DUAL-WAVELENGTH HETERODYNE DIFFERENTIAL INTERFEROMETER FOR HIGH-PRECISION MEASUREMENTS OF REFLECTIVE ASPHERICAL SURFACES AND STEP HEIGHTS

A dual-wavelength heterodyne differential interferometer was developed and tested together with scanning mechanics. To extend the range of u nambiguity, two wavelengths were applied. This is important for measur ing structures with surface discontinuities (reliefs, steps). The auto matic adjustment of the interferometer with respect to the rotational symmetrical measuring surfaces (aspheres) is important. An adjustment is needed to scan the asphere through its vertex. Typical measurements on a sphere, an asphere, and steps are shown. (C) 1996 Optical Societ y of America