Measurement of surface roughness by means of speckle technique has the advantage of being noncontacting and applicable to an in-process environment. Results from measurements of speckle contrast on ground surfaces are shown. The measurement range in the configuration used is Rq ≤ 200 nm. Comparisons of results between calculated and experimentally achieved speckle contrast are in agreement. An empirical method is presented that can be used to classify machined surfaces according to roughness when no specular component exists in the scattered light. The measurement range of this method is highly dependent on the machining process used. Surfaces with Ra ≤ 3.2 μm are classified according to roughness.
Ulf A. Persson,
"Roughness measurement of machined surfaces by means of the speckle technique in the visible and infrared regions," Optical Engineering 32(12), (1 December 1993). https://doi.org/10.1117/12.151303