Optical system for closed-loop testing of adaptive optic convex mirror

Steward Observatory is building a deformable f/15 secondary mirror for the 6.5 m Multiple Mirror Telescope conversion that will compensate for atmospheric turbulence. A potential difficulty of an adaptive secondary mirror is the ability to verify the commanded mirror shapes of a large convex deformable surface. A new optical design is presented to test the deformable mirror's closed loop control system by optically projecting an artificial star to simulate starlight in the actual telescope. An optical fiber fed interferometer has been incorporated into the design to measure the deformable mirror's ability to compensate for atmospheric turbulence by measuring the wavefront through an atmospheric turbulence generator. The test system has been designed to verify the control system by fitting into both a laboratory test structure as well as the telescope support structure itself. The optical design relies on two wavelength computer generated holograms used to remove spherical aberration as well as aid in the alignment of the test system optics by projecting alignment patterns.