The infrared low order sensor (IRLOS) upgrade project was performed at VLT UT4 in 2021. The goal was to expand the sky coverage of GALACSI Narrow-Field Mode (NFM) by increasing the sensitivity of IRLOS from Jmag < 15 to Jmag > 17. The baseline approach is to perform low-order wavefront sensing (LO WFSing) with a 2x2 Shack-Hartmann wavefront sensor (SH WFS) operating in the J+H band. With this upgrade, a new full-pupil mode was additionally introduced to IRLOS to address the faintest end of the magnitude range by concentrating the photons from the full aperture in a single point spread function (PSF). Within this scope, the approach called the LInearized Focal-plane Technique (LIFT) was proposed for slow truth-sensing at low flux. It is based on introducing the known amount of astigmatic phase diversity and is implemented by inserting a cylindrical lens into the IRLOS filter wheel. LIFT enables the retrieval of LO modes such as tip/tilt, defocus, and astigmatism from a single focal-plane PSF of a faint natural guide star (NGS) target up to Jmag = 19.
However, the existing baseline solution with SH WFS provided reliable operation of IRLOS at Jmag = 19, and hence the full-pupil mode is currently deprecated along with the idea of using LIFT. Nevertheless, experimental verification of this method was carried out both on an optical bench and on-sky. In this work, we revisit the collected experimental results and provide additional analysis of them. We also discuss the applicability of this method in realistic conditions and the limitations associated with the on-sky operations at AOF. We also explore the idea of augmenting LIFT with Machine Learning-based (ML) approaches in an attempt to provide a more accurate reconstruction.
| Subject : | : | oral |
| Topics | : | Focal-plane WFSensing |
| PDF version | : |  PDF version |
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