# The Asymmetric Pupil Fourier Wavefront Sensor

**Authors:** Frantz Martinache  
**arXiv:** [1303.6678](https://arxiv.org/abs/1303.6678)  
**Date:** 2013-03-26  
**Summary page:** https://www.summarizepaper.com/en/paper/1303.6678v1/

## Key points

- Wavefront sensing is important in astronomy for improving image quality by correcting for atmospheric turbulence
- Frantz Martinache introduces a new approach to wavefront sensing called the Asymmetric Pupil Fourier Wavefront Sensor (APF-WFS)
- APF-WFS relies on Fourier analysis of a single conventional direct image and can be used in the high Strehl ratio regime where the relation between phase measured in Fourier plane and wavefront errors can be linearized
- To use APF-WFS, two conditions must be met: wavefront errors must be small and some asymmetry must be introduced into the pupil using a mask to make it solvable
- Simulations show that APF-WFS can improve Strehl ratio from 50% to over 90% in just a few iterations with excellent photon noise sensitivity properties
- APF-WFS offers an efficient way to correct for atmospheric turbulence and improve image quality, making it a promising candidate for future implementation in adaptive optics systems.

## Summary

In the field of astronomy, wavefront sensing is a crucial technique for improving image quality by correcting for atmospheric turbulence. Frantz Martinache introduces a novel approach to wavefront sensing called the Asymmetric Pupil Fourier Wavefront Sensor (APF-WFS) in this paper. The technique relies on the Fourier analysis of a single conventional direct image and can be used in the high Strehl ratio regime where the relation between the phase measured in the Fourier plane and wavefront errors in the pupil can be linearized. This was previously demonstrated with generalized closure-phase or kernel-phase. To use APF-WFS as presented, two conditions must be met: (1) wavefront errors must be kept small, on the order of one radian or less; and (2) some asymmetry must be introduced into the pupil using a mask to make it solvable. Simulations show that APF-WFS can improve Strehl ratio from 50% to over 90% in just a few iterations with excellent photon noise sensitivity properties. This suggests that on-sky close loop APF-WFS is possible with an extreme adaptive optics system. The paper's contribution lies in its introduction of an innovative method for wavefront sensing that has significant potential for improving astronomical imaging capabilities. By relying on Fourier analysis and introducing asymmetry into the pupil, APF-WFS offers an efficient way to correct for atmospheric turbulence and improve image quality. The simulations presented demonstrate its effectiveness, making it a promising candidate for future implementation in adaptive optics systems.