衰荡腔测量中的腔参数选择

 基于谐振腔失调灵敏度参量随腔长的变化关系，提出了一种衰荡腔，它是由共焦腔将腔长缩短为原来的0.73得到的稳定腔。根据光束传输规律和失调腔矩阵方法，以及光腔衰荡法测量原理和曲线拟合方法，建立了腔长、腔镜角度失调下光腔衰荡法的反射率测量模型。通过数值模拟，研究了这种稳定衰荡腔中，腔微小失调对反射率测量结果的影响，并与相同失调情况下共焦衰荡腔的测量结果进行了对比分析。结果表明，这种稳定腔用作衰荡腔，测量结果受腔镜角度失调影响较大，而受腔长失调影响小；其长度较短，便于工程应用；衍射损耗较小，测量精度高。

Choosing cavity parameters in cavity ring-down method

Based on the change of misalignment sensitivity with the length of cavity, a kind of ring-down cavity is put forward, which is stable resonator, and its cavity length is 0.73 times as that of confocal cavity. According to propagation equation of Gaussian beam and matrix of misadjust resonator, as well as principle of cavity ring-down method and data processing of fitting, a physical model of reflectivity measuring is set up for misadjustment of cavity length or angle of titled cavity mirrors. Applying this model, the influence of minute cavity misadjustment on measured reflectivity of cavity mirrors in the stable resonator is analyzed, which is compared to that in confocal resonator. Used as ring-down cavity, this stable resonator has, firstly, more influence of misalignment of cavity mirrors on its measured reflectivity, but less of length misadjustment; secondly, shorter cavity length which advantageous in engineering; finally, less diffraction loss and thus higher metrical precision.