Integrated Ray Tracing simulation of the SCOTS surface measurement test for the GMT Fast Steering Mirror Prototype

Software Configurable Optical Testing System (SCOTS) is one of relatively new optical testing methods for large optical surfaces and uses the principle of Phase Measuring Deflectometry (PMD). A camera captures images of the target surface illuminated by a light source screen with patterns. Then, the surface slope and height are obtained by camera image analysis. In the meantime, Integrated Ray Tracing (IRT) concept was developed for the simultaneous end-to-end imaging and radiometric performance simulation of space instruments. It incorporates a light source, medium, target and observing instrument into single computation environment for real scale ray tracing. In this study, we combined these two techniques for the development of an optical testing simulation model applicable to testing the secondary mirror (M2) of Giant Magellan Telescope (GMT). Using the IRT SCOTS model, we simulated SCOTS test runs and reconstructed its surface slopes and heights from the simulated image data. The result shows 1.05 nm rms in difference between the input and reconstructed surface heights. It demonstrates the high fidelity of the suggested IRT approach showing nanometer level numerical accuracy and therefore it shows the potential applicability of the IRT simulation technique to SCOTS test method for large precision optical surfaces.