Optically-activated GaAs switches for compact accelerators and short pulse sensors

This paper describes research and development of high gain GaAs photoconductive semiconductor switches (PCSS) for two very different types of applications: compact, repetitive accelerators and short pulse, active optical sensors. The accelerator is being tested with a spark gap driven modulator. It is a short pulse, linear induction accelerator (LIA) with an electron diode. Its design goals are: 700 kV, 7 kA, 30 ns pulses at 50 Hz. After characterizing the accelerator with the spark gap modulator, it will be tested with a GaAs PCSS modulator, which is under construction. Forty-eight, 2 inch diameter PCSS will switch 70 kA in a 250 kV coaxial Blumlein to deliver 220 kV, 35 kA, 30 ns pulses to the LIA. One module (1/8^th) of the PCSS modulator is being tested. Results from these tests and projections for the complete system are discussed. The short pulse sensors are for military and commercial applications in optical and electrical range sensing, 3D laser radar, and high speed photography. The highest optical power produced with PCSS-driven laser diode arrays is presently 50 kW in 75 ps wide pulses or 12 kW in 1 ns wide pulses. A variety of sizes of GaAs PCSS are being tested around voltage and current specifications of several applications. Voltages range from 2 to 100 kV, currents range from 10 to 500 A, and electrical pulse lengths range from 1 to 50 ns. This paper discusses developmental issues of GaAs PCSS, which are common to all: fundamental research in high gain GaAs, device longevity, optical triggering, circuit configuration, and switch performance