A large-aperture Phase-Shifting interferometer created for measuring the characteristics of optical elements with flat surfaces. The peculiarity of the interferometer is that as a result of the calibration of its reference plates an absolute measurements accuracy of ~λ/1000 (RMS) has been attained over the entire field of view.

A Large-aperture Phase-Shifting interferometer is constructed according to the Fizeau interferometer scheme (Fig.1). The field of view of the interferometer is 630 mm in diameter. The length of the interferometer is ~4.2 m. The interferometer is mounted on a table with pneumatic supports to reduce vibrations (Fig.2). Interferometer main feature is to achieve an absolute measurement accuracy of ~λ/1000 (RMS) over the entire field of view.

One of the key parts of the interferometer is its software. It is intended for recording the initial data on the intensities of interference patterns, their subsequent processing, and the presentation of experimental results in a form suitable for their use. Due to the interferogram phase shifting by tuning the probing-radiation wavelength, this interferometer is also capable of measuring the optical thickness and surface profiles of plane-parallel plates.