Low-coherence phase-shifting shearing interferometer for measuring parallelism of parallel surfaces of transparent samples

A novel low-coherence phase-shifting shearing interferometer for measuring parallelism of parallel surfaces of transparent samples was proposed in this research; wherein the shear devices are two identical Savart prisms, the first one laterally separates the incident beam into two linearly polarized beams vibrating perpendicularly, and the second recombines the separated beams after they pass through the sample being examined; the phase-shifter is an assembly of the second Savart prism and a rotation stage; and the measurements are done by two operations: derivative determination and Frankot–Chellappa reconstruction. This paper sequentially introduces the configuration, measurement theory, and experimental setup of the interferometer; it then presents and discusses the results from the uses of the experiment setup. The results not only verify the validity and feasibility of the interferometer but also exhibit a maximum standard deviation of repeated measurements of 0.018 μm.