Characterization of engineering surfaces by infrared scattering

In industry, mechanical stylus profilometry is the prevailing technique for assessing surface roughness and related parameters of engineering surfaces. Though it is a conceptually direct method, it suffers from several drawbacks: the measurement is not area-covering, while many important features of engineering surfaces are related to three-dimensional topography; the technique is slow; and it involves physical contact with the surface under test, with the danger of damaging it. We have used infrared scattering at 10.6-mu m wavelength to provide area-covering, noncontact surface characterization of engineering surfaces. The surface power spectral density is calculated from the scattering distribution by Rayleigh-Rice vector perturbation theory. Measurements of power spectral density functions and bandwidth-limited surface roughness are demonstrated for ground and polished surfaces in the root-mean-square roughness range of 0.06 to 1.7 mu m. Good correlation with contact stylus measurements is achieved for ground and lapped surfaces. Measurement of scratch and lay characteristics is also demonstrated. (C) 1997 Society of Photo-Optical Instrumentation Engineers.