The next generation of far-infrared space-based observatories will require large arrays of ultra-sensitive detectors, such as transition edge sensors (TES). We have constructed a new optical testbed in order to perform an end-to-end demonstration of a detector system comprising a 64-pixel TES bolometer array sensitive to the 34—60-micron wavelength range and a frequency domain multiplexing readout with baseband feedback. The testbed contains internal cold (3—35 K) and hot (up to ~300 K) black-body calibration sources, a light pipe for external illumination, and a broadband reference detector for characterizing the spectral content of the calibration sources, as well as reimaging optics for controlling the illumination of detector arrays and an external Fourier transform spectrometer for measuring their spectral response. We present our latest measurements of the optical performance of prototype arrays under multiplexed readout and discuss the implications for future space missions.
SPICA is a mid to far infra-red space mission to explore the processes that form galaxies, stars and planets. SPICA/SAFARI is the far infrared spectrometer that provides near-background limited observations between 34 and 230 micrometers. The core of SAFARI consists of 4 grating modules, dispersing light onto 5 arrays of TES detectors per module. The grating modules provide low resolution (250) instantaneous spectra over the entire wavelength range. The high resolution (1500 to 12000) mode is accomplished by placing a Fourier Transform Spectrometer (FTS) in front of the gratings. Each grating module detector sees an interferogram from which the high resolution spectrum can be constructed. SAFARI data will be a convolution of complex spectral, temporal and spatial information. Along with spectral calibration accuracy of < 1 %, a relative flux calibration of 1% and an absolute flux calibration accuracy of 10% are required. This paper will discuss the calibration strategy and its impact on the instrument design of SAFARI
We present an on-chip superconducting filter bank spectrometer based on transition-edge sensors (TES) as a technology for realising a microwave atmospheric sounding instrument with several hundred channels and sky- noise limited performance. Each device consists of a wideband feed coupled to a transmission line filter bank, with a TES behind each filter. In the first instance we have targeted atmospheric temperature sounding using the oxygen (O2) absorption line at 60 GHz, however the device is being scaled to 180 GHz for humidity sounding. The technology developed is also generally applicable to astronomical instrumentation. We have fabricated a set of test devices to demonstrate key device technologies, such as channel placement, spectral resolution and sensitivity. We will describe device design, test configuration and results.
In context of numerical weather prediction (NWP), increased usage of satellites radiance observations from passive microwave sensors have brought significant improvements in the forecast skills. In the infrared spectral region, hyperspectral sounder instruments such as IASI have already benefitted the NWP assimilation systems, but they are useful only under clear sky conditions. Currently, microwave instruments are providing wealth of information on clouds, precipitation and surface etc., but only with limited number of channels. Furthermore, due to limited number of channels and with poor signal-to-noise ratio, existing passive microwave sensors have very poor resolution and accuracy.
We are currently developing a new microwave instrument concept, based on superconducting filterbank spectrometers, which will enable high spectral resolution observations of atmospheric temperature and humidity profiles across the microwave/sub-millimeter wavelength region with photon-noise-limited sensitivity. This study aims at investigating the information content on temperature and water-vapour that could be provided by such a hyperspectral microwave instrument under clear sky-conditions. Here, we present a new concept of Transition Edge Sensors (TESs)-based hyperspectral microwave instrument for atmospheric sounding applications. In this study, for assessing the impact of hyperspectral sampling in microwave spectral region in clear sky-conditions, we have estimated the information content as standard figure of merit called as degrees of freedom for signal (DFS). The DFS for a set of temperature and humidity sounding channels (50-60 GHz, 118GHz and 183 GHz) have been analyzed under the linear optimal estimation theory framework.
Searching for evidence of inflation by measuring B-modes in the cosmic microwave background (CMB) polarization at degree angular scales remains one of the most compelling experimental challenges in cosmology. BICEP2 and the Keck Array are part of a program of experiments at the South Pole whose main goal is to achieve the sensitivity and systematic control necessary for measurements of the tensor-to-scalar ratio at σ(r) ~0:01. Beam imperfections that are not sufficiently accounted for are a potential source of spurious polarization that could interfere with that goal. The strategy of BICEP2 and the Keck Array is to completely characterize their telescopes' polarized beam response with a combination of in-lab, pre-deployment, and on-site calibrations. We Sereport the status of these experiments, focusing on continued improved understanding of their beams. Far-field measurements of the BICEP2 beam with a chopped thermal source, combined with analysis improvements, show that the level of residual beam-induced systematic errors is acceptable for the goal of σ(r) ~ 0:01 measurements. Beam measurements of the Keck Array side lobes helped identify a way to reduce optical loading with interior cold baffles, which we installed in late 2013. These baffles reduced total optical loading, leading to a ~ 10% increase in mapping speed for the 2014 observing season. The sensitivity of the Keck Array continues to improve: for the 2013 season it was 9:5 μK _/s noise equivalent temperature (NET). In 2014 we converted two of the 150-GHz cameras to 100 GHz for foreground separation capability. We have shown that the BICEP2 and the Keck Array telescope technology is sufficient for the goal of σ(r) ~ 0:01 measurements. Furthermore, the program is continuing with BICEP3, a 100-GHz telescope with 2560 detectors.
The Bicep2 and Keck Array experiments are designed to measure the polarization of the cosmic microwave background (CMB) on angular scales of 2-4 degrees (ℓ = 50–100). This is the region in which the B-mode signal, a signature prediction of cosmic inflation, is expected to peak. Bicep2 was deployed to the South Pole at the end of 2009 and is in the middle of its third year of observing with 500 polarization-sensitive detectors at 150 GHz. The Keck Array was deployed to the South Pole at the end of 2010, initially with three receivers—each similar to Bicep2. An additional two receivers have been added during the 2011-12 summer. We give an overview of the two experiments, report on substantial gains in the sensitivity of the two experiments after post-deployment optimization, and show preliminary maps of CMB polarization from Bicep2.
Bicep2 deployed to the South Pole during the 2009-2010 austral summer, and is now mapping the polarization
of the cosmic microwave background (CMB), searching for evidence of inflationary cosmology. Bicep2 belongs
to a new class of telescopes including Keck (ground-based) and Spider (balloon-borne) that follow on Bicep's
strategy of employing small, cold, on-axis refracting optics. This common design provides key advantages ideal
for targeting the polarization signature from inflation, including: (i) A large field of view, allowing substantial
light collecting power despite the small aperture, while still resolving the degree-scale polarization of the CMB;
(ii) liquid helium-cooled optics and cold stop, allowing for low, stable instrument loading; (iii) the ability to
rotate the entire telescope about the boresight; (iv) a baffled primary aperture, reducing sidelobe pickup; and
(v) the ability to characterize the far field optical performance of the telescope using ground-based sources. We
describe the last of these advantages in detail, including our efforts to measure the main beam shape, beammatch
between orthogonally-polarized pairs, polarization efficiency and response angle, sidelobe pickup, and
ghost imaging. We do so with ground-based polarized microwave sources mounted in the far field as well as
with astronomical calibrators. Ultimately, Bicep2's sensitivity to CMB polarization from inflation will rely on
precise calibration of these beam features.
A. Orlando, R. Aikin, M. Amiri, J. Bock, J. Bonetti, J. Brevik, B. Burger, G. Chattopadthyay, P. Day, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, K. Irwin, M. Kenyon, J. Kovac, C. L. Kuo, A. Lange, H. LeDuc, N. Llombart, H. Nguyen, R. Ogburn, C. Reintsema, M. Runyan, Z. Staniszewski, R. Sudiwala, G. Teply, A. Trangsrud, A. Turner, P. Wilson
BICEP2/Keck and SPIDER are cosmic microwave background (CMB) polarimeters targeting the B-mode polarization
induced by primordial gravitational waves from inflation. They will be using planar arrays of polarization
sensitive antenna-coupled TES bolometers, operating at frequencies between 90 GHz and 220 GHz. At 150 GHz
each array consists of 64 polarimeters and four of these arrays are assembled together to make a focal plane, for a
total of 256 dual-polarization elements (512 TES sensors). The detector arrays are integrated with a time-domain
SQUID multiplexer developed at NIST and read out using the multi-channel electronics (MCE) developed at
the University of British Columbia. Following our progress in improving detector parameters uniformity across
the arrays and fabrication yield, our main effort has focused on improving detector arrays optical and noise
performances, in order to produce science grade focal planes achieving target sensitivities. We report on changes
in detector design implemented to optimize such performances and following focal plane arrays characterization.
BICEP2 has deployed a first 150 GHz science grade focal plane to the South Pole in December 2009.
J. Brevik, R. Aikin, M. Amiri, S. Benton, J. Bock, J. Bonetti, B. Burger, C. Dowell, L. Duband, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, V. Hristov, K. Irwin, J. Kaufman, B. Keating, J. Kovac, C. L. Kuo, A. Lange, E. Leitch, C. Netterfield, H. Nguyen, R. Ogburn, A. Orlando, C. Pryke, C. Reintsema, S. Richter, J. Ruhl, M. Runyan, C. Sheehy, Z. Staniszewski, R. Sudiwala, J. E. Tolan, A. Turner, P. Wilson, C. L. Wong
We report on the preliminary detector performance of the Bicep2 mm-wave polarimeter, deployed in 2009 to
the South Pole. Bicep2 is currently imaging the polarization of the cosmic microwave background at 150 GHz
using an array of 512 antenna-coupled superconducting bolometers. The antennas, band-defining filters and
transition edge sensor (TES) bolometers are photolithographically fabricated on 4 silicon tiles. Each tile consists
of an 8×8 grid of ~7 mm spatial pixels, for a total of 256 detector pairs. A spatial pixel contains 2 sets of
orthogonal antenna slots summed in-phase, with each set coupled to a TES by a filtered microstrip. The detectors
are read out using time-domain multiplexed SQUIDs. The detector pair of each spatial pixel is differenced to
measure polarization. We report on the performance of the Bicep2 detectors in the field, including the focal
plane yield, detector and multiplexer optimization, detector noise and stability, and a preliminary estimate of
the improvement in mapping speed compared to Bicep1.
C. Sheehy, P. Ade, R. Aikin, M. Amiri, S. Benton, C. Bischoff, J. Bock, J. Bonetti, J. Brevik, B. Burger, C. Dowell, L. Duband, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, V. Hristov, K. Irwin, J. Kaufman, B. Keating, J. Kovac, C. L. Kuo, A. Lange, E. Leitch, M. Lueker, C. Netterfield, H. T. Nguyen, R. Ogburn, A. Orlando, C. L. Pryke, C. Reintsema, S. Richter, J. Ruhl, M. Runyan, Z. Staniszewski, S. Stokes, R. Sudiwala, G. Teply, K. Thompson, J. E. Tolan, A. Turner, P. Wilson, C. L. Wong
The Keck Array is a cosmic microwave background (CMB) polarimeter that will begin observing from the South
Pole in late 2010. The initial deployment will consist of three telescopes similar to BICEP2 housed in ultracompact,
pulse tube cooled cryostats. Two more receivers will be added the following year. In these proceedings
we report on the design and performance of the Keck cryostat. We also report some initial results on the
performance of antenna-coupled TES detectors operating in the presence of a pulse tube. We find that the
performance of the detectors is not seriously impacted by the replacement of BICEP2's liquid helium cryostat
with a pulse tube cooled cryostat.
R. W. Ogburn, P. Ade, R. Aikin, M. Amiri, S. Benton, J. Bock, J. Bonetti, J. Brevik, B. Burger, C. Dowell, L. Duband, J. Filippini, S. Golwala, M. Halpern, M. Hasselfield, G. Hilton, V. Hristov, K. Irwin, J. Kaufman, B. Keating, J. Kovac, C. Kuo, A. Lange, E. Leitch, C. Netterfield, H. Nguyen, A. Orlando, C. Pryke, C. Reintsema, S. Richter, J. Ruhl, M. Runyan, C. Sheehy, Z. Staniszewski, S. Stokes, R. Sudiwala, G. P. Teply, J. E. Tolan, A. Turner, P. Wilson, C. L. Wong
The Bicep2 telescope is designed to measure the polarization of the cosmic microwave background on angular
scales near 2-4 degrees, near the expected peak of the B-mode polarization signal induced by primordial gravitational
waves from inflation. Bicep2 follows the success of Bicep, which has set the most sensitive current limits
on B-modes on 2-4 degree scales. The experiment adopts a new detector design in which beam-defining slot antennas
are coupled to TES detectors photolithographically patterned in the same silicon wafer, with multiplexing
SQUID readout. Bicep2 takes advantage of this design's higher focal-plane packing density, ease of fabrication,
and multiplexing readout to field more detectors than Bicep1, improving mapping speed by nearly a factor of
10. Bicep2 was deployed to the South Pole in November 2009 with 500 polarization-sensitive detectors at 150
GHz, and is funded for two seasons of observation. The first months' data demonstrate the performance of the
Caltech/JPL antenna-coupled TES arrays, and two years of observation with Bicep2 will achieve unprecedented
sensitivity to B-modes on degree angular scales.
We describe the design and performance of polarization selective antenna-coupled TES arrays that will be used
in several upcoming Cosmic Microwave Background (CMB) experiments: SPIDER, BICEP-2/SPUD. The fully
lithographic polarimeter arrays utilize planar phased-antennas for collimation (F/4 beam) and microstrip filters
for band definition (25% bandwidth). These devices demonstrate high optical efficiency, excellent beam shapes,
and well-defined spectral bands. The dual-polarization antennas provide well-matched beams and low cross
polarization response, both important for high-fidelity polarization measurements. These devices have so far
been developed for the 100 GHz and 150 GHz bands, two premier millimeter-wave atmospheric windows for
CMB observations. In the near future, the flexible microstrip-coupled architecture can provide photon noise-limited
detection for the entire frequency range of the CMBPOL mission. This paper is a summary of the
progress we have made since the 2006 SPIE meeting in Orlando, FL.
QUaD is a ground-based high-resolution (up to l ≈ 2500) instrument designed to map the polarisation of the Cosmic Microwave Background and to measure its E-mode and B-mode polarisation power spectra. QUaD comprises a bolometric array receiver (100 and 150 GHz) and re-imaging optics on a 2.6-m Cassegrain telescope 2. It will operate for two years and begin observations in 2005. CMB polarisation measurements will require not only a significant increase in sensitivity over earlier experiments but also a better understanding and control of systematic effects particularly those that contribute to the polarised signal. To this end we have undertaken a comprehensive quasi-optical analysis of the QUaD telescope. In particular we have modelled the effects of diffraction on beam propagation through the system. The corrugated feeds that couple radiation from the telescope to phase-sensitive bolometers need to have good beam symmetry and low sidelobe levels over the required bandwidth. It is especially important that the feed horns preserve the polarisation orientation of the incoming fields. We have used an accurate mode-matching model to design such feed horns. In this paper we present the diffraction analysis of the QUaD front-end optics as well as the electromagnetic design and testing of the QUaD corrugated feeds.
After a short analysis of the main problems involved in the
construction of a Far Infrared polarimeter with very low
instrumental noise, we describe the instrument that will be
employed at MITO telescope to search for calibration sources and
investigate polarization near the CMB anisotropy peaks in the next
campaign (Winter 2002-03).
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