Multiple-Beam Fringes of Equal Chromatic Order Part VI Method of Measuring Roughness*

Abstract

A new method of measuring the roughness of a polished glass surface is reported. Fringes of various orders, n, are formed at the same wavelength. The measured half-width is plotted as a function of 2/n. The slope S of the best straight line through the experimental points is used to obtain a roughness value from an independently determined, experimental function S vs h(rms). The term h(rms) is the root-mean-square height of the irregularities on the equivalent surface. When this experimental function is extrapolated to h(rms)=0 the corresponding value of S is compatible with a value estimated from theory for the case of super-smooth surfaces.