High Sensitivity Wavefront Sensing with a non-linear Curvature Wavefront Sensor

TL;DR

This paper introduces a non-linear curvature wavefront sensor that approaches the fundamental sensitivity limit, enabling high-precision adaptive optics correction for bright stars, crucial for exoplanet imaging.

Contribution

It presents a novel non-linear wavefront sensing method that significantly improves sensitivity over traditional linear sensors, leveraging wavefront coherence for enhanced adaptive optics performance.

Findings

Achieves 100 nm RMS wavefront error on 8-m telescope with a 13th magnitude star.

Approaches the diffraction limit sensitivity set by fundamental physics.

Suitable for high-precision adaptive optics in exoplanet and disk imaging.

Abstract

A new wavefront sensing approach, derived from the successful curvature wavefront sensing concept but using a non-linear phase retrieval wavefront reconstruction scheme, is described. The non-linear curvature wavefront sensor (nlCWFS) approaches the theoretical sensitivity limit imposed by fundamental physics by taking full advantage of wavefront spatial coherence in the pupil plane. Interference speckles formed by natural starlight encode wavefront aberrations with the sensitivity set by the telescope's diffraction limit lambda/D rather than the seeing limit of more conventional linear WFSs. Closed-loop adaptive optics simulations show that with a nlCWFS, a 100 nm RMS wavefront error can be reached on a 8-m telescope on a mV = 13 natural guide star. The nlCWFS technique is best suited for high precision adaptive optics on bright natural guide stars. It is therefore an attractive technique to consider for direct imaging of exoplanets and disks around nearby stars, where achieved performance is set by wavefront control accuracy, and exquisite control of low order aberrations is essential for high contrast coronagraphic imaging. Performance gains derived from simulations are shown, and approaches for high speed reconstruction algorithms are briefly discussed.