A Near-Infrared Pyramid Wavefront Sensor for the MMT

TL;DR

This paper presents the development and testing of a near-infrared pyramid wavefront sensor using a SAPHIRA detector for the MMT, aiming to enhance adaptive optics performance and sky coverage.

Contribution

It introduces a novel NIR PyWFS with a SAPHIRA detector, including its characterization, performance testing in a closed-loop AO testbed, and its potential impact on adaptive optics systems.

Findings

SAPHIRA detector reaches sub-electron read noise at high gain.

The NIR PyWFS is expected to significantly improve sky coverage.

Closed-loop AO performance of the SAPHIRA has been successfully tested.

Abstract

The MMTO Adaptive optics exoPlanet characterization System (MAPS) is an ongoing upgrade to the 6.5-meter MMT Observatory on Mount Hopkins in Arizona. MAPS includes an upgraded adaptive secondary mirror (ASM), upgrades to the ARIES spectrograph, and a new AO system containing both an optical and near-infrared (NIR; 0.9-1.8 um) pyramid wavefront sensor (PyWFS). The NIR PyWFS will utilize an IR-optimized double pyramid coupled with a SAPHIRA detector: a low-read noise electron Avalanche Photodiode (eAPD) array. This NIR PyWFS will improve MAPS's sky coverage by an order of magnitude by allowing redder guide stars (e.g. K & M-dwarfs or highly obscured stars in the Galactic plane) to be used. To date, the custom designed cryogenic SAPHIRA camera has been fully characterized and can reach sub-electron read noise at high avalanche gain. In order to test the performance of the camera in a closed-loop environment prior to delivery to the observatory, an AO testbed was designed and constructed. In addition to testing the SAPHIRA's performance, the testbed will be used to test and further develop the proposed on-sky calibration procedure for MMTO's ASM. We will report on the anticipated performance improvements from our NIR PyWFS, the SAPHIRA's closed-loop performance on our testbed, and the status of our ASM calibration procedure.