High-bandwidth interferometer for real-time measurement of deformable mirrors

We report on the design and fabrication of a high bandwidth interferometer suitable for real- time measurement of the figure of a deformable mirror. The design allows for measurement of mirror figure in terms of optical path differences (OPD) between the surface of the mirror and a static reference wavefront. Measurements are made on a 31 by 31 square grid. This instrument is relevant for atmospheric adaptive optics systems because it provides a method for accurately monitoring the figure of a deformable mirror during real-time compensation of atmospheric turbulence. Measured values of OPD on the mirror surface are output in digital form at approximately 10 kHz and can be used as a feedback signal in a digital control-loop for driving the deformable mirror. The system uses a common 4-bucket or 4-measurement interferometric algorithm to compute OPD. The maximum measurable OPD is +/- 7.5 waves. Tests of the completed interferometer indicate that it can routinely measure the dynamic changes in figure of an optical mirror. Preliminary tests indicate that the measurements are accurate to approximately (lambda) /25.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.