利用空气来探测脉冲太赫兹波

曾有报道利用飞秒激光脉冲通过空气中的三阶光学非线性过程产生高强度的太赫兹波．理论上，作为太赫兹波产生的逆过程，有可能实现用空气作为介质探测脉冲太赫兹波．作者以空气或激光诱导的空气等离子体作为介质，通过测量太赫兹波场诱导产生的二次谐波信号，首次实现了宽带太赫兹波的时间分辨探测，本文介绍了空气中太赫兹波的非相干和相干探测的实验结果和理论分析．迄今为止，这种具有突破意义的太赫兹波空气电离相干探测法（THz-ABCD）的频谱宽度可以超过8THz，实现动态范围可达30dB。

Sensing pulsed THz waves with ambient air

Using air with femtosecond laser beams to generate pulsed THz waves through third-order nonlinear optical processes has already been demonstrated. As its reciprocal process, in theory, it should be possible to use air as the sensor to detect pulsed THz waves. We report the first demonstration of time-resolved detection of broadband THz waves by measuring the THz field-induced second-harmonic signal in ambient air and/or ionized air (laser-induced air plasma). Experimental results and a theoretical analysis of incoherent and coherent detection are presented. A spectroscopic bandwidth of over 8 THz was observed for the air-breakdown coherent-detection system. The highest dynamic range demonstrated with an air sensor was 30 dB.