Patent ID: 6757067
Filing Date: 2004-06-29
Classification: G01B

Abstract:
A method of measuring a transmissive plane parallel plate with a grazing incidence interferometer comprising steps of:reflecting a beam of light at a non-normal grazing angle from both a reference surface and two nominally parallel surfaces of the transmissive plate producing at least two different interference patterns; superimposing a first of the interference patterns that is formed between the reference surface and one of the two nominally parallel surfaces of the transmissive plate on a second of the interference patterns that is formed between the two nominally parallel surfaces of the transmissive plate; varying the non-normal grazing angle of the beam through a range of angles at which local fringe intensities of each of the superimposed interference patterns shift through at least one cycle; determining a modulation frequency at which the local fringe intensities shift within one of the superimposed interference patterns; and evaluating the local fringe intensities varying at the modulation frequency to extract phase information from the one interference pattern.