Study on eliminating the effect of parasitic reflection on deflectometry measurement of planar optical element surface figure

Phase measuring deflectometry (PMD) with structured light projection and phase-shifting technique is a highly accurate optical surface measuring method. For surface shape measurement of transparent planar elements, PMD suffers from parasitic reflection. To avoid the unwanted effect of parasitic reflection, a method based on fringe frequency tuning and Fourier-transform is introduced in this paper. Numerical simulations and experiments are both conducted to evaluate the performance of the proposed method. An optical planar element with a thickness of 24.5mm is measured, and measurement error is within 200nm PV.