Grating interferometer for flatness testing.
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 microm, 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.
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de Groot