A synchronous phase-shifting
Fizeau interferometer comprises a half-wave plate, a focusing lens, a diaphragm, a
beam splitter, a first collimating lens, and a birefringent thin-film standard lens, which are arranged sequentially along the beam advancing direction of a linearly polarized
laser source, wherein the diaphragm is positioned on the back focus and the front focus of the first collimating lens; a second collimating lens and a synchronous phase shifter are sequentially arranged in a direction perpendicular to the beam advancing direction of the
beam splitter; the beam having a surface to be detected on the linearly polarized
laser source passes through the emergent direction of the birefringent thin-film standard lens; the birefringent thin-film standard lens is a standard
flat panel and has an antireflection film on the incident surface of the standard
flat panel and a birefringent thin film and an antireflection film on the emergent surface; and the birefringent thin film has a phase
delay of 90 DEG. The synchronous phase-shifting
Fizeau interferometer has the advances of no principle return error, long measurement distance, simple structure and easy operation.