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Phase-Shifting Interferometry for Determining Optical Surface Quality

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Phase-Shifting Interferometry for Determining Optical Surface Quality

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Determining the surface quality of a critical component, the deviation from the intended shape whether flat, spherical, etc.is crucial to high-precision manufacturing. Traditional methods consist of an interferometer, for example a Twyman-Green interferometer (pictured below) that compares the test optic to a reference. Differences in optical path length between the two arms of the interferometer lead to fringes in the photodetector typically a CCD array. Points lying on the same fringe center are at an equal optical path-length difference while points on adjacent centers represent a difference of a half wavelength. Introducing a small tilt between the reference and test optic results in an interferogram where any deviation from an evenly spaced straight fringe implies an aberration in the test component.

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