Abstract

In the last few years one can observe a renaissance of partially coherent illumination in interferometers. The reason behind is the roughening of wavefronts due to dust diffraction, inhomogeneities, and the remaining micro-roughness of all optical components within the light path. Illumination with the TEM₀₀ mode of a laser will show these effects in the interference pattern rather clearly /1/. Because of the heterodyne advantage of interferometry small scattered light amplitudes result in rather pronounced modulations of the lateral intensity distribution of the laser beam and inevitably give rise to small lateral phase modulations on the order of 1/100 of a light wave. These small phase variations can easily be detected in a laser interferogram even if the light has carefully been filtered with the help of a pinhole in the collimation optics. The amount of phase uncertainty introduced in the measurement of surface shapes and other parameters of optical components depends on the type of interferometer as well as the amount of tilt fringes in the interferogram.

© 1998 Optical Society of America