Patent ID: 6847458
Filing Date: 2005-01-25
Classification: G01B

Abstract:
1. A method for measuring the thickness variation and shape of polished opaque plates including the steps of: placing a polished opaque plate in a cavity formed between reference flats in two opposing interferometer channels to map the opposite surfaces of the plate; synchronizing the phase shifting of the interferograms in the two interferometer channels by supplying the light from a single wavelength tunable laser light source, the output beam of which is split by a beam splitter to propagate to both interferometer channels; measuring the cavity characteristics of the reference flats forming the cavity providing an oversized field of view of the opaque plate in the cavity for measuring the cavity tilt of the reference flats; determining the thickness variations of the plate from the surface mapping of the opposite surfaces of the plate and the cavity characteristic measurements; and blocking the recording of spurious light from one interferometer channel in the opposing interferometer channel.