光腔衰荡法的单波长反射率测量实验研究

Experimental study of reflectivity measurement of single wavelength by cavity ring-down method

分析了反射率光腔衰荡法测量原理的近似条件,讨论了共焦腔的失调特性,计算了腔镜反射率对衰荡信号的影响。在此基础上,为减少OPO激光束的衍射损耗引入的测量误差,选择He-Ne激光作导引光,建立以共焦腔为衰荡腔的单波长反射率测量装置。利用直腔和折叠腔对腔镜和插入镜片的反射率进行了实验测量。直腔方式下测量的均方差小于6×10-6。分析表明,光腔衰荡法只适用于高反镜反射率的测量;在光路调节中采用具有对数变换功能的示波器,可以提高测量精度。

Approximate condition of reflectivity measurement with cavity ring-down method is analyzed, misadjustment characteristic of confocal cavity is discussed and influence of cavity mirror＇s reflectivity on ring-down signal is calculated. In order to lessen metrical precision from diffraction losses of OPO laser, based on the above analyses， a reflectivity measuring system for single wavelength is set up with cavity ring-down method,whose ring-down cavity is confocal cavity. Experimental measurement of reflectivity of cavity mirror and inserted mirror is carried out. The measurement RMS in linear cavity is less than 6×10^-6， Results show that cavity ring-down method is only for higher reflectivity, and metrical precision can be improved by using logarithm transform of oscillograph in adjustment of the optical cavity。