Patent ID: 6710883
Filing Date: 2004-03-23
Classification: G01B

Abstract:
An apparatus for measuring a flatness of a thin plate, said apparatus having an optical probe comprising:a polarization beam splitter separating a laser beam emitted from a laser generator and transmitting through an isolator into a measurement light and a reference light, irradiating the measurement light to a measurement surface of a thin plate and irradiating the reference light to a reference surface arranged perpendicular to said measurement surface; a quarter wavelength plate arranged between said polarization beam splitter and said measurement surface and through which said measurement light transmits; a quarter wavelength plate arranged between said polarization beam splitter and said reference surface and through which said reference light transmits; a focusing and reflected means for focusing and reflected the measurement light reflected by said measurement surface and reflecting by said polarization beam splitter, and the reference light reflecting by said reference surface and transmitting through said polarization beam splitter; a half mirror reflecting said measurement light and the reference light which return from said polarization beam splitter; and a light receiving portion receiving said measurement light and the reference light which are reflected by the half mirror so as to interfere, converting an interference light intensity change into an electric signal, and counting the electric signal so as to measure a flatness of the measurement surface.