Scalable inline scanning deflectometry using unit-under-test motion

Achieving efficient and accurate optical surface measuring has been a longstanding goal in various industries. Deflectometry meets these demands by eliminating the need for null optics, offering a wide dynamic range for slope measurements using a simple setup that includes a camera, a screen as the light source, and a test sample. In deflectometry, however, the screen size limits the optical testing of flat or convex surfaces. This paper introduces a boundless light source method that measures surface slopes using two fixed line sources with known positions. Unlike conventional deflectometry, where the test sample remains stationary while the sinusoidal pattern displayed on the screen is shifting, the proposed technique involves moving the test sample along a single axis while keeping the sources and camera stationary. Local slopes are obtained by utilizing the relative position of the camera, light sources, and the testing sample. The reconstructed map from the algorithm promisingly shows below 20nm RMS surface error and 15urad RMS slope error compared with the Interferometry measurement when measuring a 2-inch flat mirror. This approach allows for scalable surface measurements, with potential applications in measuring large flat mirrors, such as those used in heliostat systems. Additionally, this method can be used as in-line metrology by integrating the linear movement of the setup or the planetary trajectory motion.