Dynamic Fizeau interferometer using low-coherence light source

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 with /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 0.024 and 0.026 respectively.