Surface roughness evaluation by laser speckle

This study describes the novel evaluation method of surface roughness by laser speckle. We observed the reflectance speckle patterns of seven sample metal plates that have different surface roughness. Thereafter, by using computed correlation functions from these patterns that includes information of surface form. By counting the peak on the line profile in horizontal direction of the correlation function, we tried the quantification of surface roughness. On the other hand, we measured surface roughness of the samples by the contact stylus instrument. Five parameters, such as Ra, Ry, Rz, Pc, and Sm were measured. We compared the peak number of correlation function with JIS parameters. As the result, it became clear that the peak number is in proportion to JIS parameter. In a word, JIS parameters could be measured based on the peak number of correlation functions. This evaluation method by laser speckle could give the surface roughness of a sample rapidly in non-destructive and non-contact. It takes about 3 seconds to get the surface roughness of a sample.