Performance of a MEMS reflective wavefront sensor

An all reflective Shack Hartmann style wavefront sensor has been developed using a Sandia National Laboratory segmented Micro-Electro-Mechanical (MEM) deformable mirror. This wavefront sensor is presently being explored for use with adaptive optics systems at the Naval Prototype Optical Interferometer and other experimental adaptive systems within the Naval Research Laboratory. The 61 MEM mirror segments are constructed in a hexagonal array and each segment can be constructed with either flat or optically powered surfaces. The later allows each mirror segment to bring its subaperture of light to a focus on an imaging array, creating an array of spots similar to a Shack Hartmann. Each mirror segment has tip, tilt and piston functionality to control the position of the focused spot such that measurement of the applied voltage can be used to drive a deformable mirror. As the system is reflective and each segment is controllable, this wavefront sensor avoids the light loss associated with refractive optics and has larger dynamic range than traditional Shack Hartmann wavefront sensors. This wavefront sensor can detect large magnitude aberrations up to and beyond where the focused spots overlap, due to the ability to dither each focused spot. Previous publications reported on this novel new technique and the electrical specifications, while this paper reports on experiments and analysis of the open-loop performance, including repeatability and linearity measurements. The suitability of using the MEM deformable mirror as a high dynamic range reflective wavefront sensor will be discussed and compared to current wavefront sensors and future work will be discussed.