Two diffraction gratings placed in front of a f lat surface generate an interference pattern representing the surface deformations. The interference pattern is achromatic and has an equivalent wavelength between 4 and 40 µm, depending on the grating frequencies and the viewing angle. Using phase-shifting techniques, the grating interferometer provides high-precision profile measurements of both smooth and rough surfaces.
© 1996 Optical Society of America
Peter J. de Groot, "Grating interferometer for flatness testing," Opt. Lett. 21, 228-230 (1996)