Parasitic reflection elimination using binary pattern in phase measuring deflectometry

Phase measuring deflectometry (PMD) is a high precision measurement method for optical surface shape, which has been used in the fabrication and application of high quality optical element. For the on-line surface measurement of transparent optical elements in the laser inertial confinement fusion facility, PMD is a very promising method. However, the parasitic reflection from the rear surface is an existing problem for PMD to measure transparent element. In this paper, a parasitic reflection eliminating method with the use of binary pattern is proposed, the principle of which is described in detail. The ability of the proposed method to extract the front surface information is demonstrated by the numerical simulation. And the proposed method is used to measure a transparent window glass with a thickness of about 10 mm. The surface shape result shows a good agreement with the interferometer data with a sub-wavelength level accuracy.