Pupil plane wavefront sensing for extended and 3D sources

TL;DR

This paper reviews pupil plane wavefront sensing techniques for extended and 3D sources, highlighting the INGOT WFS as an equivalent to the Pyramid sensor for Laser Guide Stars and proposing methods to improve SNR and photon utilization.

Contribution

It introduces the application of the INGOT WFS to extended and 3D sources, comparing it to the Pyramid sensor, and suggests strategies to enhance wavefront sensing performance.

Findings

INGOT WFS is equivalent to the Pyramid for Laser Guide Stars.

Features of the reference are not invariant across the pupil for extended sources.

Dark WFS approach can improve SNR and photon efficiency.

Abstract

The basic outline of a pupil plane WaveFront Sensor is reviewed taking into account that the source to be sensed could be different from an unresolved source, i.e. it is extended, and that it could deploy also in a 3D fashion, enough to exceed the field's depth of the observing telescope. Under these conditions it is pointed out that the features of the reference are not invariant for different position on the pupil and it is shown that the INGOT WFS is the equivalent of the Pyramid for a Laser Guide Star. Under these conditions one can imagine to use a Dark WFS approach to improve the SNR of such a WFS, or to use a corrected upward beam in order to achieve a better use of the LGS photons with respect to an ideal Shack-Hartmann WFS.