Alternative pyramid wavefront sensors

Maaike Van Kooten,Colin Bradley,Jean Pierre Veran

doi:10.1117/1.jatis.3.2.029001

Maaike Van Kooten, Colin Bradley + Show 1 more

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https://doi.org/10.1117/1.jatis.3.2.029001

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Abstract

The feasibility of a lenslet-based pyramid wavefront sensor (L-PWFS) and a double roof prism-based PWFS (DR-PWFS) as alternatives to a classical PWFS are investigated in this work. Traditional PWFSs require shallow angles and strict apex tolerances, making them difficult to manufacture. Lenslet arrays and roof prisms, on the other hand, are both common optical components that can be used as a PWFS. Characterizing these alternative pyramids and understanding how they differ from a traditional pyramid will allow the PWFS to become more widely used. The sensitivity of the SUSS microOptics 300-4.7 array and two ios Optics roof prisms are compared with a double PWFS (D-PWFS), as well as the simulated performance of an idealized PWFS for varying amounts of modulation and induced wavefront error. In response to low-order Zernike modes, the L-PWFS shows much lower performance and quicker saturation for large amounts of wavefront errors. The DR-PWFS, on the other hand, performs as well as the D-PWFS for the tests conducted. We conclude from this that the DR-PWFS does provide a feasible alternative to the classical pyramid in a range of applications.

Highlights

The pyramid wavefront sensor (PWFS), proposed in 1996 as an alternative to the Shack–Hartmann wavefront sensor (SHWFS), has been shown to be more sensitive, yielding better performance for a given guide-star magnitude[1] and a significant gain in limiting magnitude[2] compared with the SHWFS
The three PWFS prototypes: SUSS microOpitcs 300-4.7 lenslet array, two iosOptics roof prisms as a double roof prism-based PWFS (DR-PWFS), and a double PWFS (D-PWFS) were tested on the wavefront sensing bench at NRC-Herzberg
The PWFS is less sensitive to these small aberrations as they are blurred out by the modulation pattern. Combining this with the effects of the optical element of the pyramid, and the deformable mirror (DM) fitting error, much of the difference between the theoretical and experimental curves can be explained. These results show the lenslet-based pyramid wavefront sensor (L-PWFS) to have the worst behavior due to the optical quality of the lenslet array itself

Summary

Introduction

The pyramid wavefront sensor (PWFS), proposed in 1996 as an alternative to the Shack–Hartmann wavefront sensor (SHWFS), has been shown to be more sensitive, yielding better performance for a given guide-star magnitude[1] and a significant gain in limiting magnitude[2] compared with the SHWFS. To create a PWFS, the optical device—a glass pyramid—is placed in the image plane of the system, with the spot focused on the pyramid’s apex. The light is divided into four quadrants and imaged onto a detector located at the pupil plane. The pixels on the detector split the pupil into subapertures (done on all four images of the pupil) analogous to how each lenslet array splits the pupil in the SHWFS. As the light interacts with the edges of the pyramid, a modified knife edge test is performed. All four pupils are full images of the telescope aperture and encode information about the incoming wavefront

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Conclusion