Real-time control (RTC) is pivotal for any Adaptive Optics (AO) system, including high-contrast imaging of exoplanets and circumstellar environments. It is the brain of the AO system, and what wavefront sensing and control (WFS&C) techniques need to work with to achieve unprecedented image quality and contrast, ultimately advancing our understanding of exoplanetary systems in the context of high contrast imaging (HCI). Developing WFS&C algorithms first happens in simulation or a lab before deployment on-sky. The transition to on-sky testing is often challenging due to the different RTCs used. Sharing common RTC standards across labs and telescope instruments would considerably simplify this process. A data architecture based on the interprocess communication method known as shared memory is ideally suited for this purpose. The CACAO package, an example of RTC based on shared memory, was initially developed for the Subaru- SCExAO instrument and now deployed on several benches and instruments. This proceeding discusses the challenges, requirements, implementation strategies, and performance evaluations associated with integrating a shared memory-based RTC. The Santa Cruz Extreme AO Laboratory (SEAL) bench is a platform for WFS&C development for large groundbased segmented telescopes. Currently, SEAL offers the user a non-real-time version of CACAO, a shared-memory based RTC package initially developed for the Subaru-SCExAO instrument, and now deployed on several benches and instruments. We show here the example of the SEAL RTC upgrade as a precursor to both RTC upgrade at the 3-m Shane telescopes at Lick Observatory (Shane-AO) and a future development platform for the Keck II AO. This paper is aimed at specialists in AO, astronomers, and WFS&C scientists seeking a deeper introduction to the world of RTCs.
The most common instrument used by the exoplanet/brown dwarf direct imaging community at the W.M. Keck Observatory is currently the NIRC2 near-infrared imager. We document three on-sky testing results of non-uniform effects that exist in the NIRC2 system when operating in L and M-band that can affect the performance when conducting high-contrast imaging observations. First, we report the measurements of the throughput of the vector vortex L/M coronagraph. We quantify the throughput and additional background flux penalties, noting the effects of using the VVC in M-band are greater than in L-band. Second, we utilize the recently commissioned NIRC2 electronics upgrade to measure the L/M band sky variability at sub-second speeds. We find that the background varies at timescales of less than 30s, indicating that the electronics upgrade may improve opportunities for future surveys. Third, we document the contribution of the image derotator to the spatial non-uniformity in the background flux. We conclude by giving a set of how the Keck-NIRC2 high-contrast imaging community can adapt their observing strategies to improve the sensitivity of future surveys.
We performed closed-loop lab testing of large-format deformable mirrors (DMs) with hybrid variable reluctance actuators. TNO has been developing the hybrid variable reluctance actuators in support for a new generation of adaptive secondary mirrors (ASMs), which aim to be more robust and reliable. Compared to the voice coil actuators, this new actuator technology has a higher current to force efficiency, and thus can support DMs with thicker facesheets. Before putting this new technology on-sky, it is necessary to understand how to control it and how it behaves in closed-loop. We performed closed-loop tests with the Shack-Hartmann wavefront sensor with three large-format deformable mirrors that use the TNO actuators: DM3, FLASH, and IRTF-ASM-1 ASM. The wavefront sensor and the real-time control systems were developed for the NASA Infrared Telescope Facility (IRTF) and the UH 2.2-meter telescope ASMs. We tested IRTF-ASM-1 on-sky and proved that it meets all of our performance requirements. This work presents our lab setup for the experiments, the techniques we have employed to drive these new ASMs, the results of our closed-loop lab tests for FLASH and IRTF-ASM-1, and the on-sky closed-loop results of IRTF-ASM-1 ASM.
We are developing an adaptive secondary mirror (ASM) that uses a new actuator technology created by the Netherlands Organization for Applied Scientific Research (TNO). The TNO hybrid variable reluctance actuators have more than an order of magnitude better efficiency over the traditional voice coil actuators that have been used on existing ASMs and show potential for improving the long-term robustness and reliability of ASMs. To demonstrate the performance, operations, and serviceability of TNO’s actuators in an observatory, we have developed a 36-actuator prototype ASM for the NASA Infrared Telescope Facility (IRTF) called IRTF-ASM-1. IRTF-ASM-1 provides the first on-sky demonstration of this approach and will help us evaluate the long-term performance and use of this technology in an astronomical facility environment. We present calibration and performance results with the ASM in a Meniscus Hindle Sphere lens setup as well as preliminary on-sky results on IRTF. IRTF-ASM-1 achieved stable closed-loop performance on-sky with H-band Strehl ratios of 35-40% in long-exposure images under a variety of seeing conditions.
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.
As we enter the era of TESS and JWST, instrumentation that can carry out radial velocity measurements of exoplanet systems is in high demand. We will address this demand by upgrading the UC Lick Observatory’s 2.4-meter Automated Planet Finder (APF) telescope with an adaptive optics (AO) system. The AO upgrade will be directly integrated into the APF telescope by replacing the telescope’s static secondary mirror with a 61- actuator adaptive secondary mirror (ASM) to minimize the disturbance to the spectrograph optics. This upgrade is enabled by The Netherlands Organization for Applied Scientific Research’s (TNO) large-format deformable mirror technology, which is constructed using a new style of high-efficiency hybrid-variable reluctance actuator. We outline the technical design and manufacturing plan for the proposed APF AO upgrade and simulate the improvement to the science yield using HCIpy. Our simulations predict the AO upgrade will reduce the PSF instabilities due to atmospheric turbulence, concentrating the light on the spectrograph slit by a multiplicative factor of more than two (doubling the telescope’s observing efficiency) for targets as dim as I = 14. When completed, the APF adaptive secondary mirror will be among the first pairings of an ASM with a radial velocity spectrograph and become a pathfinder for similar AO systems in telescopes of all sizes.
We report on progress at the University of Hawaii on the integration and testing setups for the adaptive secondary mirror (ASM) for the University of Hawaii 2.2-meter telescope on Maunakea, Hawaii. We report on the development of the handling fixtures and alignment tools we will use along with progress on the optical metrology tools we will use for the lab and on-sky testing of the system.
We describe the current plans for developing an adaptive secondary mirror-based (ASM) adaptive optics (AO) system for WMKO. An ASM allows for the integration of AO into the telescope itself, broadening use of AO to include wide-field enhanced seeing, high contrast observations, and enabling future multi-conjugate upgrades. Such a system has the potential for enhancing a range of science objectives, improving the performance of both existing and future instrumentation at Keck. We describe a system level ASM-AO concept based on hybrid variable reluctance actuators, developed by TNO that simplifies the implementation of ASM’s.
Advancements in high-efficiency variable reluctance actuators are an enabling technology for building the next generation of large-format deformable mirrors, including adaptive secondary mirrors. The Netherlands Organization for Applied Scientific Research (TNO) has developed a new style of hybrid variable-reluctance actuator that requires approximately seventy-five times less power to operate as compared to the traditional style of voice-coil actuators. We present the initial performance results from laboratory testing of TNO's latest 19-actuator prototype mirror, FLASH. We report the linearity, hysteresis, natural shape flattening, actuator cross-coupling, creep, and repeatability of the FLASH prototype and compare the results to previous TNO prototype deformable mirrors. We also present results of the performance of FLASH on sub-millisecond timescales in order to estimate the limits for the use of this technology when utilized to perform high-contrast imaging adaptive optics.
Adaptive optics (AO) offers an opportunity to stabilize an image and maximize the spatial resolution achievable by ground based telescopes by removing the distortions due to the atmosphere. Typically, the deformable mirror in an AO system is integrated into the optical path between the secondary mirror and science instrument; in some cases, the deformable mirror is integrated into the telescope itself as an adaptive secondary mirror. However including the deformable mirror as the primary mirror of the telescope has been left largely unexplored due to the previous cost and complexity of large-format deformable mirror technology. In recent years this technology has improved, leaving deformable primary mirrors as a viable avenue towards higher actuator density and a simplification in testing and deploying adaptive optics systems. We present a case study to explore the benefits and trade-offs of integrating an adaptive optics system using the primary mirror of the telescope in small-to-mid-sized telescopes.
An Adaptive secondary mirror (ASM) allows for the integration of adaptive optics (AO) into the telescope itself. Adaptive secondary mirrors, based on hybrid variable reluctance (HVR) actuator technology, developed by TNO, provide a promising path to telescope-integrated AO. HVR actuators have the advantage of allowing mirrors that are sti↵er, more power ecient, and potentially less complex than similar, voice-coil based ASM’s. We are exploring the application of this technology via a laboratory testbed that will validate the technical approach. In parallel, we are developing conceptual designs for ASMs at several telescopes including the Automated Planet Finder Telescope (APF) and for Keck Observatory. An ASM for APF has the potential to double the light through the slit for radial velocity measurements, and dramatically improved the image stability. An ASM for WMKO enables ground layer AO correction and lower background infrared AO observations, and provides for more flexible deployment of instruments via the ability to adjust the location of the Cassegrain focus.
Advancements in making high-efficiency actuators are an enabling technology for building the next generation of large-format deformable mirrors. The Netherlands Organization for Applied Scientific Research (TNO) has developed a new style of variable-reluctance actuator that requires approximately eighty times less power to operate as compared to the traditional style of voice-coil actuators. We present the performance results from laboratory testing of TNO's 57-actuator large-format deformable mirror from measuring the influence functions, linearity, hysteresis, natural shape flattening, actuator cross-coupling, creep, repeatability, and actuator lifetime. We measure a linearity of 99.4 ± 0.33% and hysteresis of 2.10 ± 0.23% over a stroke of 10 microns, indicating that this technology has strong potential for use in on-sky adaptive secondary mirrors (ASMs). We summarize plans for future lab prototypes and ASMs that will further demonstrate this technology.
BICEP Array is a degree-scale Cosmic Microwave Background (CMB) experiment that will search for primordial B-mode polarization while constraining Galactic foregrounds. BICEP Array will be comprised of four receivers to cover a broad frequency range with channels at 30/40, 95, 150 and 220/270 GHz. The first low-frequency receiver will map synchrotron emission at 30 and 40 GHz and will deploy to the South Pole at the end of 2019. In this paper, we give an overview of the BICEP Array science and instrument, with a focus on the detector module. We designed corrugations in the metal frame of the module to suppress unwanted interactions with the antenna-coupled detectors that would otherwise deform the beams of edge pixels. This design reduces the residual beam systematics and temperature-to-polarization leakage due to beam steering and shape mismatch between polarized beam pairs. We report on the simulated performance of single- and wide-band corrugations designed to minimize these effects. Our optimized design alleviates beam differential ellipticity caused by the metal frame to about 7% over 57% bandwidth (25 to 45 GHz), which is close to the level due the bare antenna itself without a metal frame. Initial laboratory measurements are also presented.
BICEP3 is a 520mm aperture on-axis refracting telescope observing the polarization of the cosmic microwave background (CMB) at 95GHz in search of the B-mode signal originating from in ationary gravitational waves. BICEP3's focal plane is populated with modularized tiles of antenna-coupled transition edge sensor (TES) bolometers. BICEP3 was deployed to the South Pole during 2014-15 austral summer and has been operational since. During the 2016-17 austral summer, we implemented changes to optical elements that lead to better noise performance. We discuss this upgrade and show the performance of BICEP3 at its full mapping speed from the 2017 and 2018 observing seasons. BICEP3 achieves an order-of-magnitude improvement in mapping speed compared to a Keck 95GHz receiver. We demonstrate 6.6μK√s noise performance of the BICEP3 receiver.
The compelling science case for the observation of B-mode polarization in the cosmic microwave background (CMB) is driving the CMB community to expand the observed sky fraction, either by extending survey sizes or by deploying receivers to potential new northern sites. For ground-based CMB instruments, poorly-mixed atmospheric water vapor constitutes the primary source of short-term sky noise. This results in short-timescale brightness fluctuations, which must be rejected by some form of modulation. To maximize the sensitivity of ground-based CMB observations, it is useful to understand the effects of atmospheric water vapor over timescales and angular scales relevant for CMB polarization measurements. To this end, we have undertaken a campaign to perform a coordinated characterization of current and potential future observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far, we have deployed two identical WVR units; one at South Pole, Antarctica, and the other at Summit Station, Greenland. The former site has a long heritage of ground based CMB observations and is the current location of the Bicep/Keck Array telescopes and the South Pole Telescope. The latter site, though less well characterized, is under consideration as a northern-hemisphere location for future CMB receivers. Data collection from this campaign began in January 2016 at South Pole and July 2016 at Summit Station. Data analysis is ongoing to reduce the data to a single spatial and temporal statistic that can be used for one-to-one site comparison.
Bicep Array is a cosmic microwave background (CMB) polarization experiment that will begin observing at the South Pole in early 2019. This experiment replaces the five Bicep2 style receivers that compose the Keck Array with four larger Bicep3 style receivers observing at six frequencies from 30 to 270GHz. The 95GHz and 150GHz receivers will continue to push the already deep Bicep/Keck CMB maps while the 30/40GHz and 220/270GHz receivers will constrain the synchrotron and galactic dust foregrounds respectively. Here we report on the design and performance of the Bicep Array instruments focusing on the mount and cryostat systems.
Targeting faint polarization patterns arising from Primordial Gravitational Waves in the Cosmic Microwave Background requires excellent observational sensitivity. Optical elements in small aperture experiments such as Bicep3 and Keck Array are designed to optimize throughput and minimize losses from transmission, reflection and scattering at millimeter wavelengths. As aperture size increases, cryostat vacuum windows must withstand larger forces from atmospheric pressure and the solution has often led to a thicker window at the expense of larger transmission loss. We have identified a new candidate material for the fabrication of vacuum windows: with a tensile strength two orders of magnitude larger than previously used materials, woven high-modulus polyethylene could allow for dramatically thinner windows, and therefore significantly reduced losses and higher sensitivity. In these proceedings we investigate the suitability of high-modulus polyethylene windows for ground-based CMB experiments, such as current and future receivers in the Bicep/Keck Array program. This includes characterizing their optical transmission as well as their mechanical behavior under atmospheric pressure. We find that such ultra-thin materials are promising candidates to improve the performance of large-aperture instruments at millimeter wavelengths, and outline a plan for further tests ahead of a possible upcoming field deployment of such a science-grade window.
Bicep Array is the newest multi-frequency instrument in the Bicep/Keck Array program. It is comprised of four 550mm aperture refractive telescopes observing the polarization of the cosmic microwave background (CMB) at 30/40, 95, 150 and 220/270 GHz with over 30,000 detectors. We present an overview of the receiver, detailing the optics, thermal, mechanical, and magnetic shielding design. Bicep Array follows Bicep3's modular focal plane concept, and upgrades to 6" wafer to reduce fabrication with higher detector count per module. The first receiver at 30/40GHz is expected to start observing at the South Pole during the 2019-20 season. By the end of the planned Bicep Array program, we project 0.002 ⪅ σ(r) ⪅ 0.006, assuming current modeling of polarized Galactic foreground and depending on the level of delensing that can be achieved with higher resolution maps from the South Pole Telescope.
H. Hui, P. Ade, Z. Ahmed, K. Alexander, M. Amiri, D. Barkats, S. Benton, C. Bischoff, J. Bock, H. Boenish, R. Bowens-Rubin, I. Buder, E. Bullock, V. Buza, J. Connors, J. Filippini, S. Fliescher, J. Grayson, M. Halpern, S. Harrison, G. Hilton, V. Hristov, K. Irwin, J. Kang, K. Karkare, E. Karpel, S. Kefeli, S. Kernasovskiy, J. Kovac, C. L. Kuo, E. Leitch, M. Lueker, K. Megerian, V. Monticue, T. Namikawa, C. Netterfield, H. Nguyen, R. O'Brient, R. Ogburn, C. Pryke, C. Reintsema, S. Richter, R. Schwarz, C. Sorensen, C. Sheehy, Z. Staniszewski, B. Steinbach, G. Teply, K. Thompson, J. Tolan, C. Tucker, A. Turner, A. Vieregg, A. Wandui, A. Weber, D. Wiebe, J. Willmert, W. L. Wu, K. W. Yoon
BICEP3, the latest telescope in the BICEP/Keck program, started science observations in March 2016. It is a 550mm aperture refractive telescope observing the polarization of the cosmic microwave background at 95 GHz. We show the focal plane design and detector performance, including spectral response, optical efficiency and preliminary sensitivity of the upgraded BICEP3. We demonstrate 9.72 μKCMB√s noise performance of the BICEP3 receiver.
K. Karkare, P. A. Ade, Z. Ahmed, K. Alexander, M. Amiri, D. Barkats, S. Benton, C. Bischoff, J. Bock, H. Boenish, R. Bowens-Rubin, I. Buder, E. Bullock, V. Buza, J. Connors, J. Filippini, S. Fliescher, J. Grayson, M. Halpern, S. Harrison, G. Hilton, V. Hristov, H. Hui, K. Irwin, J. Kang, E. Karpel, S. Kefeli, S. Kernasovskiy, J. Kovac, C. L. Kuo, E. Leitch, M. Lueker, K. Megerian, V. Monticue, T. Namikawa, C. Netterfield, H. T. Nguyen, R. O'Brient, R. Ogburn, C. Pryke, C. Reintsema, S. Richter, M. St. Germaine, R. Schwarz, C. Sheehy, Z. Staniszewski, B. Steinbach, G. Teply, K. Thompson, J. Tolan, C. Tucker, A. Turner, A. Vieregg, A. Wandui, A. Weber, J. Willmert, C. L. Wong, W. L. Wu, K. W. Yoon
BICEP3 is a small-aperture refracting cosmic microwave background (CMB) telescope designed to make sensitive polarization maps in pursuit of a potential B-mode signal from inflationary gravitational waves. It is the latest in the Bicep/Keck Array series of CMB experiments located at the South Pole, which has provided the most stringent constraints on inflation to date. For the 2016 observing season, BICEP3 was outfitted with a full suite of 2400 optically coupled detectors operating at 95 GHz. In these proceedings we report on the far field beam performance using calibration data taken during the 2015-2016 summer deployment season in situ with a thermal chopped source. We generate high-fidelity per-detector beam maps, show the array-averaged beam profile, and characterize the differential beam response between co-located, orthogonally polarized detectors which contributes to the leading instrumental systematic in pair differencing experiments. We find that the levels of differential pointing, beamwidth, and ellipticity are similar to or lower than those measured for Bicep2 and Keck Array. The magnitude and distribution of Bicep3’s differential beam mismatch – and the level to which temperature-to-polarization leakage may be marginalized over or subtracted in analysis - will inform the design of next-generation CMB experiments with many thousands of detectors.
J. Grayson, P. A. Ade, Z. Ahmed, K. Alexander, M. Amiri, D. Barkats, S. Benton, C. Bischoff, J. Bock, H. Boenish, R. Bowens-Rubin, I. Buder, E. Bullock, V. Buza, J. Connors, J. Filippini, S. Fliescher, M. Halpern, S. Harrison, G. Hilton, V. Hristov, H. Hui, K. Irwin, J. Kang, K. Karkare, E. Karpel, S. Kefeli, S. Kernasovskiy, J. Kovac, C. L. Kuo, E. Leitch, M. Lueker, K. Megerian, V. Monticue, T. Namikawa, C. Netterfield, H. Nguyen, R. O'Brient, R. Ogburn, C. Pryke, C. Reintsema, S. Richter, R. Schwarz, C. Sorenson, C. Sheehy, Z. Staniszewski, B. Steinbach, G. Teply, K. Thompson, J. Tolan, C. Tucker, A. Turner, A. Vieregg, A. Wandui, A. Weber, D. Wiebe, J. Willmert, W. L. Wu, K. W. Yoon
Bicep3 is a 520mm aperture, compact two-lens refractor designed to observe the polarization of the cosmic microwave background (CMB) at 95 GHz. Its focal plane consists of modularized tiles of antenna-coupled transition edge sensors (TESs), similar to those used in Bicep2 and the Keck Array. The increased per-receiver optical throughput compared to Bicep2/Keck Array, due to both its faster f=1:7 optics and the larger aperture, more than doubles the combined mapping speed of the Bicep/Keck program. The Bicep3 receiver was recently upgraded to a full complement of 20 tiles of detectors (2560 TESs) and is now beginning its second year of observation (and first science season) at the South Pole. We report on its current performance and observing plans. Given its high per-receiver throughput while maintaining the advantages of a compact design, Bicep3- class receivers are ideally suited as building blocks for a 3rd-generation CMB experiment, consisting of multiple receivers spanning 35 GHz to 270 GHz with total detector count in the tens of thousands. We present plans for such an array, the new "BICEP Array" that will replace the Keck Array at the South Pole, including design optimization, frequency coverage, and deployment/observing strategies.
Bicep3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of Bicep1, Bicep2 and the Keck Array experiments | it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, Bicep3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5x larger than a Bicep2/Keck Array receiver and faster optics (f=1:6 vs. f=2:4). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, Bicep3 will have survey speed comparable to Keck Array 150 GHz (2013), and will signifcantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the Bicep2 observation patch
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