Millimeter wavelength radiation holds promise for detection of security threats at a distance, including suicide bomb belts and maritime threats in poor weather. The high sensitivity of superconducting Transition Edge Sensor (TES) detectors makes them ideal for passive imaging of thermal signals at these wavelengths. We have built a 350 GHz video-rate imaging system using a large-format array of feedhorn-coupled TES bolometers. The system operates at a standoff distance of 16m to 28m with a spatial resolution of 1:4 cm (at 17m). It currently contains one 251-detector subarray, and will be expanded to contain four subarrays for a total of 1004 detectors. The system has been used to take video images which reveal the presence of weapons concealed beneath a shirt in an indoor setting. We present a summary of this work.
We are developing a 350 GHz cryogenic passive video imaging system for use in standoff security applications.
This demonstration system uses 800 photon-noise-limited superconducting transition edge sensor bolometers,
read out using a time-division multiplexed readout system. It will image a 1 m x 1 m field of view at a standoff
distance of 16 m to a resolution of approximately 1 cm at video frame rates (20 frames per second). High spatial
resolution is achieved by the use of an f/2.0 Cassegrain optical system with 1.3 m primary mirror. Preliminary
dark and optical testing of prototype detectors indicates that we can achieve a noise equivalent temperature
difference (NETD) below 100 mK for the fully sampled 1 m x 1 m image at 20 frames per second. We report
on the current status of development of this system.
We are developing a 350 GHz cryogenic passive video imaging system. This demonstration system uses 800
photon-noise-limited superconducting transition edge sensor bolometers. It will image a 1 m x 1 m area at a
standoff distance of 16 m to a resolution of approximately 1 cm at video frame rates (20 frames per second).
High spatial resolution is achieved by the use of an f/2.0 Cassegrain optical system with 1.3 m primary mirror.
Preliminary testing of prototype detectors indicates that we can achieve a noise equivalent temperature difference
(NETD) of 70 mK for the fully sampled 1 m × 1 m image at 20 frames per second.
CℓOVER is a multi-frequency experiment optimised to measure
the Cosmic Microwave Background (CMB) polarization, in
particular the B-mode component. CℓOVER comprises two
instruments observing respectively at 97 GHz and 150/225 GHz.
The focal plane of both instruments consists of an array of
corrugated feed-horns coupled to TES detectors cooled at 100
mK. The primary science goal of CℓOVER is to be sensitive to
gravitational waves down to r ~ 0.03 (at 3σ)in two years of operations.
SCUBA-2 is an innovative 10,000 pixel submillimeter camera due to be delivered to the James Clerk Maxwell Telescope in late 2006. The camera is expected to revolutionize submillimeter astronomy in terms of the ability to carry out wide-field surveys to unprecedented depths addressing key questions relating to the origins of galaxies, stars and planets. This paper presents an update on the project with particular emphasis on the laboratory commissioning of the instrument. The assembly and integration will be described as well as the measured thermal performance of the instrument. A summary of the performance results will be presented from the TES bolometer arrays, which come complete with in-focal plane SQUID amplifiers and multiplexed readouts, and are cooled to 100mK by a liquid cryogen-free dilution refrigerator. Considerable emphasis has also been placed on the operating modes of the instrument and the "common-user" aspect of the user interface and data reduction pipeline. These areas will also be described in the paper.
We present the results of characterization measurements on a 1280 pixel superconducting bolometer array designed for operation at wavelengths around 450 μm. The array is a prototype for the sub-arrays which will form the focal plane for the SCUBA-2 sub-mm camera, being built for the James Clerk Maxwell Telescope (JCMT) in Hawaii. With over 10 000 pixels in total, it will provide a huge improvement in both sensitivity and mapping speed over existing instruments. The array consists of molybdenum-copper bi-layer TES (transition edge sensor) pixels, bonded to a multiplexer. The detectors operate at a
temperature of approximately 175 mK, and require a heat sink at a temperature of approximately 60 mK. In contrast to previous TES arrays, the multiplexing elements are located beneath each pixel (an "in-focal plane" configuration). We present the results of electrical and optical measurements, and show that the optical NEP (noise equivalent power) is less than 1.4 × 10-16 W Hz-0.5 and thus within the goal of 1.5 × 10-16 W Hz-0.5.
SCUBA-2 is a new wide-field submillimeter camera under construction for the James Clerk Maxwell Telescope
on Mauna Kea in Hawaii. SCUBA-2 images simultaneously at 450 and 850 μm using large-scale arrays of
superconducting bolometers, with over five thousand pixels at each wavelength. Time division multiplexed
readouts and cryogenic amplifiers, both based on superconducting quantum interference devices (SQUIDs), are
also used in the design. The SCUBA-2 detector arrays must be well shielded against magnetic fields, since the
performance of the bolometers can be seriously affected by the presence of a strong field, and the SQUIDs are
themselves sensitive magnetometers. This shielding is to be provided by a combination of high-permeability and
superconducting layers on both the ambient temperature and cryogenic stages of the instrument. To optimise
and demonstrate the effectiveness of the shielding design, a finite-element modelling method was employed, using
the Ansoft(R) Maxwell 3DTM package. Although a number of approximations had to be made in the modelling,
the finite-element results allow a good estimation of the effectiveness of the shielding at attenuating external
magnetic fields to be made. This paper describes the modelling process, outlines the key results and summarises
the final shielding design.
CℓOVER is an experiment which aims to detect the signature of gravitational waves from inflation by measuring
the B-mode polarization of the cosmic microwave background. CℓOVER consists of three telescopes operating
at 97, 150, and 220 GHz. The 97-GHz telescope has 160 horns in its focal plane while the 150 and 220-GHz
telescopes have 256 horns each. The horns are arranged in a hexagonal array and feed a polarimeter which
uses finline-coupled TES bolometers as detectors. To detect the two polarizations the 97-GHz telescope has 320 detectors while the 150 and 220-GHz telescopes have 512 detectors each. To achieve the required NEPs the
detectors are cooled to 100 mK for the 97 and 150-GHz polarimeters and 230 mK for the 220-GHz polarimeter.
Each detector is fabricated as a single chip to guarantee fully functioning focal planes. The detectors are
contained in linear modules made of copper which form split-block waveguides. The detector modules contain
16 or 20 detectors each for compatibility with the hexagonal arrays of horns in the telescopes' focal planes. Each
detector module contains a time-division SQUID multiplexer to read out the detectors. Further amplification of
the multiplexed signals is provided by SQUID series arrays. The first prototype detectors for CℓOVER operate
with a bath temperature of 230 mK and are used to validate the detector design as well as the polarimeter
technology. We describe the design of the CℓOVER detectors, detector blocks, and readout, and give an update
on the detector development.
SCUBA-2 is the next-generation replacement for SCUBA (Sub-millimetre
Common User Bolometer Array) on the James Clerk Maxwell Telescope. Operating at 450 and 850 microns, SCUBA-2 fills the focal plane of the telescope with fully-sampled, monolithic bolometer arrays. Each SCUBA-2 pixel uses a quarter-wave slab of silicon with an implanted resistive layer and backshort as an absorber and a superconducting transition edge sensor as a thermometer. In order to verify and optimize the pixel design, we have investigated the electromagnetic behaviour of the detectors, using both a simple transmission-line model and Ansoft HFSS, a finite-element electromagnetic simulator. We used the transmission line model to fit transmission measurements of doped wafers and determined the correct implant dose for the absorbing layer. The more detailed HFSS modelling yielded some unexpected results which led us to modify the pixel design. We also verified that the detectors suffered little loss of sensitivity for off-axis angles up to about 30 degrees.
SCUBA-2, which replaces SCUBA (the Submillimeter Common User Bolometer
Array) on the James Clerk Maxwell Telescope (JCMT) in 2006, is a
large-format bolometer array for submillimeter astronomy. Unlike previous detectors which have used discrete bolometers, SCUBA-2 has two dc-coupled, monolithic, filled arrays with a total of ~10,000 bolometers. It will offer simultaneous imaging of a 50 sq-arcmin field of view at wavelengths of 850 and 450 microns. SCUBA-2 is expected to have a huge impact on the study of galaxy formation and evolution in the early Universe as well as star and planet formation in our own Galaxy. Mapping the sky to the same S/N up to 1000 times faster than SCUBA, it will also act as a pathfinder for the new submillimeter interferometers such as ALMA. SCUBA-2's absorber-coupled pixels use superconducting transition edge sensors operating at 120 mK for performance limited by the sky background photon noise. The monolithic silicon detector arrays are deep-etched by the Bosch process to isolate the pixels on silicon nitride membranes. Electrical
connections are made through indium bump bonds to a SQUID time-domain multiplexer (MUX). We give an overview of the SCUBA-2 system and an update on its status, and describe some of the technological innovations that make this unique instrument possible.