针对现有光弹调制器标定方法的不足,提出了一种精确标定光弹调制器的新方法。首先利用起偏器、波片、光弹调制器和检偏器构成标定光路,通过寻找探测信号基频分量的极大值进行粗略标定,使光弹调制器的峰值延迟量处在1.841 rad附近。然后撤走波片形成光弹调制器的精确标定光路,在检偏器旋转90°前后获得探测信号的直流分量和二次谐波分量。最后利用这两种探测信号的直流分量和二次谐波分量精确地计算出光弹调制器的峰值延迟量。实验验证了此光弹调制器标定方法,实验结果表明其标定误差仅为0.7%。在此光弹调制器标定方法中,光弹调制器的标定精度和入射光强、电路参量无关。同时,标定要求的峰值延迟量小,非常适合于光弹调制器在其使用波长范围长波段的标定。

A new method to calibrate accurately a photoelastic modulator is proposed to compensate for the shortcomings of current calibration methods. Firstly, the photoelastic modulator is calibrated roughly to locate its peak retardation around 1.841 rad using the fundamental component's maximum of the detection signal in an optical system for calibration which is composed of polarizer, waveplate, photoelastic modulator and analyzer. Then the waveplate is taken away to form an optical system for accurate calibration. Before and after the analyzer is rotated, the direct current and secondary harmonic components of the detection signals are obtained to calculate the peak retardation of the photoelastic modulator. The accurate calibration for the photoelastic modulator is realized and its precision is independent of the incident intensity and the circuit parameters. The calibration method was verified by experiments. The calibrated error of the method is less than 0.7%. The peak retardation of the photoelastic modulator is small in the calibration, so the photoelastic modulator can be calibrated in the long-wave band of its spectral range using this calibration method.