Surface Topography of Non-optical Surfaces by Projected Interference Fringes

Abstract

IN the light slit microscope of Schmaltz¹ a narrow slit of light is projected obliquely onto an irregular surface, and the trace of the slit, viewed normally through a microscope, provides a section of the surface to a scale depending on the angle of incidence of the light. This technique has the disadvantages that (a) there is only a single slit image, which must therefore be made to traverse the surface, and (b) there is very little focal depth in the slit image if it is made narrow enough. If the width of the slit is to be d it must be projected with numerical aperture α = λ/d and the focal depth is approximately λ/α², where λ is the wavelength of the light.