A new pattern projection method for wide range of surface roughness measurement

A new surface roughness measurement using pattern projection method is proposed. The current method, which the author called the OTF method, uses one imaging system including the surface to be measured as a part of the system. The range of measurement with this method has been restricted to surface roughnesses smaller than about 1/10 of the optical wavelength used. The proposed method can expand the range into that larger than the wavelength, which is important for practical use, by using the re-imaging method named by the author. This system consists of two imaging systems in which the light source in the first imaging system projects an optical pattern on the surface to be measured, and the second imaging system forms the output image of the pattern on the observing plane. The output image is the resultant image composed of the image formed by the two-step imaging system directly and that originated from the scattering on the surface. The deformation of the resultant image depends on the smoothness of the surface, and hence the surface roughness is detected from the degree of the deformation. The ability of the measurement of the surface roughness with this method is explained in this paper.