The Hybrid Wavefront Sensor
The designs of a Shack-Hartmann (SHWFS) and unmodulated Pyramid Wavefront Sensor (PyWFS) lay the groundwork of the Hybrid Wavefront Sensor (HyWFS), which combines the components and strengths of both. Although both WFSs can exist separately on one bench, photon noise becomes the limiting factor when the light is split between two sensing arms and detectors. Instead, the HyWFS combines the optical components of a SHWFS and PyWFS into a single static system which produces two wavefront estimations from one image.
The optical design of the HyWFS is straightforward, using only two unique optics, a pyramid prism in the focal plane and lenslet array in the pupil plane. A typical SHWFS only measures the relative motion of spot images, while the PyWFS uses intensity maps to calculate wavefront error. Using both of these techniques with an unresolved source gives the HyWFS a unique advantage of producing two measurements for every single collected image. The final estimation is chosen strategically to yield a WFS which is highly sensitive and accurate over a large dynamic range. The layout of the HyWFS testbench is shown below.
The main advantage of the HyWFS lies in producing two wavefront estimations from a single image. Each estimation is based off typical reconstruction processes from a SHWFS and PyWFS. Both estimations require an adjustment to the HyWFS image to appear more like a conventional SHWFS or PyWFS image. By doing this, well established reconstruction and wavefront estimation techniques can be used for each mode. The final HyWFS estimation is chosen based on the overall Strehl ratio of the aberrated image.
Detailed testbench design of the HyWFS built at the University of Arizona Adaptive Optics Research Lab by Dr. Charlotte E. Guthery, Madison Jean, and Dr. Ryan Hamilton. Version 2of this design was rebuilt at the University of Arizona in the Large Optics Fabrication and Testing lab by Casey Scoggin and Oliver Wu.
To gain an understanding of the HyWFS response to varying strengths of turbulence, multiple simulated and bench tests have been conducted. Turbulence of the incident wavefront is constantly varying in amplitude and shape. The test shown to the right describes the strengths of the HyWFS's range, linearity, and sensitivity when used on-sky. The applied phase was scaled until the variance of the aberration was between 0.01 to 1 radian. Photon noise was present in the form of a magnitude 9.1 guide star, this value was not varied.
Results from these experiments follow the theory of the two mode response. The SHWFS mode minimizes the residual WFE present at high amplitudes of applied phase aberrations, above the PyWFS mode saturation point. Below this point, the residual WFE from the PyWFS mode correction averages an order of magnitude smaller. Switching between the modes yields a highly accurate wavefront estimation below the PyWFS mode saturation point, this will remain linear in the presence of large amplitudes of WFE.
Results from the simulated version of the Hybrid wavefront sensor, demonstrating the two reconstruction methods strengths and switching point.
Related Publications
Guthery et al., Single Mode Reconstruction Results with a Hybrid Wavefront Sensor Prototype, Optics Express, 2023 (pending)
Guthery, A Hybrid Wavefront Sensor for Wide-Range Adaptive Optics, Dissertation, 2022
Jean, Closed Loop Tip-Tilt Correction for a Pyramid-Shack-Hartmann Hybrid Wave-front Sensor, Master’s Thesis, 2021
Jean et al., Design and calibration of a closed loop tip-tilt control for a pyramid-Shack-Hartmann hybrid wave-front sensor, SPIE, 2021
Guthery and Hart, Pyramid and Shack-Hartmann hybrid wave-front sensor, Optics Letters, 2021
Guthery and Hart, Theory and Design of a Hybrid Wave-front Sensor for Adaptive Optics, AO4ELT6 & OSA, 2019
Hamilton et al., Designing, Building, and Testing of a Hybrid Wavefront Sensor for Adaptive Optics, AO4ELT6 & OSA, 2019
Team (Current)
Casey Scoggins, Ph.D. Student, University of Arizona
Oliver Wu, B.S. Student, University of Arizona
Prof. Daewook Kim, Advisor, University of Arizona
Dr. Charlotte E. Guthery, Advisor, W. M. Keck Observatory
Prof. Michael Hart, Advisor, Hart Scientific Consulting International
Dr. Lewis Roberts, SURP Advisor, NASA Jet Propulsion Laboratory
Dr. Kent Wallace, SURP Advisor, NASA Jet Propulsion Laboratory
Madison Jean, M.S. Student, Creative Micro Corporation
Rachel Turner, B.S. Student, University of Arizona
Dr. Justin Knight, Post-doc, Onto Innovation
Dr. Ryan Hamilton, Optical Engineer, RUDA Optical