Laser heterodyne apparatus for roughness measurements of polished surfaces

A laser heterodyne apparatus for roughness measurements of polished surfaces has been developed. A new principle for generation of the local-oscillator light beam is introduced. Important features of the apparatus are: very high sensitivity (R(a) values less than 0.1 nm can readily be measured), immunity against stray light of all kinds, noncritical aligning (insensitive to vibrations), simple configuration, microprocessor output unit for digital presentation of characteristic surface measures. A quantitative theory of the complete apparatus is presented together with experimental confirmation by comparisons with stylus and multiple interference measurements.