Characterizing deformable mirrors for the MagAO-X instrument

TL;DR

This paper details the characterization of deformable mirrors used in the MagAO-X adaptive optics system, demonstrating their surface correction capabilities and impact on wavefront error and image quality.

Contribution

It provides detailed surface characterization of the DMs and assesses their effectiveness in correcting wavefront errors in the MagAO-X system.

Findings

Tweeter DM achieves 6.9 nm RMS surface flatness

Woofer DM achieves 2.2 nm RMS surface

System corrects wavefront error to 18.7 nm RMS, achieving Strehl ratio of 0.94

Abstract

The MagAO-X instrument is a new extreme adaptive optics system for high-contrast imaging at visible and near-infrared wavelengths on the Magellan Clay Telescope. A central component of this system is a 2040-actuator microelectromechanical deformable mirror (DM) from Boston Micromachines Corp. that operates at 3.63 kHz for high-order wavefront control (the tweeter). Two additional DMs from ALPAO perform the low-order (the woofer) and non-common-path science-arm wavefront correction (the NCPC DM). Prior to integration with the instrument, we characterized these devices using a Zygo Verifire Interferometer to measure each DM surface. We present the results of the characterization effort here, demonstrating the ability to drive tweeter to a flat of 6.9 nm root mean square (RMS) surface (and 0.56 nm RMS surface within its control bandwidth), the woofer to 2.2 nm RMS surface, and the NCPC DM to 2.1 nm RMS surface over the MagAO-X beam footprint on each device. Using focus-diversity phase retrieval on the MagAO-X science cameras to estimate the internal instrument wavefront error (WFE), we further show that the integrated DMs correct the instrument WFE to 18.7 nm RMS, which, combined with a 11.7% pupil amplitude RMS, produces a Strehl ratio of 0.94 at H$\alpha$.