Analysis Of Terahertz Radiation Under Nonlinear Mode Of Large Aperture Photoconductive Antenna

In view of great applied foreground of terahertz (THz) radiation in the domains of biomedicine, security, imaging and communication, which made generation and detection technology of THz wave be hot all world. Photoconductive semiconductor switches 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 mode and nonlinear mode has compared.From the aspect of incident laser pulse energy and duration, the influence of antenna inner carrier density with incident light FWHM and triggering energy has analyzed. And current continuity equation is applied to analyze current variety of SI-GaAs under high electric field. Using Drude-Lorentz model, and combining incident light and far-field radiation, the relationship between the current and THz radiation has obtained. Moreover, the two factors, namely the change of carrier density and carrier acceleration, which determined the derivative of current have analyzed.The effect of incident light energy to nonlinear work mode has discussed. And the high power femtosecond laser is necessary to the nonlinear mode; when under nonlinear triggering, the effective electric field has seriously weakened by screening effect of radiation field; Moreover, the existence of long lock-on electric field limit triggering frequency for breakdown limitation, so radiation power would be limited. When the screening effect vanished, the effective electric field would comeback to biased field and formed charge domain in antenna. The frequency of radiation originate from high field in charge domain has calculated. This frequency is located in THz band. And the relative amplitude of THz radiation originating from avalanche impact ionization has calculated. The result reveals that there will be intense THz radiation from this process. Above conclusions will be useful to the design and experiment of large aperture SI-GaAs photoconductive antenna.