Roughness measurement using a shearing interference microscope

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Abstract
A shearing interference microscope has high image stability even under vibration. This paper proposes a method of rms roughness measurement of smooth surfaces using shearing interference microscope images which include interference fringes. It makes use of the fact that, when the shearing length is extended in comparison with the autocorrelation length of the rough surface, the shearing interference image has a close relationship with the rms roughness of the measured surface. Principle and theory are discussed as well as the result of measurements of precision-finish surfaces 20–100-Å rms.