半绝缘GaAs光电导天线辐射THz电磁波展宽特性分析

An Analysis of the Broader Characteristic of Terahertz Wave Radiation from SI-GaAs Photoconductive Antennas

介绍了自洽式多粒子蒙特卡罗方法模拟半绝缘GaAs光电导天线辐射THz电磁时域波形。模型中采用光能、脉宽可调飞秒激光器作为触发光源,模拟的THz电磁波形与实验基本吻合。通过载流子在光电导体内的动态输运特性,分析了辐射THz电磁波场比触发光脉冲展宽的物理机制在于:光生载流子在外电场作用下,从初始状态到速度达到稳态要经历一个动量和能量弛豫过程,而正是由于载流子动量和能量的弛豫过程导致光电导天线辐射的太赫兹波展宽。高光能、低偏置电场下,空间电荷电场是造成光电导天线辐射的THz波呈现双极性的主要原因。

This paper introduces a self-consistent multi-particle Monte Carlo approach for simulating the time-resolved terahertz radiation from SI-GaAs photoconductive antenna. Optical pulse energy and width adjustable femtosecond laser in the model are adopted as the triggering light resources. The simulated THz electromagnetic waveform is found to be basically identical with that obtained from the experiments. Through the dynamic transporting characteristics of carriers within the photoconductor, the radiation THz pulse width is analyzed in comparison with the width of pump pulse, whose physical mechanism lies in： in the biased electrical field, the photogenerated carriers from initial state to the speed reaching the stable state must experience the momentum and energy relaxation. It is just the process of carrier momentum and energy relaxation that leads to the widening of THz wave radiation by photoconductive antenna. In the case of high energy optical and the low biased electric field, the space electric charge field is the main reason to cause the THz waves of photoconductive antenna to appear the bipolar.