Prime-Cam is a first-generation instrument for the Cerro Chajnantor Atacama Telescope-prime (CCAT-prime) Facility. The 850 GHz module for Prime-Cam will probe the highest frequency of all the instrument modules. We describe the parameter space of the 850 GHz optical system between the Fλ spacing, beam size, pixel sensitivity, and detector count. We present the optimization of an optical design for the 850 GHz instrument module for CCAT-prime. We further describe the development of the cryogenic RF chain design to accommodate 30 readout lines to read 41,400 kinetic inductance detectors (KIDs) within the cryogenic testbed.
The Fred Young Submillimeter Telescope (FYST) at the Cerro-Chajnantor Atacama Telescope prime (CCATprime) Facility will host Prime-Cam as a powerful, first generation camera with imaging polarimeters working at several wavelengths and spectroscopic instruments aimed at intensity mapping during the Epoch of Reionization. Here we introduce the 850 GHz (350 micron) instrument module. This will be the highest frequency module in Prime-Cam and the most novel for astronomical and cosmological surveys, taking full advantage of the atmospheric transparency at the high 5600 meter CCAT-prime siting on Cerro Chajnantor. The 850 GHz module will deploy ∼40,000 Kinetic Inductance Detectors (KIDs) with Silicon platelet feedhorn coupling (both fabricated at NIST), and will provide unprecedented broadband intensity and polarization measurement capabilities. The 850 GHz module will be key to addressing pressing astrophysical questions regarding galaxy formation, Big Bang cosmology, and star formation within our own Galaxy. We present the motivation and overall design for the module, and initial laboratory characterization.
Scientists must reconsider the design of cryogenically cooled spectrometers in order to fully exploit the ever-increasing sensitivity of superconducting far-infrared bolometers. While Fourier transform spectrometers (FTS) have an illustrious history in astronomical research, the sensitivity of modern detectors is such that the multiplex disadvantage of FTS is prohibitive unless the spectral bandpass can be restricted to a few tenths of one percent. One method of achieving this goal is to use a diffraction grating as a post-dispersing component. Unlike a typical FTS, in which a single detector simultaneously measures a broad spectral band, a post-dispersed detection system requires multiple detectors, each with their own unique spectral, spatial and temporal responses. Moreover, the narrow spectral band viewed by each detector results in an interferogram having a large coherence length. In general, the signal is heavily modulated, yet truncated. While simulations play a useful role in modeling instrumental performance, there is no substitute for data obtained from a real implementation of an instrument concept. In this paper we describe the development of a cryogenic, far-infrared, post-dispersed, polarizing FTS (PDPFTS). The end-to-end performance of the PDPFTS will be evaluated in a large cryogenic test facility to simulate a space environment. The results provide valuable insight into the spectral calibration and data processing challenges that will be faced by hybrid spectrometers employing a post-dispersed component.
The continued improvement in the sensitivity of superconducting far-infrared bolometers necessitates improved designs of cryogenically cooled broadband spectrometers in order to fully exploit the potential of such detectors. While Fourier transform spectrometers (FTS) have an illustrious history in astronomical research, the sensitivity of state-of-the-art detectors is such that the multiplex disadvantage of FTS is prohibitive unless the spectral bandpass can be restricted to less than 1%. One method of achieving this goal, and the one that has been adopted for the SPICA SAFARI instrument, is to use a diffraction grating as the post-dispersing component. Unlike a typical FTS, in which a single detector simultaneously measures a broad spectral band, a post-dispersed detection system requires multiple detectors, each with their own unique spectral, spatial, and temporal responses. Moreover, the narrow spectral band viewed by each detector results in an interferogram having a large coherence length; the signal is heavily modulated, yet truncated. While simulations play a useful role in modeling instrumental performance, there is no substitute for data obtained from a real implementation of an instrument concept. In this paper we describe the development and current status of a cryogenic, far-infrared, postdispersed, polarizing FTS (PDPFTS): a demonstrator for the SPICA SAFARI instrument.
Over half of the light incident on the Earth from the Universe falls within the Far-Infrared (FIR) region of the spectrum. Due to the deleterious effects of the Earth's atmosphere and instrument self-emission, astronomical measurements in the FIR require space-borne instrumentation operating at cryogenic temperatures. These instruments place stringent constraints on the mechanical and thermal properties of the support structures at low temperatures. With high stiffness, tensile strength, strength-to-mass ratio, and extremely low thermal conductivity, carbon fibre reinforced polymers (CFRPs) are an important material for aerospace and FIR astronomical applications, however, little is known about their properties at cryogenic temperatures. We have developed a test facility for exploring CFRP properties down to 4 K. We present results from our ongoing study in which we compare and contrast the performance of CFRP samples using different materials, and multiple layup configurations. Current results include an evaluation of a cryostat dedicated for materials testing and a custom cryogenic metrology system, and preliminary cryogenic thermal expansion measurements. The goal of this research is to explore the feasibility of making CFRP-based, lightweight, cryogenic astronomical instruments.
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