Electrooptic imaging of surface electric fields in high-power photoconductive switches

A two-dimensional electrooptic probe was used to image the electric field in high-power photoconductive switches during switch operation. A LiTaO₃ crystal, covering the entire active area of the photoconductive switch, coupled the surface electric field with the polarization of an optical probe pulse. The optical probe was imaged onto a two-dimensional detector array, producing snapshots of the surface field with 200-ps time resolution and 3-μm spatial resolution. The probe system was used to monitor the electric field in the electrode gap of high-voltage switches, the focus of investigation being the collapse of the electric field in a GaAs bulk switch as it was switched with a λ=1.06 μm optical pulse. The switching speed and generation of field enhancements were found to be dependent on the illumination configuration and the applied electric field, which varied from 0 to 15 kV/cm. Switching efficiency was found to decrease with increasing field