在高反射率的精确测量中，光腔衰荡系统的腔失调直接影响着反射率测量结果的精度。根据光束传输变换规律和信号叠加方式，利用最小二乘法进行数据拟合，建立了腔失调对衰荡波形的影响模型。通过数值运算，模拟了不同腔长失调或腔镜倾斜下衰荡信号波形的变化情况。通过比较，与实验结果吻合较好。仿真结果表明，将示波器上的衰荡波形用于衰荡腔的精密调节中，可以提高测量精度。分析给出了衰荡光腔实验调节的两个判据:1) 根据衰荡波形的峰值包络线的变化趋势来调节衰荡腔的腔长;2) 根据衰荡波形中相邻奇、偶次脉冲幅值的大小对比调节衰荡光腔的腔镜角度。

During precise measurement of high reflectivity, cavity misalignment has great influence on reflectivity measurement results of ring-down spectroscopy. According to propagation equation of Gaussian beam and overlap-add of signal, a theory model is set up to research the influence of detector on its ring-down waveform by using data fitting of method of least squares. Applying this model, it is simulated on the computer that ring-down waveform changes with various cavity length maladjustments or mirror′s tilt, and the analyses is in good agreement with the experimental results. Results show, in order to improve metrical precision, it is suggested that ring-down signal on the oscillograph should be applied to adjust ring-down cavity. From the results, two kinds of criteria for cavity adjustment methods are proposed. One is that total figure of ring-down waveform should be applied to adjust cavity length maladjustments, the other is that mutuality of adjacent pulse should be applied to adjust cavity mirror' tilt.