On-sky, real-time optical gain calibration on MagAO-X using incoherent speckles

TL;DR

This paper presents a real-time, on-sky method for calibrating optical gain in the MagAO-X adaptive optics system, improving wavefront correction accuracy for exoplanet imaging.

Contribution

It introduces a novel high-temporal frequency probing technique to measure optical gain on-sky, enhancing calibration accuracy during observations.

Findings

Optical gain depends on Strehl Ratio.

High-temporal frequency probes effectively measure optical gain.

Calibration improves wavefront correction fidelity.

Abstract

The next generation of extreme adaptive optics (AO) must be calibrated exceptionally well to achieve the desired contrast for ground-based direct imaging exoplanet targets. Current wavefront sensing and control system responses deviate from lab calibration throughout the night due to non linearities in the wavefront sensor (WFS) and signal loss. One cause of these changes is the optical gain (OG) effect, which shows that the difference between actual and reconstructed wavefronts is sensitive to residual wavefront errors from partially corrected turbulence. This work details on-sky measurement of optical gain on MagAO-X, an extreme AO system on the Magellan Clay 6.5m. We ultimately plan on using a method of high-temporal frequency probes on our deformable mirror to track optical gain on the Pyramid WFS. The high-temporal frequency probes, used to create PSF copies at 10-22 lambda /D, are already routinely used by our system for coronagraph centering and post-observation calibration. This method is supported by the OG measurements from the modal response, measured simultaneously by sequenced pokes of each mode. When tracked with DIMM measurements, optical gain calibrations show a clear dependence on Strehl Ratio, and this relationship is discussed. This more accurate method of calibration is a crucial next step in enabling higher fidelity correction and post processing techniques for direct imaging ground based systems.