The mm-wavelength sky reveals the initial phase of structure formation, at all spatial scales, over the entire observable history of the Universe. Over the past 20 years, advances in mm-wavelength detectors and camera systems have allowed the field to take enormous strides forward – particularly in the study of the Cosmic Microwave Background – but limitations in mapping speeds, sensitivity and resolution have plagued studies of astrophysical phenomena. In fact, limitations due to inherent biases in the ground-based mm-wavelength surveys conducted over the last 2 decades continue to motivate the need for deeper and wider-area maps made with increased angular resolution. TolTEC is a new camera that will fill the focal plane of the 50m diameter Large Millimeter Telescope (LMT) and provide simultaneous, polarization-sensitive imaging at 2.0, 1.4, and 1.1mm wavelengths. The instrument, now under construction, is a cryogenically cooled receiver housing three separate kilo-pixel arrays of Kinetic Inductance Detectors (KIDs) that are coupled to the telescope through a series of silicon lenses and dichroic splitters. TolTEC will be installed and commissioned on the LMT in early 2019 where it will become both a facility instrument and also perform a series of 100 hour “Legacy Surveys” whose data will be publicly available. The initial four surveys in this series: the Clouds to Cores Legacy Survey, the Fields in Filaments Legacy Survey, the Ultra-Deep Legacy Survey and the Large Scale Structure Survey are currently being defined in public working groups of astronomers coordinated by TolTEC Science Team members. Data collection for these surveys will begin in late 2019 with data releases planned for late 2020 and 2021. Herein we describe the instrument concept, provide performance data for key subsystems, and provide an overview of the science, schedule and plans for the initial four Legacy Survey concepts.
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 <i>Herschel</i>. 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.<p> </p> 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.
We present the design of a cryogenic system for testing different technologies of millimeter wavelength detectors. The proposed design is developed at the Astronomical Instrumentation Laboratory for Millimeter Wavelength at the National Institute of Astrophysics, Optics and Electronics, in México. The cryogenic system is integrated by a closed cycle pulse tube cooler with a 4 Kelvin 12 inches cold plate and a He-4/He-3 fridge and would be able to characterize KIDs (Kinetic Inductor Detectors), TES (Transition Edge Sensors) or semiconductor bolometers using a thermal link to a 250 mK stage. Readout electronics will be installed at the 4 Kelvin cold plate along with connectors and cables for the thermometry. In this paper we present a preliminary 3D model design which its main goal is to use efficiently the limited space in the cryostat with emphasis on the interchangeability for installing each time any of the three different detector technologies in the same cold plate; results for the thermal calculations and finite-element modeling are also shown. The system would allow, with some minor changes, to replace the He-4/He-3 fridge by a dilution fridge in order to reach temperatures about 100 mK to have more flexibility in the detector testing. The importance of the cryogenic test bench relies in the need for an easier and quicker characterization of detectors arrays as part of the research for the development of instruments for millimeter telescopes.
We present the characterization of a boron doped hydrogenated amorphous silicon (a-Si:H) thermosensor bolometer
array for far infrared detection. The array was fabricated over a silicon wafer on a 0.4 μm silicon-nitride (Si<sub>3</sub>N<sub>4</sub>) layer.
Wet bulk micromachining was used to create pixels of suspended nitride film by removing the silicon underneath. On
this film, a boron doped a-Si:H layer was deposited using a low frequency PECVD system at 540 K. Conventional
lithography was used to define the bolometers on the nitride windows, and the 5 × 5 microbolometer array was fabricated
and characterized at 77 K. A 1.17 x 10<sup>-2</sup> mA/W responsivity, with a temperature coefficient of resistance (TCR) of
4.25%, were obtained.