A double-pass Fizeau interferometer system for measuring the figureerror of large synchrotron optics

摘要

A laser Fizeau interferometer system has been developed to characterize the figure error of large synchrotron X-ray mirrors using double-pass geometry. This opto-mechanical assembly comprises integrated rotation and translation stages to control: the output angle of the Fizeau interferometer; the surface normal of the optic under test; and the orientation of a high quality (λ/100) retro-reflector. To negate the effects of gravitational deformations, the system can measure long optics (up to 1.5m in length) in the geometry (sideward, downward, or upward facing) in which they will ultimately be used on a synchrotron beamline. The system has been designed to minimize environmental noise and enable the measurement geometry to be changed quickly and safely. Compared to complementary techniques, including slope profilers such as the Diamond-NOM, surface height data from the Fizeau system can be obtained more rapidly (<1 minute). This makes the technique ideally suited to investigate the many degrees of freedom of adaptive optics, including piezo bimorph mirrors. The shape of such optics can also be monitored in real time to observe the dynamic effects of the surface in response to applied voltages. Results are presented to illustrate system performance, including repeatability levels. Calibration of the reference surfaces and the required environmental conditions are also discussed.