提出了一种基于双弹光差频调制的中红外相位延迟精确测量方法。通过两个硒化锌型弹光调制器(PEM)的差频降低系统调制频率,产生载有被测相位延迟的低频调制信号,调制后的1倍差频幅值和2倍差频幅值相除可求得被测波片的相位延迟。该方法可有效抑制光强波动及PEM相位延迟波动对测量的影响,提高测量精度。对测量原理进行了理论推导,设计了硒化锌型PEM和实验系统。实验结果表明,相位延迟测量误差不大于0.004%,灵敏度可达5×10 ^-4 rad。

A new method for precisely measuring mid-infrared waveplate phase retardation based on dual photoelastic frequency difference modulation is proposed. The modulation frequency of the waveplate measurement system is reduced by the frequency difference between two ZnSe dual-photoelastic modulators (PEMs), and low-frequency modulation signal carrying the tested retardation is generated. The phase retardation of the tested waveplate is obtained by dividing the 1-time frequency difference amplitude and 2-time frequency difference amplitude after modulation. The effect of light intensity fluctuations and PEM phase retardation fluctuations on the measurement precision of the system is effectively suppressed by the proposed method and the measurement precision is improved. The measurement principle is deduced theoretically. The ZnSe-PEMs and the experimental system are designed. The experimental results show that the relative error of phase retardation measured is better than 0.004% and the sensitivity can be up to 5×10 -4 rad.