不同中心波长飞秒脉冲激发InAs表面辐射太赫兹波的机理研究

The characteristics of terahertz radiation from InAs irradiated with femtosecond optical pulses of different wavelengths

研究了p型(100)InAs在不同中心波长飞秒激发光(750—850nm)作用下的太赫兹(THz)波辐射特性.这种太赫兹辐射的光谱性质与光学Dember效应密切相关,飞秒脉冲激发下产生的载流子在InAs表面的Dember场内做加速运动,从而辐射出THz电磁波.实验结果表明:不同中心波长的激发光作用下,InAs表面产生的Dember电场、光生载流子浓度、谷间散射效应以及处于不同状态的载流子数目都发生了变化,因而激发出太赫兹波的功率、振幅、频谱分布和有效谱宽是不同的.这项研究将有利于THz时域光谱技术以及实验系统的优化,对InAs表面辐射太赫兹电磁波的超快过程及其物理机理也作了进一步的解释.

The characteristics of terahertz （THz） radiation from the surface of an （100） p-InAs crystal excited by fs laser pulses of different wavelengths （from 750 to 850 nm） are investigated experimentally. The terahertz radiation can be interpreted as being emited from accelerated photo-carriers in the Dember field and be detected by using the free-space electro-optic sampling method. A （110） ZnTe crystal was used as detector. The results of experiment show that the Dember field in the surface of InAs, concentration of excited carriers, intervalley scattering and the concentration of excited carriers of different states, all changed when the wavelength of excited pulse changed, so the radiant efficiency and the effective spectral width of terahertz wave were different. This investigation will be useful to the measure of time domain spectrum of samples and the optimization of experimental system. It also gives better physieal insight into the ultra-fast process of terahertz wave radiation from InAs excited by femtosecond pulses.