The Mexico-UK Submillimeter Camera for AsTronomy (MUSCAT) is a continuum camera in the 1.1-mm band for the Large Millimeter Telescope (LMT), with 1458 lumped-element kinetic inductance detectors distributed across six arrays. Installed on the telescope at the end of 2021, we present the characterization of the detector beams of four of the six arrays based on the beam map observations of bright point sources developed during the first commissioning campaign between February and June 2022. With all the observations, we estimate the average positions of each detector with an average error in azimuth of less than 0.70 arcsec and less than 1.05 arcsec in elevation. From the positions, we created the coadded maps of all the detectors, from which we selected only eight observations to calculate the mean beam width of MUSCAT-LMT, of 6.32±0.36 arcsec×5.78±0.19 arcsec. By stacking the maps, we identify the sidelobes with three main structures whose amplitudes are ∼3% with respect to the main beam.
The MUSCAT camera is a second-generation continuum camera at the 50-m Large Millimetre Telescope (LMT) operating in the 1.1 mm band, installed in late 2021 and commissioned in early 2022. The instrument’s focal plane has 1458 horn-coupled lumped-element kinetic inductance detectors (LEKIDs) divided into six arrays deposited on three silicon wafers. This work presents the preliminary on-sky performance results of the focal plane obtained during the commissioning campaign. We characterise the detector’s beam size and shape, mapping the point-like source 3C 279 along the focal plane using raster scans, known as beam mapping. It also allows us to identify which resonance frequencies correspond to each detector located in the focal plane, which leads us to a more complete understanding of the behaviour of the detectors, providing us with a reasonable estimation of the array yield. Finally, we compare these results with those obtained during the characterization of the focal plane in the Cardiff laboratory, previously reported in Tapia et al. 2020.
MUSCAT is a new 1.1 mm band receiver which was installed on the 50 m Large Millimeter Telescope atop Volc´an Sierra Negra in Puebla, Mexico during the final quarter of 2021 and commissioned on sky throughout 2022. MUSCAT uses a novel cooling chain consisting of a commercial pulse tube cooler, two thermal stages of passively-switched continuous sorption coolers, and a final miniature dilution refrigerator. Through this system MUSCAT achieves a continuous temperature of 120 mK at the focal plane and has shown continuous operation at this temperature for greater than 100 days during readiness testing. Through minimising the amount of helium-3 required, the design on MUSCAT’s cryogenic systems produced a reliable, cost-effective cooling platform. Here we present the cryogenic design and performance of MUSCAT on-sky and compare this to that achieved during deployment-readiness testing at Cardiff (UK). We consider both cooldown time and achieved base temperature. We look at the impact on operation of relocating a pulse-tube cooled instrument from a development lab running on a 50 Hz mains electricity supply to a site running at 60 Hz. Finally, we describe the process of preparing the MUSCAT instrument for shipping and assess the success of this process in terms of remedial work required upon arrival.
LiteBIRD is a JAXA-led strategic large-class satellite mission designed to measure the polarization of the cosmic microwave background and Galactic foregrounds from 34 to 448 GHz across the entire sky from L2 in the late 2020s. The scientific payload includes three telescopes which are called the low-, mid-, and high-frequency telescopes each with their own receiver that covers a portion of the mission’s frequency range. The low frequency telescope will map synchrotron radiation from the Galactic foreground and the cosmic microwave background. We discuss the design, fabrication, and characterization of the low-frequency focal plane modules for low-frequency telescope, which has a total bandwidth ranging from 34 to 161 GHz. There will be a total of 4 different pixel types with 8 overlapping bands to cover the full frequency range. These modules are housed in a single low-frequency focal plane unit which provides thermal isolation, mechanical support, and radiative baffling for the detectors. The module design implements multi-chroic lenslet-coupled sinuous antenna arrays coupled to transition edge sensor bolometers read out with frequency-domain mulitplexing. While this technology has strong heritage in ground-based cosmic microwave background experiments, the broad frequency coverage, low optical loading conditions, and the high cosmic ray background of the space environment require further development of this technology to be suitable for LiteBIRD. In these proceedings, we discuss the optical and bolometeric characterization of a triplexing prototype pixel with bands centered on 78, 100, and 140 GHz.
The MUSCAT is a binational collaboration, led by the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) and Cardiff University, dedicated to transfer a variety of skills and experience in the development of technologies for the next generation of sub-mm instrumentation. This primary objective includes the capability to design and fabricate LEKID arrays, design and construct optical, mechanical and cryogenic refrigeration systems operating at temperatures below 150 mK, together with the integration and programming of the readout electronics for multiple detector sub-arrays. The successful development and testing of MUSCAT has provided the Large Millimeter Telescope (LMT) with a large-format millimeter-wavelength camera and a versatile cryogenic platform that can be easily modified to allow the installation of alternative continuum or on-chip spectrometer arrays using different optics, filtering, detector geometries, materials and technologies that can operate at different frequencies.
MUSCAT is a new platform for mm/sub-mm astronomy at the 50m LMT. It is currently configured for 1.1 mm continuum observations with a focal plane consisting of 1458 feedhorn-coupled LEKIDs read out over six frequency division multiplexed RF readout chains with ~250 detectors per readout. We present the performance of the detector readout and tuning system following the initial on-sky commissioning campaign in late 2021. We give details of the readout hardware, the instrument control software, the interfaces between the instrument and telescope control systems, and the automated tuning system for maintaining background-limited performance over the course of an observing night given the varying atmospheric load.
The Mexico-UK Submm Camara for Astronomy (MUSCAT) is a 1.1 mm receiver comprising 1458 Horn-Coupled Lumped Element Kinetic Inductance Detectors (LEKIDs) built through a collaborative effort led by Cardiff University in the UK and the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) in Mexico. MUSCAT was successfully installed on the 50 m diameter Large Millimeter Telescope (LMT) Alfonso Serrano, in December 2021
Here we provide an overview of the MUSCAT platform and present on-sky engineering tests results from scientific commissioning data.
Digital Frequency-Domain Multiplexing (DfMux) is a transition edge sensor multiplexing technique that has been used in mm-wave receivers with multiplexing factors as high as 68. It is the baseline readout technology for LiteBIRD and a potential upscope option for PICO. Recent efforts have been directed toward simplifying packaging, reducing parasitic impedance, and improving readout noise performance by integrating all cryogenic readout components onto a single cryogenic stage. Here we present recent progress including further improved performance and an increase in the scale of operation. This work marks an important step toward the development of DfMux for space-based mm-wave receivers.
The Mexico-UK Submillimetre Camera for AsTronomy (MUSCAT) is a 1.1 mm receiver consisting of 1,500 lumped-element kinetic inductance detectors (LEKIDs) for the Large Millimeter Telescope (LMT; Volcán Sierra Negra in Puebla, México). MUSCAT utilises the maximum field of view of the LMT's upgraded 50-metre primary mirror and is the first México-UK collaboration to deploy a millimetre/sub-mm receiver on the Large Millimeter Telescope. Using a simplistic simulator, we estimate a predicted mapping speed for MUSCAT by combining the measured performance of MUSCAT with the observed sky conditions at the LMT. We compare this to a previously calculated bolometric-model mapping speed and find that our mapping speed is in good agreement when this is scaled by a previously reported empirical factor. Through this simulation we show that signal contamination due to sky fluctuations can be effectively removed through the use of principle component analysis. We also give an overview
MUSCAT is a second-generation continuum camera for the Large Millimeter Telescope (LMT) "Alfonso Serrano", to observe at the 1.1 mm atmospheric window. The camera has 1500 background-limited, horn-coupled lumped- element kinetic inductance detectors (LEKIDs) split across six arrays operating at 130-mK. The detector design for MUSCAT is based on a large-volume, double-meander geometry used as the inductive and two-polarization absorbing section of the LEKID resonator. In this paper we present the optical coupling of the meander to a choked waveguide output, the microwave design of the LEKID architecture, the device fabrication process and results demonstrating the detector sensitivity under a range of optical loads. Also presented are the performance of an aluminum absorbing layer used to minimize the optical cross-talk between detectors.
The Mexico-UK Submillimetre Camera for Astronomy (MUSCAT) is the second-generation large-format continuum camera operating in the 1.1 mm band to be installed on the 50-m diameter Large Millimeter Telescope (LMT) in Mexico. The focal plane of the instrument is made up of 1458 horn coupled lumped-element kinetic inductance detectors (LEKID) divided equally into six channels deposited on three silicon wafers. Here we present the preliminary results of the complete characterisation in the laboratory of the MUSCAT focal plane. Through the instrument's readout system, we perform frequency sweeps of the array to identify the resonance frequencies, and continuous timestream acquisitions to measure and characterise the intrinsic noise and 1/f knee of the detectors. Subsequently, with a re-imaging lens and a blackbody point source, the beams of every detector are mapped, obtaining a mean FWHM size of ~3.27 mm, close to the expected 3.1 mm. Then, by varying the intensity of a beam filling blackbody source, we measure the responsivity and noise power spectral density (PSD) for each detector under an optical load of 300 K, obtaining the noise equivalent power (NEP), with which we verify that the majority of the detectors are photon noise limited. Finally, using a Fourier Transform Spectrometer (FTS), we measure the spectral response of the instrument, which indicate a bandwidth of 1.0-1.2 mm centred on 1.1 mm, as expected.
The next generation of cosmic microwave background (CMB) experiments, such as CMB-S4, will require large arrays of multi-chroic, polarisation-sensitive pixels. Arrays of lumped-element kinetic inductance detectors (LEKIDs) optically coupled through an antenna and transmission line structure are a promising candidate for such experiments. Through initial investigations of small prototype arrays, we have shown this compact device architecture can produce intrinsic quality factors < 10^5, allowing for MUX ratios to exceed 10^3. Moreover, we have demonstrated that additional noise from two-level systems can be reduced to an acceptable level by removing the dielectric from over the capacitive region of the KID, while retaining the microstrip coupling into the inductor. To maximise the efficiency of future focal planes, it is desirable to observe multiple frequencies simultaneously within each pixel. Therefore, we utilise the proven transmission line coupling scheme to introduce band-defining structures to our pixel architecture. Initially targeting the peak of the CMB at 150-GHz, we present a preliminary study of these narrow-band filters in terms of their spectral bandwidth and out of band rejection. By incorporating simple in-line filters we consider the overall impact of adding such structures to our pixel by investigating detector performance in terms of noise and quality factor. Based on these initial results, we present preliminary designs of an optimised mm-wave diplexer that is used to split-up the 150 GHz atmospheric window into multiple sub-bands, before reaching the absorbing length of the LEKID. We present measurements from a set of prototype filter-coupled detectors as the first demonstration towards construction of large-format, multi-chroic, antenna-coupled LEKIDs with the sensitivity required for future CMB experiments.
The Mexico-UK Sub-millimetre Camera for AsTronomy (MUSCAT) is a large-format, millimetre-wave camera consisting of 1,500 background-limited lumped-element kinetic inductance detectors (LEKIDs) scheduled for deployment on the Large Millimeter Telescope (Volcán Sierra Negra, Mexico) in 2018. MUSCAT is designed for observing at 1.1 mm and will utilise the full 40 field of view of the LMTs upgraded 50-m primary mirror. In its primary role, MUSCAT is designed for high-resolution follow-up surveys of both galactic and extra-galactic sub-mm sources identified by Herschel. MUSCAT is also designed to be a technology demonstrator will provide the first on-sky demonstrations of novel design concepts such as horn-coupled LEKID arrays and closed continuous cycle miniature dilution refrigeration.
Here we describe some of the key design elements of the MUSCAT instrument such as the novel use of continuous sorption refrigerators and a miniature dilutor for continuous 100-mK cooling of the focal plane, broadband optical coupling to Aluminium LEKID arrays using waveguide chokes and anti-reflection coating materials as well as with the general mechanical and optical design of MUSCAT. We will explain how MUSCAT is designed to be simple to upgrade and the possibilities for changing the focal plane unit that allows MUSCAT to act as a demonstrator for other novel technologies such as multi-chroic polarisation sensitive pixels and on-chip spectrometry in the future. Finally, we will report on the current status of MUSCAT's commissioning.
In this paper I will describe work done as part of an EU-funded project ‘Far-infrared space interferometer critical assessment’ (FISICA). The aim of the project is to investigate science objectives and technology development required for the next generation THz space interferometer. The THz/FIR is precisely the spectral region where most of the energy from stars, exo-planetary systems and galaxy clusters deep in space is emitted. The atmosphere is almost completely opaque in the wave-band of interest so any observation that requires high quality data must be performed with a space-born instrument. A space-borne far infrared interferometer will be able to answer a variety of crucial astrophysical questions such as how do planets and stars form, what is the energy engine of most galaxies and how common are the molecule building blocks of life. The FISICA team have proposed a novel instrument based on a double Fourier interferometer that is designed to resolve the light from an extended scene, spectrally and spatially. A laboratory prototype spectral-spatial interferometer has been constructed to demonstrate the feasibility of the double-Fourier technique at far infrared wavelengths (0.15 - 1 THz). This demonstrator is being used to investigate and validate important design features and data-processing methods for future instruments. Using electromagnetic modelling techniques several issues related to its operation at long baselines and wavelengths, such as diffraction, have been investigated. These are critical to the design of the concept instrument and the laboratory testbed.
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