为解决远距离处人工地震波的检测问题,研究了光源的相干性,系统的稳定性,激光多普勒信号强度、信噪比,位移测量灵敏度和精度等理论及方法。采用在腔内插入两个直径为1.8 mm的可变光阑和输出光的准直结构(4倍),增大光源的相干长度和可测距离;在两路光中分别加入声光调制器和λ/4波片,实现偏振态匹配并使系统工作更稳定,提高信噪比;采用透镜聚焦接收,增大信号强度;采用特伦逆向反射装置,消除它在位移或振动过程中因偏摆或横移所带来的影响,使测量灵敏度和精度提高约一倍。将此系统用于2 m处的振动进行原理性实验,其振幅测量相对误差为0.1%,可测频率最高为750 Hz,因此可用于高空遥测人工地震波。

To measure artificial seismic wave with high accuracy in remote distance, the theory and methods of coherence of light resource, stability of system, intensity and signal to noise ratio (SNR) of laser Doppler signal, and sensitivity and accuracy of displacement measurement are investigated. Two optical stops (whose diameter is 1.8 mm) inserted into the resonant cavity and collimating structure of light output (4×) are adopted to increase coherent length and measurable distance. Acousto-optical modulation device and 1/4 wave plate are inserted respectively into two light paths to implement the matching of polarization, to make the system more stable and the SNR higher. The lens focusing is adopted to increase signal intensity. Trent reverse reflection device is adopted to offset the effect caused by beat and cross sliding during displacement or vibration and to enhance measurement sensitivity and accuracy nearly one time. Through the principle experiment of vibration in 2 m distance by using above system, the measurement relative error of amplitudeis of 0.1% and the measurable frequency up to 750 Hz are obtained. So the system can be applied to remote measurement of artificial seismic wave in high altitude.