In-situ full-aperture measurement of large optical surfaces based on extended virtual source stitching deflectometry

Phase measuring deflectometry (PMD) is widely used for in-situ optical surface measurement, but its full-aperture capability is limited by the finite screen size when measuring large apertures. This paper proposes an extended virtual source stitching PMD (EVSS-PMD) method for in-situ full-aperture measurement. By translating the screen to different positions, the finite screen is extended into a larger virtual source. Since the camera and test surface remain fixed, all sub-apertures share a common coordinate frame, eliminating the need for multi-view point-cloud registration. To compensate for residual overlap mismatch caused by screen pose uncertainty, an affine compensation method is developed based on geometric analysis of the virtual source system. Experiments on a 220-mm-aperture flat mirror and a 340-mm-aperture off-axis parabolic mirror demonstrate smooth full-aperture reconstruction, with measurement accuracy of tens of nanometers relative to a ZYGO interferometer.