OBLIQUE-INCIDENCE INTERFEROMETER EQUIPMENT

PURPOSE: To make the contrast of interference fringes sharp by providing a light quantity attenuating means in an optical path of a reference light separated from the optical path of reflection from an object of inspection between first and second diffraction gratings so that the means can be inserted into and withdrawn from that optical path. CONSTITUTION: A light quantity attenuating plate 20 is disposed between a first diffraction grating 7 and a second diffraction grating 10 and it is made displaceable in a sliding manner between a position where it faces an optical path of a reference light and a position where it is withdrawn therefrom. On the occasion when a laser light from a laser light source 1 passes through the grating 7, diffraction of the light occurs and it is separated into a zero-order light and a plus first order diffracted light on the output side of the grating 7. While the zero-order light advances straight as the reference light, the plus first-order diffracted light is reflected by an object 9 of inspection and an object light is generated. The quantity of the object light changes in accordance with the reflectance of the object 9 of inspection, and when the reflectance of the object 9 is high, the attenuating plate 20 is withdrawn. In the case when the object 9 of low reflectance is measured, the attenuating plate 20 is made to face the optical path of the reference light and thereby the quantity of the reference light is attenuated so that the difference in the quantity of light from the object light be lessened.