The Terahertz Intensity Mapper (TIM) is designed to probe the star formation history in dust-obscured star-forming galaxies around the peak of cosmic star formation. This will be done via measurements of the redshifted 157.7 µm line of singly ionized carbon ([CII]). TIM employs two R~250 long-slit grating spectrometers covering 240 to 420 µm. Each is equipped with a focal plane unit containing four wafer-sized subarrays of horn-coupled aluminum kinetic inductance detectors (KIDs). We present the design and performance of a prototype focal plane assembly for one of TIM’s KID-based subarrays. The overall detector package must satisfy thermal and mechanical requirements, while maintaining high optical efficiency and a suitable electromagnetic environment for the KIDs. In particular, our design manages to strictly maintain a 50 µm air gap between the array and the horn block. The prototype detector housing in combination with the first flight-like quadrant were tested at 250 mK. A frequency scan using a vector network analyzer shows 823 resonance features, which represents ⪆90% yield, indicating a good performance of our TIM detector wafer and the whole focal plane unit. Initial measurements also showed that many resonances were affected by collisions and/or very shallow transmission dips as a result of a degraded internal quality factor. This is attributed to the presence of an external magnetic field during cooldown. We report on a study of magnetic field dependence of the quality factor of our quadrant array. We implemented a Helmholtz coil to vary the magnetic field at the detectors by (partially) nulling earth’s. Our investigation shows that the earth magnetic field can significantly affect our KIDs’ performance by degrading the quality factor by a factor of two to five, well below those expected from the operational temperature or optical loading. We find that we can sufficiently recover our detectors’ quality factor by tuning the current in the coils to generate a field that matches earth’s magnetic field in magnitude to within a few µT. We emphasize that it is impractical to fly a Helmholtz coil on TIM and dynamically “null” earth’s. Therefore, it is necessary to employ a properly designed magnetic shield enclosing the TIM focal plane unit. Based on the results presented in this paper, we set a shielding requirement of |B| ⪅3 µT.
The Terahertz Intensity Mapper (TIM) is a balloon-borne far-infrared imaging spectrometer designed to characterize the star formation history of the universe. In its Antarctic science flight, TIM will map the redshifted 158um line of ionized carbon over the redshift range 0.5-1.7 (lookback times of 5-10 Gyr). TIM will spectroscopically detect ~100 galaxies, determine the star formation rate history over this time interval through line intensity mapping, and measure the stacked CII emission from galaxies in its well-studied target fields (GOODS-S, SPT Deep Field). TIM consists of a 2-meter telescope feeding two grating spectrometers that that cover 240-420um at R~250 across a 1.3deg field of view, detected with 7200 kinetic inductance detectors and sampled through a novel RF system-on-chip readout. TIM will serve as an important scientific instrument, accessing wavelengths that cannot easily be studied from the ground, and as a testbed for future FIR space technology.
TIM, the Terahertz Intensity Mapper, is a NASA far-infrared balloon mission designed to perform [CII] intensity mapping of the peak of cosmic star formation. To achieve this goal, TIM will fly two grating spectrometers that together cover the 240 to 420 um wavelength range at an R~250. Each spectrometer will require large format arrays (4x~900 detectors) of dual-polarization sensitive detectors, which are photon noise limited at 100 fW of loading. We will present the design of a fully-aluminum lumped-element kinetic-inductance detector (KID) that incorporates a novel “chain-link” absorber design. Operating at 215 mK, we demonstrate that this detector achieves a photon noise limited performance at 80 fW of optical loading with a white noise spectrum down to 1 Hz. Informed by dark measurements, we except these KIDs to achieve a detector limited NEP of 2e-18 W/rt(Hz) at a loading <10 fW. In addition, we shall show our design of a kilopixel array and its initial performance measurements.
KEYWORDS: Superconductors, Multiplexing, Sensors, Data communications, Telecommunications, Microwave radiation, Astronomy, System on a chip, Algorithm development, Telescopes
We describe the development of a reconfigurable frequency multiplexed readout system for superconducting arrays. This system is an upgrade to the ROACH2 based readout system we have developed for a number of balloon-borne and ground-based instruments including BLAST-TNG, OLIMPO, MUSCAT, Superspec and TolTEC. Specifically our development has targeted the RFSoC ZCU111 evaluation board of which the size, weight, power, and instantaneous bandwidth have made it an attractive candidate for future balloon-borne or space-based astronomical instruments. Applications for the new readout system focus primarily on: frequency multiplexed superconducting nanowires single-photon detectors, Kinetic inductance detectors, Transition Edge Sensors, and Quantum Capacitance detectors. We will discuss the overlapping readout requirements that drive the general firmware architecture. Preliminary measurements with the new readout system using different detector technologies will also be presented.
Microwave kinetic inductance detectors (MKIDs) operate through means of a superconducting resonator that changes resonant frequency and quality factor when incident photons are absorbed in the superconducting material. Incident power on MKIDs is determined by reading out the phase and amplitude of a tone injected into each detector. However, if the incident power on an MKID changes too drastically and the resonant frequency moves too far from the probe tone, amplitude information becomes useless and the detector is effectively out of commission until a VNA sweep is used to relocate resonances. Here we present the designs and preliminary results of a tone-tracking firmware that uses phase information to maintain an on-resonance probe tone at all times, removing the need for time-intensive VNA sweeps during observations and effectively maximizing the dynamic range of MKIDs. We will conclude with a discussion on future NASA missions that hope implement this tone-tracking design.
Here we present the preliminary and final designs of a low-mass, low-power, highly integrated Schottky diode based coherent receiver system suitable for deployment on cubesat or other small satellite platforms. Currently, coherent Schottky receivers are far too large and consume too much power to be considered for deployment on any smaller forms of space-based satellites. Using an already existing design for a modular 520-600 GHz receiver designed at JPL, we have used novel packaging methods to condense this receiver into an integrated system. This integrated receiver has shown to have a volume and power consumption significantly smaller than the current state of the art. We will further present the designs of a similar integrated receiver for the first excited state of water vapor operating at the 1040-1200 GHz range. Finally, we discuss future plans for the combined mixer system and its potential for use in cubesat interferometry systems.
While great strides have been made in far-infrared astrophysics with the NASA Spitzer and ESA Herschel missions, subarcsecond spatial resolution from space is still beyond the reach of current technologies. The Atacama Large Millimeter Array has produced stunning images from the ground of planetary systems in the process of formation but cannot observe the key molecules of water or O2, due to the presence of Earth’s atmosphere. The concept presented here will enable interferometric imaging with sub-arcsecond resolution of water and other key far infrared molecular species from space at a cost far lower than the flagship class interferometric missions previously proposed (i.e. ESA’s ESPRIT). We present a concept for a far infrared interferometer based on a constellation of CubeSat antenna elements with a central ESPA-class correlator satellite optimized for the imaging of water in protoplanetary systems. Such a mission would produce groundbreaking images of newly forming planetary systems in a key astrophysical and astrobiological tracer, the 557 GHz ground state line of water. By leveraging recent developments in CubeSat technology, inflatable reflectors, miniaturized receiver systems and low power CMOS digital electronics, such a mission could be implemented at an Explorer level budget. In addition to the proposed astrophysics application, the developments proposed here could also find application in planetary science (FIR spectroscopy of comets and small bodies) and Earth observing (high resolution imaging of Earth from geostationary orbit).
KEYWORDS: CMOS technology, Spectroscopy, Clocks, Signal processing, Astronomy, Digital electronics, Field programmable gate arrays, Astrophysics, Space operations
Here we present the characterization of the performance of a novel design for a digital spectrometer that could be used for high resolution cm/mm/submm spectroscopy. The CMOS ASIC spectrometer design, developed at JPL and UCLA, has dramatically lower power consumption than current approaches that generally employ Field Programmable Gate Arrays (FPGAs). Particularly for space missions and for small satellites, power consumption is a major issue. The order of magnitude lower power consumption of the ASIC approach is thus critical for future missions employing large-format focal plane arrays. Our task was to evaluate this 1024 channel, 1.3-GHz bandwidth CMOS spectrometer in terms of stability and filter shape. The chip was to be tested largely at half-maximum speed to allow for use of the polyphase filter bank. The results of this testing show that the ASIC spectrometer can be made to perform largely as expected based on its design parameters, however, they suggest that more testing of the spectrometer chip could be beneficial. Follow-up tests and newer versions of the chip are discussed at the end of the proceeding.
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