A study of photoconductive switching phenomena and an application in ultrafast electrical pulse shaping

This dissertation discusses some new developments in research and application of photoconductive semiconductor switches. How the dynamic response to laser illumination uniformity affects high-power GaAs photoconductive switching is studied. In linear switching operation, the electric fields within the switch redistribute themselves immediately after optical illumination. Asymmetric illumination creates a high field region on the nonilluminated side in about 100 ps. Illumination at the cathode compresses the field toward the anode, and illumination at the anode compresses the field toward the cathode. The nonlinear switching behaviors of GaAs photoconductive switches are investigated over a longer time scale. A nonlinear mode of repetitive-current-spikes was first observed in the experiment. The period for the repetitive-current-spikes is about 70-75 ns, or 13-14 MHz in frequency for a 6.9-mm long GaAs sample. The experiments suggest that Gunn oscillation could be a reason of this nonlinear switching mode.; A transmission-line discrete-circuit model was established to simulate the dynamic behavior of laser illumination uniformity in high-power GaAs photo-conductive switches. There is a good agreement between the theoretical predictions and the experimental results.; A new conceptual method for sharpening the leading edge of an ultrafast electrical pulse is comprehensively studied in this dissertation. A relativistic moving ionization front induced by a ultrafast optical pulse with tilted-wave-front has been experimentally proven to shape an incoming electrical pulse. The leading edge of the pulse was sharpened more than 30%. The experiments also confirmed that the degree of sharpening is determined by the speed of the ionization front. A very important result of these experiments is that the output electrical signal frequency, which corresponds to the rise time of electrical pulse leading edge, could be tuned by changing speed of the ionization front. When the speed of the moving ionization front increases by {dollar}sim{dollar}33%, the detected pulse rise time decreases {dollar}sim{dollar}30%. Theoretical simulations based on transmission line circuit model generally agree with the results of the experiments.; To detect the single-shot ultrafast electrical signal, a novel technique was developed to characterize such electrical pulses. In this method, a streak camera is used to image the temporal evolution of the surface electric field leading edge of the electrical pulse via the electro-optic effect. The streak camera imaging of the electrical pulse has increased the detection resolution to about 2 picoseconds even though the probe pulse had a duration of {dollar}sim{dollar}60 ps.