Study On The Characteristics Of Sub-nanosecond Electric Pulses Generated By Gaas Photoconductive Switches

High-power ultra-fast electrical pulses(nanoseconds,sub-nanoseconds,picoseconds)play a major role in high-tech fields such as ultra-wideband radar,biomedical,terahertz technology,weapon ignition,and inertial confinement fusion.The core technology for generating high-power ultra-fast electrical pulses is switching technology.Compared with other switches,photoconductive switches have an irreplaceable advantage in generating nanosecond,sub-nanosecond,picosecond ultrafast electrical pulses.In this thesis,the ultra-fast characteristics of the output pulse of GaAs Photoconductive Semiconductor Switch(GaAs PCSS)in linear mode are studied.The experimental law and mechanism of the rising edge time of GaAs PCSS output ultra-fast electric pulse are analyzed.Based on this,this paper mainly carried out the following work:(1)A planar microstrip line with a characteristic impedance of 50Ω is designed.The high-frequency structure simulation software HFSS is used to simulate the electromagnetic structure of the SMA connector to the microstrip line.The results show that when the bandwidth of the transmitted electrical pulse signal in the transit structure is 0～20GHz,the transmission power loss of the signal in this structure is very small,and the power transmission efficiency is above 92%.(2)Using a picosecond,femtosecond laser to trigger a semi-insulating GaAs PCSS with an electrode gap of 1.5 mm and 3.0 mm,and analyze the triggering of light energy,electrode gap and storage capacitor under linear conditions,and the rising edge time of the output ultrafast electrical pulse.Experimental rules and mechanisms.The experiment found that as the triggering light energy increases,the rising edge time of the output electric pulse gradually becomes slower;the larger the storage capacitor,the slower the discharge speed of the capacitor in the same time,and the photoconductive switch responds to the optical pulse slower,thus The rising edge time is slower.(3)When the bias voltage is 900V and the trigger energy is 9.28μJ,a semi-insulating GaAs PCSS with an electrode gap of 1.5mm is triggered by a femtosecond laser with a wavelength of 800nm and a pulse width of 100fs,and an ultra-fast current with a rising edge time of 53ps is obtained.pulse.The experimental result is that GaAs PCSS is currently able to produce the fastest ultra-fast electrical pulse with the fastest rise time.(4)The possible factors of GaAs PCSS output ultra-fast electric pulse are discussed:material characteristics of photoconductive switch(carrier lifetime and average drift speed),trigger light pulse(pulse width,wavelength and trigger mode,etc.),experimental circuit Parameters(photoconductive switch parasitic inductance and parasitic capacitance and microstrip transmission system,etc.),among which photoconductive switch material characteristics are the most important factor in the output limit ultra-fast electrical pulse.