Thin-Film Interferometric Techniques for High-Magnification Topographical Studies

Abstract

THIS communication describes a simple interferometric technique for examination of surface topography without the use of optical flats, the particular advantage being the possibility of using high magnification in extension across the surface without the use of a complex interference microscope. The techniques are based upon the production of a thin transparent film of Canada balsam on the surface. A drop of Canada balsam dissolved in benzine is placed on the surface and, after spreading, dries as a thin film. The spreading is assisted by a touch of cedar wood oil. The thin film appears to follow closely the contour of the lower surface, while taking on a reasonably flat upper surface, although wrinkling can at times be detected. Illumination with monochromatic light leads to the production of an interference picture which exhibits some degree of multiple-beam interference and, as the film is very thin, high resolution, using up to 3-mm. dry objectives, can be used. Thus it is possible to examine interferometrically with simultaneous high magnification in extension, a condition not normally realizable with a multiple-beam equipment employing optical flats.