Femtosecond Optics of Quantum Confined Materials and Devices

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This project is directed towards basic understanding of quantum confined semiconductor optical nonlinearities and demonstration of high-speed all-optical devices. The materials that will be investigated under this program are Cadmium Selenide and Cadmium Sulfide quantum dots and GaAs - A1GaAs multiple quantum wells. By quantum dots, the investigators mean microcrystals of semiconductor embedded in glass matrices with sizes that are comparable or smaller than the exciton Bohr radius with a more uniform size distribution. They will investigate thoroughly the magnitude and response time of optical nonlinearity in these quantum dots and compare these quantities with their bulk values, will enable them to determine whether quantum confinement in the dots results in enhancement of the nonlinearity or speed of the material. The instantaneous nonlinearity arising from exciton optical Stark effect will be employed to demonstrate high-speed switching in a GaAs MQW directional coupler. Finally, they will attempt to generate subpicosecond electrical pulses using virtual carrier excitation, and then use these ultrashort electrical pulses to obtain subpicosecond switching in a MQW nonlinear directional coupler via the quantum confined Stark effect.