Roughness characterization of smooth machined surfaces by light scattering.

Characterization of surface roughness has generally been limited to rms deviation from the mean and occasionally the autocorrelation length. By considering the surface to be a superposition of many sinusoidal gratings, the surface spectral density function (SDF) has been calculated from measurements of the light scattered out of a reflected He-Ne laser beam. By rotating the sample, the SDF can be found for anisotropic surfaces (such as machined surfaces). The SDF allows examination of roughness as a function of spatial frequency, which is important for many applications. Interferometric and scattering results are compared for a rough (350-Arms) machined surface, and finally a smooth (50-Arms) diamond machined surface is characterized.