A technique for the measurement of surface roughness using a non-contact optical profiler is presented for the measurement of surfaces having RA's of up to 2.5 μm (100 μn). The optical profiler uses phase-measurement interferometry to directly measure surface height profiles at a single wavelength of illumination. By utilizing information from surface height measurements made at two different wavelengths, surface profiles with peak-to-valleys of up to 20 gm (800 μn) can be determined. The technique presented is non-destructive, quick, and has an rms repeatability of better than 25 nm (1 μn). Results of measurements made with both linear and area detector arrays on calibrated roughness standards as well as on machined surfaces are presented.
James C. Wyant,
"Interferometric Measurement Of The Roughness Of Machined Parts", Proc. SPIE 0954, Optical Testing and Metrology II, (16 January 1989); doi: 10.1117/12.947596; https://doi.org/10.1117/12.947596