Extreme adaptive optics testbed: high contrast measurements with a MEMS deformable mirror

Abstract

ABSTRACT"Extreme" adaptive optics systems are optimized for ultra-high-contrast applications, such as ground-based extrasolar planet detection. The Extreme Adaptive Optics Testbed at UC Santa Cruz is being used to investigate and develop technologies for high-contrast imaging, especially wavefront control. We use a simple optical design to minimize wavefront error and maximize the experimentally achievable contrast. A phase shifting diffraction interferometer (PSDI) measures wavefront errors with sub-nm precision and accuracy for metrology and wavefront control. Previously, we have demonstrated RMS wavefront errors of <1.5 nm and a contrast of >10 7 over a substantial region using a shaped pupil without a deformable mirror. Current work includes the installation and characterization of a 1024-actuator Micro-Electro-Mechanical-Systems (MEMS) deformable mirror, manufactured by Boston Micro-Machines for active wavefront control. Using the PSDI as the wavefront sensor we have flattened the deformable mirror to <1 nm within the controllable spatial frequencies and measured a contrast in the far field of > 10 6. Consistent flattening required testing and characterization of the individual actuator response, including the effects of dead and low-response actuators. Stability and repeatability of the MEMS devices was also tested. Ultimately this testbed will be used to test all aspects of the system architecture for an extrasolar planet-finding AO system.

The extreme adaptive optics testbed at UCSC: current results and coronagraphic upgrade

“…9 Earlier work with the MEMS device has been previously presented. [10][11][12][13] Here we discuss our flattening procedure and our latest and best contrast results with our MEMS.…”

Precise wavefront correction with an unbalanced nulling interferometer for exo-planet imaging coronagraphs

“…Control accuracy of a DM was demonstrated to a level of λ/10 000 rms (e.g. Brown et al 2003;Evans et al 2005), while some commercial wavefront sensors were reported to achieve absolute wavefront measurement accuracies of λ/1000 rms by the conventional Shack-Hartmann method (e.g. HASO HP 26 from Imagine Optic).…”

High-Contrast Imaging using Adaptive Optics for Extrasolar Planet Detection

“…In imaging mode, the reference pinhole is replaced with a CCD camera and only the probe beam is used. Further information about contrast measurements can be found in prior works [26,63] and Chapter 4. In interferometry mode, the testbed becomes an extremely accurate optical metrology system.…”

“…Errors in each of these tasks leads to errors in performance and these are summarized in an error budget. Preliminary work with the MEMS device, including some of the engineering challenges leading up to this result, have been presented in prior works [71,63,61]. A complete inventory of these difficulties, together with our mitigation techniques, is included here.…”