May 22, 2019

Laser-driven semiconductor switch for generating nanosecond pulses from a megawatt gyrotron

Picard, Julian F., Samuel C. Schaub, Guy Rosenzweig, Jacob C. Stephens, Michael A. Shapiro, and Richard J. Temkin. “Laser-Driven Semiconductor Switch for Generating Nanosecond Pulses from a Megawatt Gyrotron.” Applied Physics Letters 114, no. 16 (April 22, 2019): 164102. 

A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 ls, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Under the same conditions, a single GaAs wafer yielded 24 ns 110 GHz RF pulses with >78% reflectance. For both semiconductor materials, a higher value of reflectance was observed with increasing 110 GHz beam intensity. Using two active wafers, pulses of variable length down to 3 ns duration were created. The switch was tested at incident 110 GHz RF power levels up to 600 kW. A 1-D model is presented that agrees well with the experimentally observed temporal pulse shapes obtained with a single Si wafer. The LDSS has many potential uses in high power millimeter-wave research, including testing of high-gradient accelerator structures.