采用频率梳方法测量太赫兹频率时, 其测量精度取决于重复频率的锁定精度和拍频信号的测量精度。拍频信号频率由频率计数器测量得到, 对信号的信噪比(SNR)和信号强度均有要求, 且SNR越高频率测量精度越高。因此, 拍频信号的探测和SNR的提高是太赫兹频率测量中最关键的环节。系统地研究了影响拍频信号信噪比的主要因素, 包括拍频产生方法、信号放大方案、拍频频率以及被测光源功率对拍频SNR的影响。通过全面的系统优化, 在实验上获得了SNR优于60 dB的拍频信号, 为太赫兹频率的高精度测量奠定了良好的基础。

The measurement accuracy of terahertz frequency by using the frequency comb method depends on the locking accuracy of the repetition rate and the measurement accuracy of the beat signal. The frequency of the beat signal is measured by the frequency counter, so the signal-to-noise ratio (SNR) and the power of the beat signal are required to be high enough. The higher the SNR, the higher the accuracy of the frequency measurement. Therefore, the detection of the beat signal and high SNR are very important in terahertz frequency measurement. The main factors of the SNR of the beat signal are studied systematically, including the generation method of the beat signal, the signal amplification, the beat frequency and the power of the measured terahertz source. Through comprehensive optimization, the beat signal with SNR better than 60 dB is achieved experimentally, which provides a good foundation for the high accuracy measurement of terahertz frequency.