Some Problems Study On The Generation Of Ultrashort Electromagnetic Pulse Using Photoconductive Semiconductor Switches

The ultrashort electromagnetic pulses have a broad applied foreground in ultra-wideband randar, ultra-wideband communication and THz imaging systems. As far as the power and band width of the electromagnetic pulses are concerned, the generation of electronic pulses by photoconductive switches is more effective. Some problems about generation ultrashort electronic pulses using SI-GaAs photoconductive switches are investigated in this paper.It is a new technology that combine the photoconductive switch with the ultra-short pulse laser to generate the ultrashort electromagnetic pulse. The base principle that generate the nanosecond^ electromagnetic pulse is changing the conductance of Semi-insulating(SI) GaAs, which the DC voltage accrose the switch ,by using the ultrashort laser pulse. The experiments of various gap switches being triggered by difference wavelength laser were performed. Based the semiconductor optoelectroniccs theory , the author discussed the GaAs material's absorption mechanism in the paper. In experiments, the phenomena were observed that the semi-insulating GaAs photoconductive switches can absorb 1064nm laser obviously, which is out of the switch absorbing range. The experiments indicate there exists non-intrinsic absorption mechanism, which is different with intrinsic absorption mechanism. The paper discussed this non-intrinsic absorption mechanism based on the theories of EL2 energy level and double-photon absorption. The experiments show the switch can also enter linear mode, nonlinear model and complex model when the switches are triggered at different electrical field and different energy irradiation. The complex model is a specificIIIphenomena proper for triggering by 1064nm laser pulse. The paper discussed the relation about EL2 energy level and these three modes. The risetime of electrical pulse and the delay-time between the linear model and nonlinear model are calculated in this paper, and the results match the experimental measure. The paper also discussed the trigger laser, structure of switch, material of switch, and the structure of electrode. The experiments of generating electromagnetic pulse by photoconductive switch were performed, and the electromagnetic pulses were emitted and received through wide-band antennal. The experiments indicated that the wide of electrical pulse is less than Ins, and its bandwidth is 6.5GHz. These experimental results reached a top level in china.