beam etching and rapid thermal annealing. The electrochemical profiler and photovoltage spectroscopy unit will be used to measure carrier concentration and bandgap profiles in III-V and Si state of the art optoelectronic materials and devices.

WPCf 2 B J d | x MACNormal p 5 X ` h p x (# % '0* , .81 3 5@8 : < : } D 4 P T I. A. 1. a.(1)(a) i) a) T 0 * * . , US X ` h p x (# % '0* , .81 3 5@8 : < : } D 4 P 0 * * . , US , 3 ' 1 Z MACNormal Hall 9311044 The Institute of Optics at the University of Rochester will purchase a pulsed laser system and an electron beam deposition unit that will be dedicated to support r esearch in engineering. The equipment will be used for several research projects, including in particular: 1)the fabrication and investigation of circularly symmetric grating, surface emitting semiconductor lasers, 2) new materials and epitaxial structures for advanced semiconductor lasers, 3) epitaxial layer disordering in III V Heterostructures, and 4) avalanche processes in semiconductors and gain coupled semiconductor lasers for applications in optoelectronics. ***

The proposal research is to investigate fundamental issues regarding long fiber Bragg gratings in two important areas: first, the stabilization of the fabrication process by a new approach for real-time adaptive grating writing, and second, the methodology of synthesis of long gratings based on inverse scattering method for optimum design. Both of these are important issues that are holding back progress in the field. The fiber Bragg gratings have a broad impact on optical communications, particularly on dispersion management, and optical pulse shaping.

This GOALI award, co-funded by the Division of Materials Research and the Office of Multidisciplinary Activities of the Directorate for Mathematical & Physical Sciences, involves a collaboration between the University of Rochester and the Eastman Kodak Company. A new concept for photoresponsive polymers is described based on a process called Quantum Amplified Isomerization (QAI). QAI materials are defined as polymers that undergo electron transfer-initiated ion radical chain isomerization reactions upon absorption of light. QAI materials have the potential to overcome many of the known problems associated with existing photoresponsive polymers, while still retaining their primary advantages. Specifically, QAI materials are designed to produce many chemical tranformations per photon absorbed, with little or no accompanying dimensional changes. The primary research goals of this proposal are: (1) to obtain a predictive understanding of the fundamental ion radical chain reaction chemistry that forms the basis of QAI processes, (2) to test sensitization strategies for the efficient inititaion of QAI processes, (3) to use the insights from (1) and (2) to design and synthesize functionalized QAI polymers, and (3) to characterize key optical properties of new QAI materials.

This collaboration is in the fields of photochemistry and optical materials for communications, and involves a number of educational experiences, including on-site industrial research for the students and weekly group meetings among the academic and industrial co-PI's.

0076322
Houde-Walter

The Institute of Optics at the University of Rochester is building an excitation spectroscopy laboratory for research in new optical sources utilizing nano-engineered optical materials. An optical parametric oscillator, monochromator and multiscaler will be used in four research programs and two undergraduate/graduate training labs. Energy transfer will be studied using excitation spectroscopy to refine laser rate equation models and help to determine the best host composition and doping levels in rare-earth doped nano-glasses. In a related teaching lab exercise, students will observe cooperative luminescence in Yb-doped glasses, as is currently practiced in optical amplifier research. In another project, radiative impurity complexes will be introduced into silicon-on-insulator (SOI) structures that exhibit enhanced absorption/emission via nanostructured surfaces. Excitation spectroscopy will be used to elucidate the microscopic processes that determine emission cross sections in the hybridized SOI structures. Photoluminescence (PL) spectroscopy will be used to explore phonon mode control in isotopically pure crystalline Si. The new lab will permit the excitation of high spatial densities of indirect excitons, which may result in coherent phonon emission. Group III-V quantum dots, as made by in-situ laser patterning during molecular-beam epitaxial (MBE) growth, will also be investigated. Resonant excitation will be used to probe quantum dots of very narrow size distributions and may indicate the limit of what might be eventually achieved with an ensemble of uniform features. In a related lab, undergraduate students will investigate the absorption spectra of bulk crystals with various bandgaps (Si or GaAs, GaP, and GaN or diamond) as well as quantum well and dot group III-V semiconductors grown in our MBE lab. Honors students will also be encouraged to use the new lab for independent projects during their senior year.
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The Institute of Optics at the University of Rochester, which grants Bachelors, Masters and doctoral degrees in Optical Science and Engineering, is building a new optical spectroscopy lab for research and training. New optical materials that utilize features on the nanometer (one billionth of
a meter) scale, will be emphasized. New training exercises that are closely related to this research will be offered to both undergraduate seniors and first-year graduate students. A tunable source and associated detection equipment will be used to probe the relationships between the microscopic components and their radiative efficiency. Improved knowledge and design of materials for many applications, including biomedical research and telecommunications, are expected. However, the overarching goal of this new laboratory is to reveal fundamental relations and elucidate hidden connections in the characterization and process parameters of new (or just useful) optical materials.
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Illumination with beams of light in unconventional polarization states departs from the usual, textbook description. Two popular examples of unconventional polarization states are radial and azimuthal polarizations (sometimes called Cylindrical Vector Beams). A wide variety of unconventional polarizations exist -- some have been well studied, while many remain unexplored. This research activity brings together three investigators that have been studying unconventional polarization states and their mathematical representation, the propagation and focusing of polarized light, and light scattering from small particles such as those found within biological cells.

This investigation makes use of a novel mathematical representation (complex-focus basis) for modeling optical focusing and scattering, the study of radial, azimuthal, and Full Poincare fields as representatives of a complex-focus basis, and the scattering of unconventional polarization states from mesoscopic particles, including cell organelles. In the process, we also address the formulation and testing of a theory of partially coherent unconventional polarization states, the coupling of unconventional polarization states to nanostructures, and develop numerically efficient theoretical models for coherent and partially coherent light propagation. We make use of the recently-introduced concept of stress- engineered optical elements to adapt an existing light scattering microscope to carry out polarization- sensitive scattering experiments. In the process, we are advancing optical physics by introducing new analytic tools for scattering analysis, a new experimental tool for rapid-acquisition pupil polarimetry, and find better ways to use polarization as a tool for improving projection imaging systems such as LCD projectors and semiconductor lithography systems.

Polarization--the vector nature of light--influences the scattering of light in profound ways, and is therefore fundamental to how we gain information about a scatterer from the scattered light. This has been used to good result in advancing cell identification for immune cell research, for example. Scattering is also important in the inspection processes that are used to guarantee high quality semiconductor circuits for computers and electronic devices. A better understanding of the physics of new polarization states will therefore have a broad impact on fields such as optical engineering and biomedical optics. The educational impact is seen annually through involvement by both undergraduates and graduate students, not merely as research assistants, but as students in training who are encouraged toward independent initiatives. Our role as educators at the Institute of Optics offers us a unique platform from which to take the results of the work, bring them into the classroom at the MS and BS levels, and to take the exciting features of polarized light with us on educational activities in area schools and science museums. Our presence at the Institute of Optics offers technology transfer to over 30 companies who are members of our Industrial Associates Program.

Polarized light (light with directional vibrations whose effects can sometimes be seen in changes in attenuation while rotating polarizing sunglasses) is everywhere--it is in the blue sky, the reflection from a pond, in light scattering from natural and manmade airborne particles, and in the display screens on our smartphones. The understanding and use of polarized light is central to both the science of light and to applications ranging from medicine to consumer electronics. For example, some of the triumphs of the computer information revolution have been built around manufacturing technologies that require almost unimaginable precision in measurements--many of which are light-based and use the polarization of light in ways that can be precisely controlled and measured. The proposed research uses the concept of an "unconventional polarization state" - a special form of light in which the polarization varies across the width of a laser beam - to explore fundamentally new ways of carrying out light-based measurements. In conjunction with some special optical devices, it is possible to use an ordinary camera to create a visual map of the polarization in a single image, something that ordinarily requires a sequence of four or more images and accompanying algorithms. These measurement methods will also spur new ways of thinking about how to execute the simultaneous measurement of sub-nanometer process errors in microelectronics manufacturing.

The multiple measurements required to characterize the polarization of an ultrafast laser pulse or individual photon require either a time-sequential operation or explicit division of the amplitude into different detector ports. While each of these has been used to good success, there is a need to truly extend polarization measurements in a way that the maximum amount of polarization information is extracted from each measured photon (in the case of low light levels) or each pulse (in the case of ultrafast pulse characterization). Because the method is extendable to the mapping of polarization over a sampled image field, it is possible to extend the concept to capture either angle- or frequency-resolved polarization information in a single image. The investigation also applies the new physics of unconventional polarization states to the now-famous physics of weak measurements by using unconventionally polarized light to measure two or more physical quantities in a single measurement. This concept will be tested by measuring nanoscale features in a microscope equipped with a liquid crystal controller that defines a field with arbitrary polarization, amplitude, and phase for focused beam scatterometry. The work is expected to impact allied areas of physics (through the introduction of new measurement methods), optical engineering (specifically, polarization engineering and image formation), biomedical optics (in medical imaging and spectroscopy), environmental science (through the use of polarimetric light scattering for aerosol characterization), and semiconductor inspection.