Achromatic phase shifting for polarization interferometry

Abstract

Polarization interferometers are widely used in microscopy. In these interferometers, the two beams traversealmost identical paths, so that conventional phase-shifting techniques cannot be used. However, because thetwo beams leaving a polarization interferometer are orthogonally polarized, it is possible to use a phase shifteroperating on the geometric phase to introduce a variable phase shift between the two beams without any changein the optical path difference. Since this phase shift is very nearly independent of the wavelength, small variationsof the optical path difference over the field can be mapped accurately, even with white light. Achromatic phaseshiftingcan also be used with two-wavelength illumination to provide a quick and simple method for profilingsurfaces exhibiting steps with heights of a few micrometres.