3D shape measurement of the aspheric mirror by advanced phase measuring deflectometry

An advanced Phase Measuring Deflectometry(PMD) is proposed to measure the three dimensional (3D) shape of the aspheric mirror. In the measurement process, a liquid crystal display(LCD)screen displaying sinusoidal fringe patterns and a camera observing the fringe patterns reflected via the tested mirror, are moved along the tested mirror optical axis, respectively. At each movement position, the camera records the fringe patterns of the screen located at two different positions. Using these fringe patterns, every camera pixels can find a corresponding point on the tested mirror and gets its coordinate and slope. By integrating, the 3D shape of the tested mirror can be reconstructed. Compared with the traditional PMD, this method doesn???t need complex calibration and can measure the absolute height of the aspheric mirror which has large range of surface geometries unambiguously. Furthermore, this method also has strong anti-noise ability. Computer simulations and preliminary experiment validate the feasibility of this method.