Time-resolved pyramid wavefront sensor experimental results on REVOLT

Abstract

New SPAD-based, single-photon, fast-timing detectors are becoming increasingly attractive for astronomy. These detectors enable a new modality for wavefront sensing: photon time-of-arrival. Pyramid wavefront sensors (PWFS) offer excellent sensitivity, but suffer from non-linear behavior. This is typically mitigated by modulating the guide star point spread function (PSF) around the pyramid’s apex, which improves linearity but reduces sensitivity. We are developing a Time-Resolved Pyramid Wavefront Sensor (TR-PWFS) that leverages the high temporal resolution of our SPAD-based detectors to break the modulation cycle into discrete time frames. Our analysis shows that different controlled modes are best sensed at specific points along the modulation path. By assigning weights to each frame based on its information content for a given mode, we improve the signal-to noise ratio (SNR) of the PWFS measurement, especially for low-order modes, for which the most information is captured during transitions between pyramid faces. This frame-weighting strategy improves robustness to detector and photon noise and allows for higher AO performance for a given guide star magnitude, or for the use of fainter guide stars for a given level of performance, thus expanding adaptive optics sky coverage. In this paper, we will present on-sky results of the TR-PWFS on the PWFS arm of the REVOLT AO bench using a commercial SPAD-based camera with the aim of running 500Hz by synthesizing 24 frames per modulation cycle requiring a readout rate of 12kHz.