Nanometric Surface Finish Measurement by Optical Diffraction

Abstract

The use of light scattering or diffraction for the determination of surface roughness of machined metal components has been investigated by many researchers. As a result, a number of theoretical formulations have been derived for the calculation of the scattered light intensity distribution. Based upon scalar scattering theory, formal relationships can be derived, linking: (i) the specular reflectance to the RMS height parameter Rq, and (ii) the standard deviation of the scattered light to the RMS slope parameter Δq. Based upon light-scattering techniques, various commercial surface finish sensors have been developed. Three of these instruments are discussed. Their essential difference is in the numbers of photo detectors, which leads to differences in surface finish parameter measurement capability.