Spark gap triggering with photoconductive switches
Photoconductive switches are well suited for triggering spark gaps since the triggering event is short and requires very little energy. Photoswitches offer fast-rising pulses of short duration with voltage levels of several tens of kV and tens of ps jitter and can be very simple in design, whereas typical trigger sources require multiple stages to generate tens of kV needed to effectively trigger a spark gap of the same potential and usually suffer from slow risetimes. This paper presents methods aimed at triggering spark gaps with photoswitches. Both linear and nonlinear photoswitches are discussed and their associated problems are presented.
Pulse Compression Characteristics of an Opposed-Electrode Nonlinear GaAs Photoconductive Semiconductor Switch at 2 μJ Excitation
The investigation of nonlinear transient characteristics of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) is of great significance for its applications in pulsed power technology. In this letter, the laser diode (LD) energy of $2~\mu \text{J}$ is employed to trigger the opposed-electrode GaAs PCSS. The compressed pulse width and increased amplitude are obtained as the bias electric field increases from 6kV/cm to 34kV/cm. It is numerically modeled the transient electric field distribution along the photogenerated carriers’ transport. Results reveal that pulse compression effect (PCE) can be attributed to the negative differential mobility (NDM) and electric-field screening (EFS) effect. The compression of pulse width on time scale provides a possibility to relieve the heat accumulation on time scale, and further to suppress the device failure for the potential high-repetition-rate applications.
High gain GaAs photoconductive semiconductor switches for ground penetrating radar
The ability of high gain GaAs photoconductive semiconductor switches (PCSS) to deliver high peak power, fast risetime pulses when triggered with small laser diode arrays makes them suitable for their use in radars that rely on fast impulses. This type of direct time domain radar is uniquely suited for observation of large structures underground because it can operate at low frequencies and at high average power. This paper summarizes the state-of-the-art in high gain GaAs switches and discusses their use in a radar transmitter. The authors also present a summary of an analysis of the effectiveness of different pulser geometries that result in transmitted pulses with varying frequency content. To this end, they developed a simple model that includes transmit and receive antenna response, attenuation and dispersion of the electromagnetic impulses by the soil and target cross-sections.