Optical methods of measuring rough surfaces

Abstract

The statistical parameters of surfaces to be measured for industrial applications vary over several orders of magnitude. Surfaces with large slopes or edges are particularly difficult to be recorded. Some measuring methods developed in our laboratory are compared and the range of applications are discussed. For polished and fine ground glass and metal surfaces a heterodyne profilometer with a vertical resolution of 0.5 nm, lateral resolution of 0.6 &#956;m, and large scanning length is discussed. The interferometer can be changed from single- to double-pass operation by rotation of a quarter-wave-plate. For rougher surfaces a profilometer of the photometric-balance type with resolution Rq < 4 nm and dynamic range of 20 &#956;m and an interference microscope with automated fringe evaluation is described. An integral white light roughness sensor covers the roughness range 0.04&#956;m to 10&#956;m and measures independently mean roughness and autocorrelation width.