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Spectral-spatial interferometry pioneered in a narrow band in the near infrared has not enjoyed much exploitation as a technique. Proposed as a promising modulation method for a potential Far-infrared future satellite, a period of study was performed on two testbeds to improve and evolve this technique in the laboratory in order to simplify some of the technical aspects and the data analysis involved. Here we will present an update on the successful upgrade of a previous wideband millimetric (0.3-1.0 THz) testbed to a far-IR (11-14THz) one, as well as the ongoing progress on a broadband setup for an imaging system with a commercial thermal-or mid-IR (8 to 12 micron or 25-35 THz) camera currently working as imaging FTS. Source size, coherence and technical issues are discussed.

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.

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.

Lumped-element Kinetic Inductance Detectors (LEKIDs) are superconducting Inductor-Capacitor (LC) resonators that have been utilised in large-format arrays of detectors for millimetre-wave astronomy. LEKIDs are highly multiplex-able by design and have been demonstrated to reach the photon-noise limit required for astronomy. However, coupling such structures directly to low loss superconducting transmission lines and filtering structures has proved challenging. The research presented in this thesis is aimed at developing techniques for coupling a LEKID to an antenna structure and microwave transmission line, which would be compatible with existing device architecture used in existing Cosmic Microwave Background (CMB) experiments. Several important developments towards realising large arrays of multi-chroic, polarisation-sensitive pixels suitable for future Cosmic Microwave Background experiments are presented in this thesis. These include coupling a Kinetic Inductance Detector (KID) to an antenna and microstrip, which is made possible by the separated inductor and capacitor architecture of a LEKID. The results presented in this thesis demonstrate that a dielectric can be deposited over the inductor only, to form a coupling microstrip structure, while leaving the LEKID relatively immune to the noise created by the typically noisy dielectrics. The section of microstrip between the antenna and KID can then be utilised to introduce on-chip filtering structures which limit the band of frequencies reaching the detector. Initial measurements of single-colour prototype devices suggest the current devices are susceptible to stray light, an issue that needs to be considered in future design iterations. However, the overall results presented in this thesis still represent an important step towards realising large arrays of multi-chroic, polarisation-sensitive detectors required for future studies of the CMB.

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 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

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 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.

Lumped-element Kinetic Inductance Detectors (LEKIDs) are superconducting Inductor-Capacitor (LC) resonators that have been utilised in large-format arrays of detectors for millimetre-wave astronomy. LEKIDs are highly multiplex-able by design and have been demonstrated to reach the photon-noise limit required for astronomy. However, coupling such structures directly to low loss superconducting transmission lines and filtering structures has proved challenging. The research presented in this thesis is aimed at developing techniques for coupling a LEKID to an antenna structure and microwave transmission line, which would be compatible with existing device architecture used in existing Cosmic Microwave Background (CMB) experiments. Several important developments towards realising large arrays of multi-chroic, polarisation-sensitive pixels suitable for future Cosmic Microwave Background experiments are presented in this thesis. These include coupling a Kinetic Inductance Detector (KID) to an antenna and microstrip, which is made possible by the separated inductor and capacitor architecture of a LEKID. The results presented in this thesis demonstrate that a dielectric can be deposited over the inductor only, to form a coupling microstrip structure, while leaving the LEKID relatively immune to the noise created by the typically noisy dielectrics. The section of microstrip between the antenna and KID can then be utilised to introduce on-chip filtering structures which limit the band of frequencies reaching the detector. Initial measurements of single-colour prototype devices suggest the current devices are susceptible to stray light, an issue that needs to be considered in future design iterations. However, the overall results presented in this thesis still represent an important step towards realising large arrays of multi-chroic, polarisation-sensitive detectors required for future studies of the CMB.