arXiv subjects

Thomas Gascard

Publications and source records attributed to Thomas Gascard.

6 recordsLinked to original sources

arXiv2026

Millimeter and sub-millimeter characterization of polymers used for infrared filters in high-sensitivity cryogenic microwave telescopes

Vacuum windows and infrared filters are important transmissive optical components in millimeter receivers, as they hold out the atmosphere and reduce radiative loading on cold stages, thereby improving cryogenic performance. However, the complex optical properties of the materials commonly used for windows and filters are poorly characterized, particularly in-band and in the sub-millimeter regime. The absorption and scattering properties of these materials are becoming increasingly important for designing high-sensitivity millimeter instruments, as their loosely constrained properties are one of the greatest sources of uncertainty remaining in noise modeling. We report the absorption in the millimeter and sub-millimeter regime of nylon 6, nylon 6/6, PTFE and polyethylene (both bulk HDPE and foam HDPE used in radio transparent filter stacks). Additionally, we report the relative power scattered out of the main beam by these materials from 90 to 330 GHz, measured in free space by a robot-enabled scanning vector network analyzer.

astro-ph.IM↗

arXiv2026

Sub-Kelvin Cryogenics for a Super-Pressure Balloon-Borne CMB Polarimeter: Taurus

Taurus is a balloon-borne cosmic microwave background (CMB) experiment designed to operate more than 10,000 transition-edge sensor bolometers at a base temperature near 100 mK during a multi-week stratospheric balloon flight. This platform provides near-space observing conditions while imposing stringent constraints on mass, power, and system robustness, driving the need for a lightweight and highly reliable cryogenic system. To meet these requirements, Taurus employs a multi-stage cryogenic architecture. A 660 L liquid helium tank provides a stable 4 K reservoir, with vapor-cooled shields establishing intermediate stages at approximately 40 K and 80 K. A superfluid helium tank provides an approximately 1.5 K takeoff point for the sub-Kelvin cooling systems. Each of the instrument's three receivers is supported by an independent sub-Kelvin cooling chain that includes closed-cycle 3He sorption refrigerators that cool to 300 mK. These provide the thermal intercept and takeoff for a Chase Research Cryogenics miniature dilution refrigerator that cools the detectors to approximately 100 mK. Here we discuss the requirements and challenges of the Taurus sub-Kelvin cryogenic system and present results of early performance tests.

astro-ph.IM↗

arXiv2024

Vector beam mapping at millimeter wavelengths using a robot arm

Many experimental efforts are striving to provide deep maps of the cosmic microwave background (CMB) to shed light on key questions in modern cosmology. The primary science goal for some of these experiments is to further constrain the energy scale of cosmic inflation. It has been shown that these experiments are particularly sensitive to optical systematics. Near-field vector beam mapping, or holography, is now employed in a variety of CMB-focused experimental efforts due to the technique's ability to provide full details of electromagnetic field propagation through complex systems. In this proceeding, we describe the development of a measurement bench for millimeter-wave phase-sensitive beam mapping with the goal of characterizing optical components for CMB experiments. We discuss the testing of a beam scanner based on a 6-axis robot arm, the related custom control software, the readout architecture, and the overall validation of the system through various testing procedures. Dynamic range of 70 dB is demonstrated for the presented setup. With the current mechanical setup, we derive an upper limits of 45 $\mu$m on the absolute positioning error and 10 $\mu$m on positional repeatability.

astro-ph.IM↗

arXiv2024

Modeling optical systematics for the Taurus CMB experiment

We simulate a variety of optical systematics for Taurus, a balloon-borne cosmic microwave background (CMB) polarisation experiment, to assess their impact on large-scale E-mode polarisation measurements and constraints of the optical depth to reionisation {\tau}. We model a one-month flight of Taurus from Wanaka, New Zealand aboard a super-pressure balloon (SPB). We simulate night-time scans of both the CMB and dust foregrounds in the 150GHz band, one of Taurus's four observing bands. We consider a variety of possible systematics that may affect Taurus's observations, including non-gaussian beams, pointing reconstruction error, and half-wave plate (HWP) non-idealities. For each of these, we evaluate the residual power in the difference between maps simulated with and without the systematic, and compare this to the expected signal level corresponding to Taurus's science goals. Our results indicate that most of the HWP-related systematics can be mitigated to be smaller than sample variance by calibrating with Planck's TT spectrum and using an achromatic HWP model, with a preference for five layers of sapphire to ensure good systematic control. However, additional beam characterization will be required to mitigate far-sidelobe pickup from dust on larger scales.

astro-ph.CO↗

arXiv2021

Design and experimental investigation of a planar metamaterial Silicon based lenslet

The next generations of ground-based cosmic microwave background experiments will require polarisation sensitive, multichroic pixels of large focal planes comprising several thousand detectors operating at the photon noise limit. One approach to achieve this goal is to couple light from the telescope to a polarisation sensitive antenna structure connected to a superconducting diplexer network where the desired frequency bands are filtered before being fed to individual ultra-sensitive detectors such as Transition Edge Sensors. Traditionally, arrays constituted of horn antennas, planar phased antennas or anti-reflection coated micro-lenses have been placed in front of planar antenna structures to achieve the gain required to couple efficiently to the telescope optics. In this paper are presented the design concept and a preliminary analysis of the measured performances of a phase-engineered metamaterial flat-lenslet. The flat lens design is inherently matched to free space, avoiding the necessity of an anti-reflection coating layer. It can be fabricated lithographically, making scaling to large format arrays relatively simple. Furthermore, this technology is compatible with the fabrication process required for the production of large-format lumped element kinetic inductance detector arrays which have already demonstrated the required sensitivity along with multiplexing ratios of order 1000 detectors/channel.

astro-ph.IM↗

arXiv2018

MUSCAT: The Mexico-UK Sub-Millimetre Camera for AsTronomy

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 that 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 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.

astro-ph.IM↗