Use of Multilayer Films for Surface Topography Interferometry

Abstract

An experimental study is made of the suitability of multilayer reflecting films of zinc sulphide and cryolite for the examination of surface topography by multiple-beam interferometry. It is shown that the low absorptions of the films lead to fringe definition for reflection fringes, much superior to that given by silver of corresponding reflectivity. The wavelength selectivity of second-order films is made use of for viewing the surface detail through the matching flat by changing to a wavelength region wherein the multifilm is transparent. It is shown how the wavelength characteristics can rapidly be assessed with white light fringes of equal chromatic order. The good contouring properties of the multilayers are established experimentally, and there is close contouring at least down to steps of 90A in height. An application to vibrational studies is indicated. It is considered that the multilayers have considerable advantages for studying opaque surfaces.