2002 年 68 巻 7 号 p. 958-961
This paper deals with a new measuring method of specular reflectance of a plane surface using a single slit. Illuminating light and its light reflected at the surface are incident on the slit simultaneously. A ratio of second to first peak intensity of the diffraction pattern formed by the slit is proportional to the reflectance of the plane surface. An angle of incidence is variable from 80°up to 89°with the slit of width 100μm. It is possible to measure a small surface of 18 mm 2 at 89°. The measurements of reflectance are carried out with some specimens using a linearly polarized light. The measured reflectance R s and R p of Optical flat(Quartz, flatness λ/10, nd=1.4538) agree well with those of calculated by Fresnel's formulae. This method is applicable to the measurement of the surface roughness and the glossiness of low reflectivity.