Surface shape measurement of transparent planar elements with phase measuring deflectometry

Abstract

Phase measuring deflectometry (PMD) with structured light projection and phase-shifting technique is a highly accurate optical surface measuring method based on the law of reflection. Generally, for surface shape measurement of transparent planar elements, PMD suffers from parasitic reflection. To avoid the unexpected effect of parasitic reflection, a method based on fringe frequency tuning and Fourier-transform is introduced. Numerical simulations and experiments are both conducted to evaluate the performance of the proposed method. Experiment results are shown. Surface figures measured using the proposed method are compared with those measured using traditional phase-shifting algorithm and Fizeau interferometer. Both an optical planar element with a thickness of 24.5 mm and a planar window glass with a thickness of 10 mm are measured. For the optical element, the proposed method is accurate and the measurement error is within 200-nm PV. For window glass, the proposed method yields a better surface figure than the traditional phase-shifting algorithm does.