Fast and accurate Deflectometry with Crossed Fringes

Abstract

Phase Measuring Deflectometry (PMD) acquires the two components of the local surface gradient via a sequence of two orthogonal sinusoidal fringe patterns that have to be displayed and captured separately. We will demonstrate that the sequential process (different fringe directions, phase shifting) can be completely avoided by using a cross fringe pattern. With an optimized Fourier evaluation, high quality data of smooth optical surfaces can be acquired within one single shot. The cross fringe pattern allows for one more improvement of PMD: we will demonstrate a novel phase-shift technique, where a one-dimensional N-phase shift allows for the acquisition of the two orthogonal phases, with only N exposures instead of 2N exposures. So, PMD can be implemented by a one-dimensional translation of the fringe pattern, instead of the common two-dimensional translation, which is quite useful for certain applications.