Research On Non-linear Gaas Photoconductive Semiconductor Antennas By Low Light Of Nano Joule Magnitude

With the development of THz technology,it can be widely used in radar,remote sensing,homeland security and counter-terrorism,atmospheric and environmental,medical diagnosis,real-time biological information extraction,and secrecy communication and transmissions,which made generation and detection technology of THz wave be hot all world.Photoconductive semiconductor antennas(PCAs)act as source of power pulse and wideband electromagnetic radiation,so it could be used to radiate THz wave with virtue of compact and easy-fabricate.This paper firstly gives a summary to the THz technology and its application.Based on the theory of optically activated charge domain,the generation mechanism of nonlinear work mode of photoconductive antenna has explained.And the difference between the linear and nonlinear mode has compared.Making an conclusion of the advantage of getting THz wave from non-linear mode and the reason that THz wave cannot be produced from PCA working in non-linear mode.The reasons are the low energy of triggering light source in THz-TDS and the "lock-on" phenomenon which influences the lifetime of PCA in non-linear mode.Based on the relation of THz radiation,carriers in PCA and bias voltage,explaining large-aperture PCA,working in non-linear mode,can produce THz wave.The threshold of optical energy which made PCA working in non-linear mode is calculated in theory,and its numerical value is 1.1 nJ.The calculating result demonstrate that the luminous energy of fs lasers which are used in THz-TDS system can satisfy the demand of PCA working in non-linear mode.Setting up and optimizing the system of triggering,utilizing oscilloscope(OSC)monitor woring mode of PCA.Because of the measure result of nano-joule order energy used to trigger PCA can be influenced easily by other optical,we devise real-time optical system to enhance measure accuracy.Analysis the absorption mechanism of GaAs material and test the absorption rate of GaAs chip under different energy and wave length for the setting up of experiment system and analysis of the result.Based on low optical energy triggering system,a 0.55 mm-gap GaAs PCA operated on non-linear mode with the bias electrical field of only 78 kV/cm and the trigger energy of as low as 24.3 nJ.This result solves one of difficulties which PCA produce THz wave in non-linear mode.We come up with a new concept of multiplication rate as the measurement to characterize the level of PCA working in non-linear mode.Those works and result have very important significance for generated high-power terahertz waves with photoconductive antenna operating on non-linear mode.In addition,it is very important to realize multiple PCSSs simultaneously operating on non-linear mode when the trigger laser energy is very low.