U.S.-Federal Republic of Germany Cooperative Research: Nonlinear Optical Properties of Microstructures and Femtosecond Phenomena in Semiconductors

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This award will enable Dr. Nasser Peyghambarian and Dr. Stephen W. Koch. University of Arizona, to collaborate with Dr. Hartmut Haug, University of Frankfurt, Federal Republic of Germany. They are carrying out experimental and theoretical studies of quantum confinement effects and short pulse phenomena in semiconductor micro-structures. Experimental work will include a study of the dynamics of highly excited semiconductors and semiconductor micro-structures using femtosecond laser excitation. They will induce gaps in semiconductor bands with light, and they will measure the evolution of the spectral hole and carrier thermalization process. They will also investigate nonlinear optical properties of semiconductor quantum-dots using semiconductor micro-crystallite doped glasses and etched micro-structures. The researchers' theoretical studies will examine the linear and nonlinear optical properties of semiconductor micro-structures and analyze quantum confinement effects. They will also study coherent processes and high-field effects in semiconductors with non-equilibrium Green functions and quantum-mechanical rate theories. They will investigate ac-Stark splitting of semiconductor bands caused by a strong external field and they will compute the dynamics of the nonequilibrium carrier distribution. A semiconductor under strong optical excitation is an ideal system to study nonlinear and non equilibrium processes of high current interest in solid state physics. The purpose of the research is to study the basic phenomena associated with nonlinear interactions between light waves and a variety of materials, most notably semiconductors with reduced space dimensions. Dr. Peyghambarian has done many of the experimental studies relevant to this research using a state of the art femtosecond laser system in his laboratory. Dr. Koch and Dr. Haug provide strong complementary theoretical expertise for the collaboration. The research is important for understanding fundamental physical phenomena which have potential applications in optical signal processing.