INTERFERENCE MEASUREMENT METHOD AND INTERFERENCE MEASUREMENT INSTRUMENT EMPLOYING IT

摘要

An interference measurement instrument, which acquires a high contrast interference fringe by using as measurement light a wavelength light containing little reflection light from an optical thin film when interference measurement is performed through an optical window on which the optical thin film is deposited, comprises an illuminator outputting light having wideband wavelength distribution characteristics, a wavelength filter selecting means for selecting and outputting light of at least one wavelength by receiving light from the illuminator and switching between a plurality of wavelength filters having different central wavelengths, and a half mirror for branching the wave length light selected by the wavelength filter selecting means into reference light and illumination light directed toward a measurement object and outputting interference light of the illumination light reflected from the measurement object and the reference light, wherein the wavelength filter selecting means is arranged to select such a combination of wavelength filters that allows the contrast of an interference fringe in the interference light from the half mirror to exceed a predetermined threshold or be maximized.