泵浦激光频率漂移对光声稳频信号的影响

在CO2激光泵浦的气体太赫兹源中,泵浦激光的频率稳定性控制问题十分关键。针对基于光声效应的泵浦源稳频技术,理论分析和数值模拟了光声信号的探测条件(光声腔内气压、传声器灵敏度等)对微弱光声信号检测的影响,进而对探测条件进行了优化。在此基础上,进一步分析了泵浦激光频率在气体吸收谱线中心频率附近漂移时光声信号的变化规律。结果表明:在实际工作中,为了实现高精度的稳频,需要将光声腔的气压控制在低压范围内,并采用高灵敏度的光声传感器;当泵浦激光频率产生漂移时,利用探测到的微弱光声信号通过反馈系统可以精确地改变激光器的腔长,以实现高精度的光声稳频,且频率漂移范围可控制在MHz量级以内。

Influence of frequency shift of pump laser on photoacoustic signal for frequency stabilization

The frequency stability of CO2 pumping laser is of great importance for optically pumped terahertz(THz) gas laser. Aimed at frequency stabilization technique based on photoacoustic effect, the influence of detective conditions on the detection of weak photoacoustic signal in photoacoustic cell was theoretically analyzed and numerically simulated and the detective conditions were further optimized for high-precision detection of photoacoustic signal, including the pressure of methanol gas and the microphone sensitivity. On the basis, the variation of photoacoustic signal with the frequency shift of the pump laser from the center of the absorption line was analyzed. The results show that the low pressure condition and highly sensitive microphone are the keys for achieving high-precision photoacoustic frequency stabilization. When the laser frequency of CO2 pumping laser shifts from the center of the absorption line, the cavity length can be adjusted accurately by the regulation of feedback photoacoustic signal to ensure the frequency stability of output laser, and the frequency shift could be controlled within the magnitude of megahertz.