Calibration and performance evaluation of a monomorph deformable mirror

Abstract

To achieve diffraction-limited performance with a 50 cm solar telescope at the Udaipur solar observatory the development of a high-order adaptive optics (AO) system is currently in progress. The system includes a monomorph deformable mirror (MDM) with 85 actuators and 35 mm diameter that servers as a wavefront corrector. Prior to using the MDM in an AO system, the MDM is calibrated, and its performance is evaluated using a laboratory source. Aim is to determine the extent of intrinsic aberrations of the MDM and the optimum voltage vector that makes the MDM optically flat, so that the MDM can be used in the optical setup without introducing any aberrations. Here, we present the details of the calibration of the MDM and its performance in correcting a static error. For this purpose, Fizeau interferometry and Shack–Hartmann wavefront sensing (SHWFS) methods are employed for sensing the wavefront distortions. A static defocus error is corrected in closed-loop such that the rms wavefront error is reduced from nearly 600 nm to about 20 nm in less than ten iterations using a laser interferometer and the SHWFS. Our study shows the extent of intrinsic aberrations of the MDM has to be factored in an operational AO system.

Keywords

• Adaptive optics
• Wavefront corrector
• Deformable mirror
• SHWFS