数据拟合点的截取对光腔衰荡法测量反射率的影响

Influence of fitting data number on measurement of reflection based on cavity ring-down

利用光腔衰荡法测量反射率,探测器性能对衰荡信号的测量有很大影响,具有不同时间响应和灵敏度特性的探测器会得到不同的信号衰荡曲线起始点和信号淹没点。对于性能相同的探测器,在测量反射率不同的反射镜时,也会得到不同的信号淹没点。在数据拟合过程中,截取不同的数据起始点和信号淹没点,会得到不同的衰荡时间,从而影响反射率的测量精度。对衰荡信号进行对数变换,首次利用χ2拟合对数据进行处理,通过对有效拟合数据与斜率误差关系的分析,得到了最佳拟合数据点截取的方法。实验证明:此方法可有效处理无效光信号和噪声信号的分界点,给出了衰减时间的数据截取依据,有助于改善时间衰荡法测试的精度和重复性。

In measurement of reflection with cavity ring-down ,the detector＇s capability has a great influence on the measured figure of ring-down signal. For the different responsibility and sensitivity, the different starting and ending points will be obtained. For the same detector, the different ending point will be obtained during measuring the reflectors with different reflection. The starting and ending points influence the fitting results greatly. Logarithm function was used to transfer the ring-down signal, and then chi-square fitting method was used to process data. The uncertainty of the signal slope was analyzed. Based on the relationship of fitting data number and the slope error, the appropriate interception method of fitting data was obtained, which reduced the influence of noise to the least degree. Experiment shows that this method can be used effectively to obtain the boundaries of the invalid optical signal and the noise signal, estimate the truncation of ring-down signal data and improve the accuracy and repeatability of the ring-down time testing.