### Abstract

The Nonlinear Curvature Wavefront Sensor (nlCWFS), first proposed by Guyon, determines wavefront shape from images of a reference beacon in a number of planes between the pupil and focal plane of a telescope. We describe a new algorithm that rapidly recovers the low-order aberrations accurately enough to allow practical use of the nlCWFS in an adaptive optics (AO) system. The algorithm was inspired by refractive strong scintillation in the interstellar medium, which behaves similarly to near-pupil linear curvature focusing, but over larger scales. The refractive component is extracted from the speckled images by binning with the lowest-order aberrations being additionally estimated through the use of first and second distribution moments. The linearity of the refractive scintillation process allows us to use a reconstructor matrix to compute an estimate of the pupil wavefront. The resulting wavefront estimate is then applied in reverse to a deformable mirror (DM), reducing the nonlinearity to the point that a single update phase retrieval algorithm such as a multi-plane version of Gerchberg-Saxton (GS) can be used to estimate the remaining wavefront error (WFE). An AO simulation of a 1.5 m telescope, a 16x16 actuator DM, and four image planes show that the scintillation algorithm works, reducing ∼800 nm rms WFE to ∼ 40 nm, well below the fitting error (∼90 nm) in closed loop. Once corrected to this level, the image planes still show a great deal of information that can then be used with a single-update wavefront retrieval algorithm. A couple simple variants of GS are suggested, including one that can be parallelized for each camera and run in parallel with the scintillation algorithm. A Monte Carlo study will be required to determine the best approach.

Original language | English (US) |
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Title of host publication | Adaptive Optics Systems VI |

Editors | Dirk Schmidt, Laura Schreiber, Laird M. Close |

Publisher | SPIE |

ISBN (Print) | 9781510619593 |

DOIs | |

Publication status | Published - Jan 1 2018 |

Externally published | Yes |

Event | Adaptive Optics Systems VI 2018 - Austin, United States Duration: Jun 10 2018 → Jun 15 2018 |

### Publication series

Name | Proceedings of SPIE - The International Society for Optical Engineering |
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Volume | 10703 |

ISSN (Print) | 0277-786X |

ISSN (Electronic) | 1996-756X |

### Other

Other | Adaptive Optics Systems VI 2018 |
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Country | United States |

City | Austin |

Period | 6/10/18 → 6/15/18 |

### Fingerprint

### Keywords

- Adaptive Optics
- Curvature
- Nonlinear
- Refractive Scintillation
- Scintillation
- Strong Scattering
- Wavefront Sensing

### ASJC Scopus subject areas

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Computer Science Applications
- Applied Mathematics
- Electrical and Electronic Engineering

### Cite this

*Adaptive Optics Systems VI*[107035Q] (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 10703). SPIE. https://doi.org/10.1117/12.2313760