液晶盒表面面形的质量会影响空间光调制器的性能。为了精确测量液晶盒表面面形, 提出了短相干载频干涉方法。利用短相干扩展光源进行照明, 产生的参考光和测试光之间形成定域干涉, 通过控制参考面和液晶盒表面之间的倾角, 引入合适的载频, 得到待测载频干涉条纹; 同时空液晶盒空气层上下表面干涉, 形成背景干扰条纹, 从而在CCD相机中采集到混叠有一组干扰条纹的单幅载频干涉图。通过空间傅里叶变换方法滤除背景和干扰条纹的频率信息, 提取并恢复待测条纹包含的面形数据。实验检测了两块玻璃基片错位粘合制成的液晶盒表面面形, 解算出波面峰谷值PV为8.286λ, 波面均方根值RMS为1.782λ。使用该方法和ZYGO干涉仪进行的对比实验中PV值和RMS值分别相差0023λ和0.004λ, 两种测量方法得到的结果一致。该方法能够克服多表面干涉的问题, 实现液晶盒表面面形的精确测量。

The quality of the liquid crystal cell surface can affect the performance of the spatial light modulator. In order to accurately measure the liquid crystal cell surface, a low coherent carrier frequency interference method is proposed. Illuminating with a low coherent extended light source, forming a localized interference between the reference light and the test light, and adding a suitable carrier frequency by controlling the tilt angle between the reference surface and the surface of the liquid crystal cell, the carrier frequency interference fringe to be tested is obtained. The upper and lower surfaces of the air layer of the empty liquid crystal cell form a background interference fringe, so that a single carrier frequency interference pattern with a set of interference fringes is collected in the CCD camera. The frequency information of the background and the interference fringes is filtered by the spatial Fourier transform method, and the surface data of the fringes to be tested is extracted and restored. The surface of the liquid crystal cell made by dislocation bonding of two glass substrates was tested. The peak-to-valley value PV of the surface is 8.28λ, and the root mean square value RMS is 178λ. Comparative experimental results conducted by the method and ZYGO interferometer indicate that the differences of PV and RMS are 0.02λ and 0.004λ. The results obtained by the two measurement methods are consistent. The method can overcome the problem of multi-surface interference and measure the liquid crystal cell surface precisely.