One of the major contributors to residual wavefront error for the Adaptive Optics (AO) systems at W. M. Keck Observatory is considered a high order wavefront error. This term accounts for multiple sources including primary mirror segment errors, non-common path aberrations, and more. Fast and Furious (F&F) is a focal plane wavefront sensing algorithm offered as an observation tool to correct these errors. F&F uses a science image and the previous AO correction to measure errors with no diversity frames needed. In practice F&F showed consistent improvement of the Strehl ratio throughout an observing night, with a maximum improvement of 20%. The current observational tool is operational with a single science instrument (NIRC2) and AO with a natural guide star, with upgrades to all AO-fed instruments on the way. This tool can be operated by observers and can be used for monitoring any degradation in AO performance on-sky.
The Zernike wavefront sensor (ZWFS) stands out as one of the most sensitive optical systems for measuring the phase of an incoming wavefront, reaching photon efficiencies close to the fundamental limit. This quality, combined with the fact that it can easily measure phase discontinuities, has led to its widespread adoption in various wavefront control applications, both on the ground but also for future space-based instruments. Despite its advantages, the ZWFS faces a significant challenge due to its extremely limited dynamic range, making it particularly challenging for ground-based operations. To address this limitation, one approach is to use the ZWFS after a general adaptive optics (AO) system; however, even in this scenario, the dynamic range remains a concern. This paper investigates two optical configurations of the ZWFS: the conventional setup and its phase-shifted counterpart, which generates two distinct images of the telescope pupil. We assess the performance of various reconstruction techniques for both configurations, spanning from traditional linear reconstructors to gradient-descent-based methods. The evaluation encompasses simulations and experimental tests conducted on the Santa cruz Extreme Adaptive optics Lab (SEAL) bench at UCSC. Our findings demonstrate that certain innovative reconstruction techniques introduced in this study significantly enhance the dynamic range of the ZWFS, particularly when utilizing the phase-shifted version.
As part of the High order Advanced Keck Adaptive optics (HAKA) project, a state-of-the-art ALPAO 2844 actuator deformable mirror (DM) will replace the more than 25 years old 349 actuator DM on the Keck ⅠⅠ Adaptive Optics (AO) bench. The increase in the number of DM actuators requires a new set of pupil-relay optics (PRO) to map the 2.5mm DM actuator spacing to the 200μm lenslet spacing on the Shack-Hartmann wavefront sensor (WFS). A new lenslet array with increased focal lengths will be procured in order to maintain current plate scales. HAKA will initially support science with the near-infrared camera (NIRC2), a single mode fiber fed spectrograph (KPIC + NIRSPEC) and a fast visible imager (ORKID). In addition, a new infrared wavefront sensor (‘IWA) is being designed to support science with ORKID and a suite of new science instruments: a mid-infrared coronagraphic integral field spectrograph (SCALES) and a fiber-fed high-resolution spectrograph (HISPEC). We present the opto-mechanical design of the HAKA DM, Shack-Hartmann WFS upgrades and the ‘IWA system. A mount for the HAKA DM will allow for quick integration and alignment to the Keck ⅠⅠ AO bench. The upgrade to the WFS PRO includes a new set of optics and associated mounting that fits within the mechanical constraints of the existing WFS and meets the requirements of the HAKA DM.
We extend our previous demonstration of the first on-sky primary mirror segment closed-loop control on Keck using a vector-Zernike wavefront sensor (vZWFS), which improved the Strehl ratio on the NIRC2 science camera by up to 10 percentage points. Segment co-phasing errors contribute to Keck contrast limits and will be necessary to correct for the segmented Extremely Large Telescopes and future space missions. The goal of the post-AO vZWFS on Keck is to monitor and correct segment co-phasing errors in parallel with science observations. The ZWFS is ideal for measuring phase discontinuities and is one of the most sensitive WFSs, but has limited dynamic range. The Keck vZWFS consists of a metasurface mask imposing two different phase shifts to orthogonal polarizations, split into two pupil images, extending its dynamic range. We report on the vZWFS closed-loop co-phasing performance and early work towards understanding the interactions between the AO system and segment phasing. We discuss a comparison of the AO performance when co-phasing by aligning segment edges, as is currently done at Keck, compared with aligning to the average phase over the segments, as is done by the vZWFS.
The first scientific observations with adaptive optics (AO) at W. M. Keck Observatory (WMKO) began in 1999. Through 2023, over 1200 refereed science papers have been published using data from the WMKO AO systems. The scientific competitiveness of AO at WMKO has been maintained through a continuous series of AO and instrument upgrades and additions. This tradition continues with AO being a centerpiece of WMKO’s scientific strategic plan for 2035. We will provide an overview of the current and planned AO projects from the context of this strategic plan. The current projects include implementation of new real-time controllers, the KAPA laser tomography system and the HAKA high-order deformable mirror system, the development of multiple advanced wavefront sensing and control techniques, the ORCAS space-based guide star project, and three new AO science instruments. We will also summarize steps toward the future strategic directions which are centered on ground-layer, visible and high-contrast AO.
The Keck Planet Imager and Characterizer (KPIC) instrument at the Keck Observatory consists of a series of upgrades to the Keck II Adaptive Optics system and the NIRSPEC spectrograph to enable diffraction-limited, high-resolution (R∼35, 000) spectroscopy, originally in the K (∼2.0−2.5 μm) and L (∼3.2−3.7 μm) bands only. Phase I consisted of single-mode fiber injection/extraction units used in conjunction with an H band pyramid wavefront sensor. Using single-mode fibers provides a gain in stellar rejection, a substantial reduction in sky background, and a stable, well-defined line-spread function on the spectrograph. In 2022, Phase II brought a 1000-actuator deformable mirror, beam-shaping optics, a vortex fiber nulling mode, and more.
In this paper we present the results of the latest upgrades to the KPIC instrument. Among these upgrades, a second fiber bundle with related injection/extraction optics and new dichroics were added to extend KPIC’s science capabilities to y through H band, and to provide access to laser frequency combs for spectral calibration from y-K. Additionally, the charge 2 vortex mask for fiber nulling was supplemented with a charge 1 mask to enable spectroscopy of low mass companions at very small angular separations. Other upgrades included an atmospheric dispersion corrector, a new calibration source switching system, and an optimized tip/tilt control system. Here we show preliminary results of on-sky tests performed in the first few months of re-commissioning, along with the next steps for the instrument.
GPI2.0 is an upgrade of the high-contrast instrument known as the Gemini Planet Imager (GPI). This new version is scheduled for installation on Gemini North telescope by the end of 2024. In this document, we outline our approach for addressing Non-Common Path Aberrations (NCPA) measurement and correction within the instrument. Our strategy differs significantly from the methods employed in the original GPI. Our proposal involves the utilization of a dedicated Wavefront Sensor (WFS) positioned within the coronagraph branch to accurately measure NCPAs. Subsequently, we will compensate for these aberrations by transmitting offset signals to the adaptive optics WFS. The chosen dedicated WFS will be a Zernike WFS (ZWFS), known for its exceptional sensitivity. This paper provides insights into the integration plan for incorporating the ZWFS into GPI2.0, details its key characteristics, and outlines the methodology for performing phase inversion based on the ZWFS measurements. Additionally, we present the initial results of experimental tests conducted on the SEAL testbed at the University of California, Santa Cruz (UCSC).
The design of a CubeSat telescope for academic research purposes must balance complicated optical and structural designs with cost to maximize performance in extreme environments. Increasing the CubeSat size (eg. 6U to 12U) will increase the potential optical performance, but the cost will increase in kind. Recent developments in diamond-turning have increased the accessibility of aspheric aluminum mirrors, enabling a cost-effective regime of well-corrected nanosatellite telescopes. We present an all-aluminum versatile CubeSat telescope (VCT) platform that optimizes performance, cost, and schedule at a relatively large 95 mm aperture and 0.4 degree diffraction limited full field of view stablized by MEMS fine-steering modules. This study features a new design tool that permits easy characterization of performance degradation as a function of spacecraft thermal and structural disturbances. We will present details including the trade between on- and off-axis implementations of the VCT, thermal stability requirements and finite-element analysis, and launch survival considerations. The VCT is suitable for a range of CubeSat borne applications, which provides an affordable platform for astronomy, Earth-imaging, and optical communications.
The Hybrid Wave-front Sensor (HyWFS) has previously been developed as a combination of a Pyramid Wave-front Sensor (PyWFS) and a Shack-Hartmann Wave-front Sensor (SHWFS) to capture the desirable properties of each when operated with an unresolved guide beacon. A pyramid prism placed at a focus divides the beacon light into four beams. At a reimaged pupil, a lenslet array creates four separate spot patterns on a detector. The measured intensities may be analyzed both in the manner of a PyWFS and a SHWFS, generating two approximations of the wave front that together achieve the high sensitivity of the PyWFS and the high dynamic range of the SHWFS. Given its inherent sensitivity, calibrating the HyWFS is challenged by the effects of local vibrations and air currents in the laboratory. To overcome this problem, a prototype HyWFS has been built that features a closed loop tip-tilt control sub-system. The design includes additional pupil planes, a Fast Steering Mirror (FSM), and a tip-tilt sensor. The prototype HyWFS will be calibrated with low-order Zernike polynomials at a variety of amplitudes to confirm the sensor’s sensitivity, dynamic range, and the effectiveness of the tip-tilt control loop. The effect of the tip-tilt loop will be quantified by comparing calibration qualities while the loop is active and inactive. The residual wave-front error is anticipated to decrease with active tip-tilt control in both the PyWFS mode and the SHWFS mode. With improved accuracy, the HyWFS is another step closer to on sky operation in a closed loop adaptive optics system.
Recent advances in pointing and tracking capabilities of small satellite platforms have enabled adoption of capabilities such as high-resolution Earth Observation (EO), inter-satellite laser communications and, more recently, quantum communications. Quantum communications requires unusually narrow optical beams and tight pointing performance (on the order of ten microradians) to close an inherently brightness-limited quantum link. This limit is due to quantum communication protocols such as quantum key distribution and teleportation requiring individual quantum states to be transmitted with photon number restrictions. We examine an opportunity to combine quantum communications with laser communications in sharing an optical link. We discuss a combined quantum and laser communication terminal capable of performing space-to-ground entanglement-distribution and high data rate communications on a 12U CubeSat with a 95mm beam expander and an 60 cm aperture optical ground telescope. Photon pairs produced by the quantum terminal are entangled in polarization so the polarization must be maintained throughout the optical link. We discuss active and passive compensation methods in space and polarization reference frame correction using a polarized reference beacon at the ground station. The combined quantum and laser communication terminal approach enables secure communications over an optical channel with rates of 100 Mbps and sub-nanosecond time transfer.
The Coronagraphic Debris Exoplanet Exploring Payload (CDEEP) is a Small-Sat mission concept for high contrast imaging of circumstellar disks. CDEEP is designed to observe disks in scattered light at visible wavelengths at a raw contrast level of 10-7 per resolution element (10-8 with post processing). This exceptional sensitivity will allow the imaging of transport dominated debris disks, quantifying the albedo, composition, and morphology of these low-surface brightness disks. CDEEP combines an off-axis telescope, microelectromechanical systems (MEMS) deformable mirror, and a vector vortex coronagraph (VVC). This system will require rigorous testing and characterization in a space environment. We report on the CDEEP mission concept, and the status of the vacuum-compatible CDEEP prototype testbed currently under development at the University of Arizona, including design development and the results of simulations to estimate performance.
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