Three-dimensional micro-topography by Talbot-projected fringes

Abstract

Implementation of a structured light projection technique for measuring the relief of objects, or object areas, of micrometric size (approximately 500 μm x 500 μm), is described. It is well-known that when a fringe pattern is projected on an object, the fringes are deformed according to the topography of its surface. This deformed fringe pattern is a modulated optical signal that allows us to measure the relief of the object. Through one of the oculars of a stereomicroscope, previously focused on the object under study, the fringe pattern of one the Talbot self-image is projected. The deformed fringe patterns are observed by the other ocular, in which a CCD camera is mounted to digitize them. Digitized fringe patterns are demodulated by means of a second virtual reference grating. As a result, a moire fringe pattern is obtained delivering a wrapped phase map when is digitally processed by means of a phase recover technique. Phase recovery techniques for obtaining the wrapped phase maps are phase-shifting and spatial phase synchronous. Experimental results and the conditions, under which the topography of an object section is determined, are shown. Also, comparisons over quality between the phase recovery techniques are discussed.