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1. 2022 upgrade and improved low frequency camera sensitivity for CMB observation at the South Pole

   https://doi.org/10.1117/12.2628058  

   Soliman, Ahmed; Ade, P.A.R.; Ahmed, Z.; Amiri, M.; Barkats, D.; Basu Thakur, R.; Bischoff, C.A.; Beck, D.; Bock, J.J.; Buza, V.; et al (August 2022, Proceedings of the SPIE)

   Zmuidzinas, Jonas; Gao, Jian-Rong (Ed.)

   Constraining the Galactic foregrounds with multi-frequency Cosmic Microwave Background (CMB) observations is an essential step towards ultimately reaching the sensitivity to measure primordial gravitational waves (PGWs), the sign of inflation after the Big-Bang that would be imprinted on the CMB. The BICEP Array is a set of multi-frequency cameras designed to constrain the energy scale of inflation through CMB B-mode searches while also controlling the polarized galactic foregrounds. The lowest frequency BICEP Array receiver (BA1) has been observing from the South Pole since 2020 and provides 30 GHz and 40 GHz data to characterize galactic synchrotron in our CMB maps. In this paper, we present the design of the BA1 detectors and the full optical characterization of the camera including the on-sky performance at the South Pole. The paper also introduces the design challenges during the first observing season including the effect of out-of-band photons on detectors performance. It also describes the tests done to diagnose that effect and the new upgrade to minimize these photons, as well as installing more dichroic detectors during the 2022 deployment season to improve the BA1 sensitivity. We finally report background noise measurements of the detectors with the goal of having photon-noise dominated detectors in both optical channels. BA1 achieves an improvement in mapping speed compared to the previous deployment season. 

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2. Active control of laser beam pointing for the Zettawatt-Equivalent Ultrashort pulse laser System: a proof-of-principle study with 16-inch optics

   https://doi.org/10.1017/hpl.2025.10064  

   Huang, Hao; Nutting, Tanner; McKelvey, Andrew; Hou, Bixue; Burger, Miloš; Ma, Yong; Weinberg, Lauren; Kalinchenko, Galina; Maksimchuk, Anatoly; Nees, John; et al (January 2025, High Power Laser Science and Engineering)

   Abstract We present a proof-of-principle study of active beam-pointing control for the Zettawatt-Equivalent Ultrashort pulse laser System (ZEUS) using a piezo-actuated 16-inch mirror. To the best of our knowledge, this is the largest actively controlled mirror reported in a high-power laser system. A simple proportional feedback control was implemented based on a field-programmable gate array, which reduced the standard deviation of beam-pointing fluctuations by 91% to 0.075 μrad in the horizontal direction and by 78% to 0.25 μrad in the vertical direction. We also demonstrated the elimination of long-term pointing jitter caused by temperature drift using the same apparatus. 

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3. Design of the SPT-SLIM Focal Plane: A Spectroscopic Imaging Array for the South Pole Telescope

   https://doi.org/10.1007/s10909-022-02843-4  

   Barry, P. S.; Anderson, A.; Benson, B.; Carlstrom, J. E.; Cecil, T.; Chang, C.; Dobbs, M.; Hollister, M.; Karkare, K. S.; Keating, G. K.; et al (December 2022, Journal of Low Temperature Physics)

   Abstract The Summertime Line Intensity Mapper (SLIM) is a mm-wave line-intensity mapping (mm-LIM) experiment for the South Pole Telescope (SPT). The goal of SPT-SLIM is to serve as a technical and scientific pathfinder for the demonstration of the suitability and in-field performance of multi-pixel superconducting filterbank spectrometers for future mm-LIM experiments. Scheduled to deploy in the 2023-24 austral summer, the SPT-SLIM focal plane will include 18 dual-polarisation pixels, each coupled to an $$R = \lambda / \Delta \lambda = 300$$ R = λ / Δ λ = 300 thin-film microstrip filterbank spectrometer that spans the 2 mm atmospheric window (120–180 GHz). Each individual spectral channel feeds a microstrip-coupled lumped-element kinetic inductance detector, which provides the highly multiplexed readout for the 10k detectors needed for SPT-SLIM. Here, we present an overview of the preliminary design of key aspects of the SPT-SLIM focal plane array, a description of the detector architecture and predicted performance, and initial test results that will be used to inform the final design of the SPT-SLIM spectrometer array. 

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4. Low-cost Access to the Deep, High-cadence Sky: the Argus Optical Array

   https://doi.org/10.1088/1538-3873/ac4811  

   Law, Nicholas M.; Corbett, Hank; Galliher, Nathan W.; Gonzalez, Ramses; Vasquez, Alan; Walters, Glenn; Machia, Lawrence; Ratzloff, Jeff; Ackley, Kendall; Bizon, Chris; et al (March 2022, Publications of the Astronomical Society of the Pacific)

   Abstract New mass-produced, wide-field, small-aperture telescopes have the potential to revolutionize ground-based astronomy by greatly reducing the cost of collecting area. In this paper, we introduce a new class of large telescope based on these advances: an all-sky, arcsecond-resolution, 1000 telescope array which builds a simultaneously high-cadence and deep survey by observing the entire sky all night. As a concrete example, we describe the Argus Array, a 5 m-class telescope with an all-sky field of view and the ability to reach extremely high cadences using low-noise CMOS detectors. Each 55 GPix Argus exposure covers 20% of the entire sky to m g = 19.6 each minute and m g = 21.9 each hour; a high-speed mode will allow sub-second survey cadences for short times. Deep coadds will reach m g = 23.6 every five nights over 47% of the sky; a larger-aperture array telescope, with an étendue close to the Rubin Observatory, could reach m g = 24.3 in five nights. These arrays can build two-color, million-epoch movies of the sky, enabling sensitive and rapid searches for high-speed transients, fast-radio-burst counterparts, gravitational-wave counterparts, exoplanet microlensing events, occultations by distant solar system bodies, and myriad other phenomena. An array of O(1000) telescopes, however, would be one of the most complex astronomical instruments yet built. Standard arrays with hundreds of tracking mounts entail thousands of moving parts and exposed optics, and maintenance costs would rapidly outpace the mass-produced-hardware cost savings compared to a monolithic large telescope. We discuss how to greatly reduce operations costs by placing all optics in thermally controlled, sealed domes with only a few moving parts. Coupled with careful software scope control and use of existing pipelines, we show that the Argus Array could become the deepest and fastest Northern sky survey, with total costs in the $20M range. 

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5. Results and Limits of Time-Division Multiplexing for the BICEP Array High-Frequency Receivers

   https://doi.org/10.1007/s10909-024-03100-6  

   Fatigoni, S; Ade, P A_R; Ahmed, Z; Amiri, M; Barkats, D; Thakur, R Basu; Bischoff, C A; Beck, D; Bock, J J; Buza, V; et al (April 2024, Journal of Low Temperature Physics)

   Time-division multiplexing is the readout architecture of choice for many ground and space experiments, as it is a very mature technology with proven outstanding low-frequency noise stability, which represents a central challenge in multiplexing. Once fully populated, each of the two BICEP Array high-frequency receivers, observing at 150 GHz and 220/270 GHz, will have 7776 TES detectors tiled on the focal plane. The constraints set by these two receivers required a redesign of the warm readout electronics. The new version of the standard multichannel electronics, developed and built at the University of British Columbia, is presented here for the first time. BICEP Array operates time-division multiplexing readout technology to the limits of its capabilities in terms of multiplexing rate, noise and cross talk, and applies them in rigorously demanding scientific application requiring extreme noise performance and systematic error control. Future experiments like CMB-S4 plan to use TES bolometers with time-division/SQUID-based readout for an even larger number of detectors. 

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