Measurement of the Thickness of Transparent Films with the Light-Profile Microscope

Abstract

THE light-profile microscope technique, described by Tolansky¹, has been adapted by us for the determination of the optical thickness of relatively thick transparent films. A transparent film, bounded by media with refractive indices differing from that of the film, has two reflecting surfaces; when observed with a light-profile microscope these two surfaces produce a double image, from the separation of which it is relatively easy to derive the ratio t/μ in which t is the thickness and μ the refractive index. This is of much value in so far as direct interferometry, using, for example, fringes of equal chromatic order, gives the value μt. The combined methods thus give both μ and t.