采用短相干光源的动态斐索干涉仪

Dynamic Fizeau interferometer using low-coherence light source

为了实现斐索型干涉仪的动态干涉测试,研究了一种采用短相干光源的动态斐索干涉仪。以中心波长为638 nm、带宽为0.1 nm的二极管泵浦固体激光器作为光源,与偏振延迟装置结合得到一对短相干正交线偏振光,通过调节光源模块中两支线偏振光的光程差来匹配斐索干涉腔的长度,从而获取一对光程差为0的相干光束。使用偏振相机采集得到四幅位相依次相差π/2的移相干涉图,按照四步移相算法解算相位,恢复待测元件的表面面形。采用光强归一化算法有效地抑制了偏振态误差导致的移相干涉图光强不一致在最终恢复波面中引入的一倍频波纹误差。采用琼斯矢量和琼斯矩阵分析了干涉图对比度与s光和p光光强比值的关系,并分析了1/4波片方位角误差对最终恢复波面的影响。利用该装置和Zygo GPI XP型干涉仪测量了同一块光学平晶,其均方根值相差0.024λ,峰谷值相差0.026λ。

In order to realize dynamic interference measurement of Fizeau interferometer,a dynamic Fizeau interferometer using low-coherence light source was proposed.A diode-pumped solid-state laser with a central wavelength of 638 nm and a bandwidth of 0.1 nm as the light source was used to produce a pair of orthogonal linearly polarization lights with low-coherence,combined with a polarization delay device.Then a pair of coherent beams with zero optical path difference(OPD)were acquired through adjusting OPD of the linearly polarization lights to match cavity length of Fizeau interferometer.Four interferograms withπ/2 phase shift in a phase-shifting sequence were obtained by a pixelated polarizer-based camera,by using the 4-bucket algorithm,the surface shape of optical elements was derived.An optical intensity normalization algorithm was adopted to suppress the phase error,which was caused by the intensity inconsistency due to polarization error,and had the same spatial frequency as the fringes.The relationship between interferogram contrast and ratio of s-polarized light and p-polarized light was deduced through Jones vector and Jones matrix.Besides,the effect of azimuth error of the quarter wave plate on the final recovery wave surface was analyzed.An optical flat was measured by this interferometer and Zygo GPI XP interferometer,the difference of root-mean-square and peak-to-valley were 0.024λand 0.026λrespectively.