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Assessing phase reconstruction accuracy for different nonlinear curvature wavefront sensor configurations

JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS 2023年第4期9卷

作者： Letchev, Stanimir Crass, Jonathan Crepp, Justin R. Univ Notre Dame Dept Phys & Astron Notre Dame IN 46556 USA Ohio State Univ Dept Astron Columbus OH USA

The nonlinear curvature wavefront sensor (nlCWFS) offers improved sensitivity for adaptive optics systems compared with existing WFSs, such as the ShackHartmann. The nominal nlCWFS design uses a series of imaging planes offset from the pupil along the optical propagation axis as inputs to a numerically iterative reconstruction algorithm. Research into the nlCWFS has assumed that the device uses four measurement planes configured symmetrically around the optical system pupil. This assumption is not strictly required. In this paper, we perform the first systematic exploration of the location, number, and spatial sampling of measurement planes for the nlCWFS. Our numerical simulations show that the original, symmetric four-plane configuration produces the most consistently accurate results in the shortest time over a broad range of seeing conditions. We find that the inner measurement planes should be situated past the Talbot distance corresponding to a spatial period of r 0. The outer planes should be large enough to fully capture the field intensity and be situated beyond a distance corresponding to a Fresnel-number-scaled equivalent of Z approximate to 50 km for a D = 0.5 m pupil with lambda= 532 nm. The minimum spatial sampling required for diffraction-limited performance is 4 to 5 pixels per r 0 as defined in the pupil plane. We find that neither three-plane nor five-plane configurations offer significant improvements compared with the original design. These results can impact future implementations of the nlCWFS by informing sensor design.

关键词： wavefront sensing adaptive optics wavefront reconstruction algorithms

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Centroiding and Extraction of Tip/Tilt Information from Nonlinear Curvature wavefront Sensor Measurements 9

Centroiding and Extraction of Tip/Tilt Information from Nonl...

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Conference on Adaptive Optics Systems IX

作者： Abbott, Caleb G. Crepp, Justin R. Letchev, Stanimir O. Smith, Connor M. Univ Notre Dame Phys & Astron Notre Dame IN 46556 USA Max Planck Inst Astron Konigstuhl 17 D-69117 Heidelberg Germany

ISBN: (纸本)9781510675186;9781510675179

The nonlinear curvature wavefront sensor (nlCWFS) uses multiple (typically four) out-of-focus images to reconstruct the phase and amplitude of a propagating light beam. Because these images are located between the pupil and focal planes, they contain tip/tilt information. Rather than using a separate sensor to measure image locations, it would be beneficial to extract tip/tilt information directly and routinely as part of the reconstruction process. In the presence of atmospheric turbulence, recovering precise centroid offsets for each out-of-focus image becomes a dynamic process as image structure is altered by changing aberrations. We examine several tip/tilt extraction methods and compare their precision and accuracy using numerical simulations. We find that the nlCWFS outer measurement planes confer more accurate and reliable tip/tilt information than the inner measurement planes, due to their larger geometric lever arm. However, in practice, finite field of view (detector region of interest) effects bias tip/tilt retrieval when using the outer planes due to diffraction. Using knowledge of the z-distance to each plane, we find that applying a best-fit linear model to multiple image centroid locations can offer fast and accurate tip/tilt mode retrieval. For the most demanding applications, a non-linear tip/tilt extraction method that self-consistently uses the speckle field may need to be developed.

关键词： wavefront sensing adaptive optics wavefront reconstruction algorithms

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Review on methods for wavefront reconstruction from pyramid wavefront sensor data

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JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS 2020年第1期6卷

作者： Shatokhina, Iuliia Hutterer, Victoria Ramlau, Ronny Johann Radon Inst Computat & Appl Math Linz Austria Johannes Kepler Univ Linz Ind Math Inst Linz Austria

Pyramid wavefront sensors are planned to be a part of many instruments that are currently under development for the extremely large telescopes (ELT). The unprecedented scales of the upcoming ELT-era instruments are inevitably connected with serious challenges for wavefront reconstruction and control algorithms. Apart from the huge number of correcting elements to be controlled in real-time, real-life features such as the segmentation of the telescope pupil, the low wind effect, the nonlinearity of the pyramid sensor, and the noncommon path aberrations will have a significantly larger impact on the imaging quality in the ELT framework than they ever had before. We summarize various kinds of wavefront reconstruction algorithms for the pyramid wavefront sensor. Based on several forward models, different algorithms were developed in the last decades for linear and nonlinear wavefront correction. The core ideas of the algorithms are presented, and a detailed comparison of the presented methods with respect to underlying pyramid sensor models, computational complexities, and reconstruction qualities is given. In addition, we review the existing and possible solutions for the above-named real-life phenomena. At the same time, directions for further investigations are sketched. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： adaptive optics pyramid wavefront sensor wavefront reconstruction algorithms island effect low wind effect optical gain nonlinearity noncommon path aberrations

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Spatial frequency response and sensitivity of the nonlinear curvature wavefront sensor 8

Spatial frequency response and sensitivity of the nonlinear ...

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Conference on Adaptive Optics Systems VIII Part of SPIE Astronomical Telescopes and Instrumentation Conference

作者： Letcheva, Stanimir Crassa, Jonathan Creppa, Justin R. Potier, Sam Univ Notre Dame Dept Phys & Astron 225 Nieuwland Sci Hall Notre Dame IN 46556 USA

ISBN: (纸本)9781510653528;9781510653511

The nonlinear curvature wavefront sensor (nlCWFS) has been shown to be a promising alternative to existing wavefront sensor designs. Theoretical studies indicate that the inherent sensitivity of this device could offer up to a factor of 10x improvement compared to the widely-used Shack-Hartmann wavefront sensor (SHWFS). The nominal nlCWFS design assumes the use of four detector measurement planes in a symmetric configuration centered around an optical system pupil plane. However, the exact arrangement of these planes can potentially be optimized to improve aberration sensitivity, and minimize the number of iterations involved in the wavefront reconstruction process, and therefore reduce latency. We present a systematic exploration of the parameter space for optimizing the nlCWFS design. Using a suite of simulation tools, we study the effects of measurement plane position on the performance of the nlCWFS and detector pixel sampling. A variety of seeing conditions are explored, assuming Kolmogorov turbulence. Results are presented in terms of residual wavefront error following reconstruction as well as the number of iterations required for solution convergence. Alternative designs to the symmetric four-plane design are studied, including three-plane and five-plane configurations. Finally, we perform a preliminary investigation of the effects of broadband illumination on sensor performance relevant to astronomy and other applications.

关键词： wavefront sensing adaptive optics wavefront reconstruction algorithms

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Advanced wavefront reconstruction methods for segmented Extremely Large Telescope pupils using pyramid sensors

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JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS 2018年第4期4卷

作者： Hutterer, Victoria Shatokhina, Iuliia Obereder, Andreas Ramlau, Ronny Johannes Kepler Univ Linz Ind Math Inst Linz Austria Austrian Acad Sci Johann Radon Inst Computat & Appl Math Linz Linz Austria

The generation of Extremely Large Telescopes (ELTs) with mirror diameters up to 40 m has thick secondary mirror support structures (also known as spider legs), which cause difficulties in the wavefront reconstruction process. These spider legs create areas where the information of the phase is disconnected on the wavefront sensor detector, leading to pupil fragmentation and a loss of data on selected subapertures. The effects on wavefront reconstruction are differential pistons between segmented areas, leading to poor wavefront reconstruction. The resulting errors make the majority of existing control algorithms unfeasible for telescope systems having spider legs incorporated. A solution, named the split approach, is presented, which suggests to separate reconstruction of segment piston modes from the rest of the wavefront. Further, two methods are introduced for the direct reconstruction of the segment pistons. Due to the separate handling of the piston offsets on the segments, the split approach makes any of the existing phase reconstruction algorithms developed for non-segmented pupils suitable for wavefront control in the presence of telescope spiders. We present end-to-end simulation results showing accurate, stable, and extremely fast wavefront reconstruction for the first light instrument mid-infrared ELT imager and spectograph of the ELT that is currently under construction. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： pyramid wavefront sensor wavefront reconstruction algorithms adaptive optics telescope spiders segmented telescope pupils

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Update on the TMT Adaptive Optics Real Time Controller

Update on the TMT Adaptive Optics Real Time Controller

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Conference on Adaptive Optics Systems

作者： Boyer, C. Gilles, L. Ellerbroek, B. Herriot, G. Veran, J. P. TMT Observ Corp 2632 E Washington Blvd Pasadena CA 91124 USA Herzberg Inst Astrophys Victoria BC V9E 2E7 Canada

ISBN: (纸本)9780819472250

The Thirty Meter Telescope (TMT) will implement a first light facility Laser Guide Star Multi Conjugate Adaptive Optics System, NFIRAOS, which will feed three science instruments on the telescope Nasmyth platform. This system will include two deformable mirrors, six laser guide star wavefront sensors, and multiple tip/tilt/focus wavefront sensors located in the instruments. The Real Time Controller (RTC) is one of the most innovative and essential components of this first light AO system. In this paper, we provide an update on the NFIRAOS RTC overall requirements and challenges, and in particular, on the tomography and fitting wavefront reconstruction algorithms. Several implementations of a minimum variance reconstructor are presented together with their processing and memory requirements.

关键词： Thirty Meter Telescope Adaptive Optics NFIRAOS Real Time Controller wavefront reconstruction algorithms

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