63 research outputs found
Monolithic Kilopixel Silicon Microlens Arrays for Future Far-Infrared Observatories
No full textFuture far-infrared astrophysics observatories will require focal plane
arrays containing thousands of ultra-sensitive, superconducting detectors, each
of which needs to be optically coupled to the telescope. At longer wavelengths,
many approaches have been developed including feedhorn arrays and macroscopic
arrays of lenslets. However, with wavelengths as short as 25 microns, optical
coupling in the far-infrared remains challenging. In this paper, we present a
novel approach for fabricating far-infrared monolithic silicon microlens arrays
using grayscale lithography and deep reactive ion etching. The design,
fabrication, and characterization of the microlens arrays are discussed. We
compare the designed and fabricated lens profile, and calculate that the
fabricated lenses will achieve 84% encircled power for the designed detector,
which is only 3% less than the designed performance. We also present methods
developed for anti-reflection coating microlens arrays and for a
silicon-to-silicon die bonding process to hybridize microlens arrays with
detector arrays
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Readout of two-kilopixel transition-edge sensor arrays for Advanced ACTPol
No full textAdvanced ACTPol is an instrument upgrade for the six-meter Atacama Cosmology Telescope (ACT) designed to measure the cosmic microwave background (CMB) temperature and polarization with arcminute-scale angular resolution. To achieve its science goals, Advanced ACTPol utilizes a larger readout multiplexing factor than any previous CMB experiment to measure detector arrays with approximately two thousand transition-edge sensor (TES) bolometers in each 150 mm detector wafer. We present the implementation and testing of the Advanced ACTPol time-division multiplexing readout architecture with a 64-row multiplexing factor. This includes testing of individual multichroic detector pixels and superconducting quantum interference device (SQUID) multiplexing chips as well as testing and optimizing of the integrated readout electronics. In particular, we describe the new automated multiplexing SQUID tuning procedure developed to select and optimize the thousands of SQUID parameters required to readout each Advanced ACTPol array. The multichroic detector pixels in each array use separate channels for each polarization and each of the two frequencies, such that four TESes must be read out per pixel. Challenges addressed include doubling the number of detectors per multiplexed readout channel compared to ACTPol and optimizing the Nyquist inductance to minimize detector and SQUID noise aliasing
Highly Uniform 150 mm Diameter Multichroic Polarimeter Array Deployed for CMB Detection
No full textThe Advanced Atacama Cosmology Telescope Polarimeter is an upgraded receiver for the Atacama Cosmology Telescope, which has begun making measurements of the small angular scale polarization anisotropies in the Cosmic Microwave Background using the first of four new multichroic superconducting detector arrays. Here, we review all details of the optimization and characterization of this first array, which features 2012 AlMn transition edge sensor bolometers operating at 150 and 230 GHz. We present critical temperatures, thermal conductivities,saturation powers, time constants, and sensitivities for the array. The results show high uniformity across the 150 mm wafer and good performance in the field
Metal-Mesh Linear Variable Filter for Far-Infrared Wavelengths
No full textFuture far-infrared (IR) observatories require compact and cost efficient optical linear variable bandpass filters (LVBFs) to define their instrument spectral bands. We have designed novel far-IR LVBFs that consist of metal-mesh bandpass filters comprised of a gold film with cross-slots of varying sizes along a silicon (Si) substrate with anti-reflection (AR) coatings. We present our work on the simulated and measured transmission of non-AR coated and AR coated LVBFs for bandpass peaks from wavelengths of 24 to 36 m with a resolving power () of R6 for non-AR coated LVBFs and R4 for AR coated LVBFs. We also present a method to decrease the effects of out-of-band high frequency transmission exhibited by metal-mesh filters by depositing a thin layer of hydrogenated amorphous silicon (a-Si:H) on the metal-mesh of the LVBF. We have fabricated and measured the LVBFs at room temperature and cryogenic temperatures (5 K). We measure a high peak transmission of 80-90 \% for the AR coated LVBF at 5 K and demonstrate that the a-Si:H LVBF is a promising method to address out-of-band high frequency transmission.8 pages, 10 figures, accepted to Applied Optic
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Simons Observatory HoloSim-ML : machine learning applied to the efficient analysis of radio holography measurements of complex optical systems
No full textNear-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter and sub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holography measurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Python code for beam simulation and analysis of radio holography data from complex optical systems. This code uses machine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with few micrometer accuracy. We apply this approach to the example of the Simons Observatory 6 m telescope.</p
Characterization of a Far-Infrared Kinetic Inductance Detector Prototype for PRIMA
No full textThe PRobe far-Infrared Mission for Astrophysics (PRIMA) is under study as a
potential far-IR space mission, featuring actively cooled optics, and both
imaging and spectroscopic instrumentation. To fully take advantage of the low
background afforded by a cold telescope, spectroscopy with PRIMA requires
detectors with a noise equivalent power (NEP) better than W
Hz. To meet this goal we are developing large format arrays of kinetic
inductance detectors (KIDs) to work across the micron range. Here we
present the design and characterization of a single pixel prototype detector
optimized for micron. The KID consists of a lens-coupled aluminum
inductor-absorber connected to a niobium interdigitated capacitor to form a 2
GHz resonator. We have fabricated a small array with 28 KIDs, and we measure
the performance of one of these detectors with an optical loading in the aW range. At low loading the detector achieves an NEP of
W Hz at a 10 Hz readout frequency, and the
lens-absorber system achieves a good optical efficiency. An extrapolation of
these measurements suggest this detector may remain photon noise limited at up
to 20 fW of loading, offering a high dynamic range for PRIMA observations of
bright astronomical sources.Comment: revised submission to IEEE Transactions on Terahertz Science and
Technolog
Development of an optical detector testbed for the Simons Observatory
No full textThe Simons Observatory (SO) is a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field over 60,000 transition edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities, as outlined in The Simons Observatory Collaboration et al. (2019). To verify consistency of fabrication and performance in line with our sensitivity requirements, we will perform in-lab optical tests on isolated SO detectors as well as full detector arrays. The tests include beam measurements, bandpass measurements, and polarization measurements, among others. Here, we will describe the development of a cryogenic testbed that enables optical characterization of SO's detectors. We include the infrared filtering strategy to allow suitable cryogenic performance, design and implementation of the test equipment used in characterization, and the preliminary results from our validation of the testbed's cryo-optical performance...
Studies of Systematic Uncertainties for Simons Observatory: Optical Effects and Sensitivity Considerations
No full textInternational audienceThe Simons Observatory (SO) is a new experiment that aims to measure the cosmic microwave background (CMB) in temperature and polarization. SO will measure the polarized sky over a large range of microwave frequencies and angular scales using a combination of small () and large () aperture telescopes and will be located in the Atacama Desert in Chile. This work is part of a series of papers studying calibration, sensitivity, and systematic errors for SO. In this paper, we discuss current efforts to model optical systematic effects, how these have been used to guide the design of the SO instrument, and how these studies can be used to inform instrument design of future experiments like CMB-S4. While optical systematics studies are underway for both the small aperture and large aperture telescopes, we limit the focus of this paper to the more mature large aperture telescope design for which our studies include: pointing errors, optical distortions, beam ellipticity, cross-polar response, instrumental polarization rotation and various forms of sidelobe pickup
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