From the ultraviolet to the infrared, modern astronomical spectrographs are workhorse instruments at any wide-purpose observatory, enabling both follow-up and survey science across all fields of astrophysics and astronomy. As the critical optical element of determining the performance of any spectrograph, the key parameters of the dispersing element —resolution, throughput, bandwidth, and dispersion — must all be optimized for highest performance of the instrument. There are a growing number of alternatives in the domain of diffraction gratings and dispersing elements thanks to the development of new technologies (from holography to lithography and micromachining). Some of these technologies are not specifically developed for astronomy, but have exciting potential applications in this field. In order to make the best design choices for new instrumentation, it is necessary to understand the advantages and the limitations of each technology. Although many of the new developments will naturally focus on instrumentation for the new generation of Extremely Large Telescopes, any new developments will leverage the scientific impact of the small and medium facilities as well. In this talk, the outcomes of a dedicated workshop organized in October 2017 will be reported. The goals of that workshop were to bringing together scientists and engineers involved in the design and construction of spectrographs with our commercial partners who help produce and develop the necessary technology.
The construction of the next generation of 40 m-class astronomical telescopes poses an enormous challenge for the design of their instruments and the manufacture of their optics. Optical elements typically increase in both size and number, placing ever more demands on the system manufacturing and alignment tolerances. This challenge can be met by using the wider design space offered by freeform optics, by for instance allowing highly aspherical surfaces. Optical designs incorporating freeform optics can achieve a better performance with fewer components. This also leads to savings in volume and mass and, potentially, cost.
This paper describes the characterization of the FAME system (freeform active mirror experiment). The system consists of a thin hydroformed face sheet that is produced to be close to the required surface shape, a highly controllable active array that provides support and the ability to set local curvature of the optical surface and the actuator layout with control electronics that drives the active array.
A detailed characterisation of the fully-assembled freeform mirror was carried out with the physical and optical properties determined by coordinate measurements (CMM), laser scanning, spherometry and Fizeau interferometry. The numerical model of the mirror was refined to match the as-built features and to predict the performance more accurately.
Each of the 18 actuators was tested individually and the results allow the generation of look-up tables providing the force on the mirror for each actuator setting. The actuators were modelled with finite element analysis and compared to the detailed measurements to develop a closed-loop system simulation. After assembling the actuators in an array, the mirror surface was measured again using interferometry. The influence functions and Eigen-modes were also determined by interferometry and compared to the FEA results.
This paper investigates the potential role of small satellites, specifically those often referred to as CubeSats, in the future of infrared astronomy. Whilst CubeSats are seen as excellent (and inexpensive) ways to demonstrate and improve the readiness of critical (space) technologies of the future they also potentially have a role in solving key astrophysical problems. The pros and cons of such small platforms are considered and evaluated with emphasis on the technological limitations and how these might be improved. Three case studies are presented for applications in the IR region. One of the main challenges of operating in the IR is that the detector invariably needs to be cooled. This is a significant undertaking requiring additional platform volume and power and is one of the major areas of discussion in this paper. Whilst the small aperture on a CubeSat inevitably has limitations both in terms of sensitivity and angular resolution when compared to large ground-based and space-borne telescopes, the prospect of having distributed arrays of tens (perhaps hundreds) of IR-optimised CubeSats in the future offers enormous potential. Finally, we summarise the key technology developments needed to realise the case study missions in the form of a roadmap.
For over two decades, astronomers have considered the possibilities for interferometry in space. The first of these missions was the Space Interferometry Mission (SIM), but that was followed by missions for studying exoplanets (e.g Terrestrial Planet Finder, Darwin), and then far-infrared interferometers (e.g. the Space Infrared Interferometric Telescope, the Far-Infrared Interferometer). Unfortunately, following the cancellation of SIM, the future for space-based interferometry has been in doubt, and the interferometric community needs to reevaluate the path forward. While interferometers have strong potential for scientific discovery, there are technological developments still needed, and continued maturation of techniques is important for advocacy to the broader astronomical community. We review the status of several concepts for space-based interferometry, and look for possible synergies between missions oriented towards different science goals.
SCUBA-2 is a state of the art wide field camera on the JCMT. SCUBA-2 has been fully operational since November
2011, producing a wide range of science results, including a unique series of survey programs. A new large survey
programme commenced in 2015, which included for the first time, polarisation sensitive measurements using POL-2, the
polarimeter ancillary instrument. We discuss proposals and the science case for upgrading SCUBA-2 with new detector
arrays that will keep SCUBA-2 and the JCMT at the forefront of continuum submillimetre science.
instrument’s twin focal planes, each with over 5000 superconducting Transition Edge Sensors (TES) that work simultaneously at 450 and 850 microns are producing excellent science results and in particular a unique series of JCMT legacy surveys. In this paper we give an update on the performance of the instrument over the past 2 years of science operations and present the results of a study into the noise properties of the TES arrays. We highlight changes that have been implemented to increase the efficiency and performance of SCUBA-2 and discus the potential for future enhancements.
SCUBA-2 is a wide-field submillimeter bolometer camera operating at the James Clerk Maxwell Telescope. The camera has twin focal planes, each with 5120 superconducting Transition Edge Sensors, which provide simultaneous images in two filter bands at 450 and 850 microns matched to the atmospheric windows. Detailed knowledge of the optical filter profiles that define these bands is important for estimating potential contamination from the prevalent CO J = 3-2 and CO 6-5 line emission, and correctly interpreting the effects of the source spectral index on photometric observations. We present measurements of the spectral response of SCUBA-2 obtained with FTS-2, the ancillary Fourier transform spectrometer instrument at the JCMT. The spectral measurements will be compared with the predicted filter profile determined from the linear combination of the individual filter profiles present in the SCUBA-2 optical train.
SCUBA-2 is the largest submillimetre wide-field bolometric camera ever built. This 43 square arc- minute field-of-view instrument operates at two wavelengths (850 and 450 microns) and has been installed on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. SCUBA-2 has been successfully commissioned and operational for general science since October 2011. This paper presents an overview of the on-sky performance of the instrument during and since commissioning in mid- 2011. The on-sky noise characteristics and NEPs of the 450 μm and 850 μm arrays, with average yields of approximately 3400 bolometers at each wavelength, will be shown. The observing modes of the instrument and the on-sky calibration techniques are described. The culmination of these efforts has resulted in a scientifically powerful mapping camera with sensitivities that allow a square degree of sky to be mapped to 10 mJy/beam rms at 850 μm in 2 hours and 60 mJy/beam rms at 450 μm in 5 hours in the best weather.
Cryogen free or ‘dry’ dilution refrigerators that integrate a cryocooler such as a two stage pulse tube to replace the conventional liquid helium bath and 1K pot, have become a practical alternative for cooling astronomical detectors to mK temperatures and offer many advantages. SCUBA-2, the new submillimetre camera in operation at the JCMT, on the summit of Mauna Kea, Hawaii, was one of the first instruments to use such a fridge design. The dry dilution fridge for SCUBA-2 has now been in service for almost 4 years during commissioning at JCMT. In the most recent astronomical commissioning phase, the dilution fridge was in continuous operation for 10 months with no loss of base temperature or cooling power, cooling the SCUBA-2 detector arrays to below 100mK while maintaining a further 100Kg of enclosure, shields and SQUID amplifiers at 1K. In this paper we review some of the lessons from operating a dry dilution fridge at the JCMT and the necessary changes that have been incorporated. We present the performance of the fridge and discus its role in ensuring the success of SCUBA-2.
SCUBA-2 is a revolutionary 10,000 pixel wide-field submillimetre camera, recently commissioned and now operational
at the James Clerk Maxwell Telescope (JCMT). Twin focal planes each consist of four 32 by 40 sub-arrays of
superconducting Transition Edge Sensor (TES) bolometers, the largest combined low temperature bolometer arrays in
operation, to provide simultaneous imaging at wavelengths of 450 and 850 microns. SCUBA-2 was designed to map
large areas of sky more than 100 times faster than the original ground breaking SCUBA instrument and has achieved this
goal. In this paper we describe the performance of the instrument and present results of characterising the eight science
grade TES bolometer arrays. We discuss the steps taken to optimise the setup of the TES arrays to maximise mapping
speed and show how critical changes to the sub-array module thermal design, the introduction of independent focal plane
and 1K temperature control and enhancements to the cryogenics have combined to significantly improve the overall
performance of the instrument.
SCUBA-2 is a state of the art 10,000 pixel submillimeter camera installed and being commissioned at the James Clerk
Maxwell Telescope (JCMT) providing wide-field simultaneous imaging at wavelengths of 450 and 850 microns. At each
wavelength there are four 32 by 40 sub-arrays of superconducting Transition Edge Sensor (TES) bolometers, each
packaged with inline SQUID multiplexed readout and amplifier. In this paper we present the results of characterising
individual 1280 bolometer science grade sub-arrays, both in a dedicated 50mk dilution refrigerator test facility and in the
instrument installed at the JCMT.
Over preceding conferences, the design and implementation of the SCUBA-2 (Sub-millimeter Common-User
Bolometric Array 2) instrument hardware has been described in detail. SCUBA-2 has been installed on the James Clerk
Maxwell Telescope (JCMT) for over two years and its hardware has been successfully commissioned. This paper
describes the culmination of this process and compares the optical/mechanical design and test expectations of the
instrument hardware against the performance achieved in the field.
Commissioning of SCUBA-2 included a program of skydips and observations of calibration sources intended to
be folded into regular observing as standard methods of source flux calibration and to monitor the atmospheric
opacity and stability. During commissioning, it was found that these methods could also be utilised to characterise
the fundamental instrument response to sky noise and astronomical signals. Novel techniques for analysing onsky
performance and atmospheric conditions are presented, along with results from the calibration observations
SCUBA-2 is a new wide-field submillimeter continuum instrument being commissioned on the James Clerk
Maxwell Telescope on Mauna Kea in Hawaii. SCUBA-2 uses large-scale arrays of superconducting bolometers
with SQUID- (superconducting quantum interference device) based multiplexing and amplification. The sensitivity
of the devices that compose the detector arrays to magnetic fields is such that magnetic shielding, consisting
of superconducting and high-permeability materials, was fitted to the detector enclosure at 1 K to reduce the
magnetic field strength at the focal plane. This paper describes the design and construction of the cryogenic
shielding, and presents verification measurements. The shielding performance was found to meet the instrument
requirements, and compared well to the modelled results.
SCUBA-2 is a new wide-field submillimeter continuum instrument being commissioned on 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. The arrays are
cooled to less than 100 mK by the mixing chamber of a dilution refrigerator (DR), with a radiation shield at a
nominal temperature of 1 K cooled by the DR still. The DR is a "dry" system, using a pulse tube cooler for
precooling of the circulating helium in place of a liquid helium bath. This paper presents key performance data
for the DR.
The detector arrays for the SCUBA-2 instrument consist of TES bolometers with superconducting amplifier and
multiplexing circuits based on Superconducting Quantum Interference Devices (SQUIDs). The SCUBA-2 TES arrays
and their multiplexed SQUID readouts need to be set-up carefully to achieve correct performance. Algorithms have been
developed and implemented based on the first available commissioning grade detector, enabling the array to be set up
and optimized automatically.
The large submillimeter telescope (LST) is a proposed wide-field, 30m-class telescope operating from a ground-based site in the relatively unexplored 0.2 - 1mm waveband. The telescope will be equipped with imaging and spectroscopic instrumentation to allow astronomers to probe the earliest evolutionary stages of galaxies, stars and planets. It is intended to operate the telescope in the 200μm atmospheric window, giving access to unique science; probing the peak emission from the cosmic far-IR/submm background and proto-stellar cores. The wide field-of-view and superb image fidelity will be perfect for large-scale surveys of the sky, such as entire giant molecular clouds and of fields of dusty galaxies at early epochs. It will therefore be an ideal complement to new generation interferometers (such as ALMA). In this paper we present an update on the science case and outline initial designs for both the telescope and instrumentation.
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.
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.
We describe the scientific case and design challenges for an innovative large submillimetre telescope (LST). LST is proposed to have a diameter of at least 30m, operate in the wavelength range from 0.2 - 1mm and will have a wide field-of-view. The submillimetre region allows us to probe objects during formation - i.e. the earliest evolutionary stages of galaxies, stars and planets. Being so close to the peak of the cosmic far-IR/submm background and the emission from proto-stellar cores, the 200μm atmospheric window gives access to unique science. The key advantage of LST over other facilities will be in terms of addressing astronomical questions requiring large fields and good angular resolution: such as surveys of entire giant molecular clouds and fields of dusty galaxies at early epochs. For example, such a telescope would resolve all protoplanetary disks out to 100pc, revolutionising our knowledge of star and planet formation, and detect tens of millions of dusty high-redshift galaxies yielding information on formation and evolution of the early universe. Equipped with a state-of-the-art large format bolometer camera, LST would offer a survey (mapping) speed up to 5,000 times that of ALMA, arcsecond resolution at the shortest wavelengths, point-source sensitivities at least 25 times better than any planned submm facility, and confusion limits 10 times lower than any existing single-aperture telescope. The wide-field-of-view and superb image fidelity available from a single-dish will be perfect for large-scale surveys of the submillimetre sky - an ideal complement to new generation interferometers such as ALMA.
SCUBA-2 is a second generation, wide-field submillimetre camera under development for the James Clerk Maxwell Telescope. With over 12,000 pixels, in two arrays, SCUBA-2 will map the submillimetre sky up to 1000 times faster than the current SCUBA instrument to the same signal-to-noise. Many areas of astronomy will benefit from such a highly sensitive survey instrument: from studies of galaxy formation and evolution in the early Universe to understanding star and planet formation in our own Galaxy. Due to be operational in 2006, SCUBA-2 will also act as a "pathfinder" for the new generation of submillimetre interferometers (such as ALMA) by performing large-area surveys to an unprecedented depth. The baseline design, projected telescope performance and scientific impact of SCUBA-2 are discussed in the paper.
SCUBA-2 is a second generation, wide-field submillimeter camera under development for the James Clerk Maxwell Telescope. With over 12,000 pixels, in two arrays, SCUBA-2 will map the submillimeter sky ~1000 times faster than the current SCUBA instrument to the same signal-to-noise. Many areas of astronomy will benefit from such a highly sensitive survey instrument: from studies of galaxy formation and evolution in the early Universe to understanding star and planet formation in our own Galaxy. Due to be operational in 2006, SCUBA-2 will also act as a "pathfinder" for the new generation of submillimeter interferometers (such as ALMA) by performing large-area surveys to an unprecedented depth. The challenge of developing the detectors and multiplexer is discussed in this paper.
This paper presents a science case for a wide-field camera operating at submillimetre wavelengths on an optical/infrared 100m Overwhelmingly Large Telescope (OWL). Such an instrument (dubbed "SCOWL" - a Submillimetre Camera for OWL) would offer an unprecedented simultaneous high angular resolution and imaging speed, and play a pivotal role in the future of submillimetre astronomy. Other proposed and existing facilities have either coarse resolution (current single dishes) or are relatively inefficient at carrying out large-scale survey work on a reasonable time scale (interferometers). Furthermore, if OWL is located at a dry high-altitude site, SCOWL will be able to exploit the relatively unexplored 200 and 350μm atmospheric windows with unparalleled efficiency. This is the regime where the emission from cold unevolved sources is at its peak, and is thus of unique scientific interest. By observing in the submillimetre, OWL will produce detailed, unbiased views of objects in formation, ranging from Solar-neighbourhood pre-stellar cores to proto-elliptical galaxies in the early Universe.
The Submillimeter Common-User Bolometer Array (SCUBA) is a new continuum camera operating on the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii. It consists of two arrays of bolometric detectors; a 91 pixel 350/450 micron array and a 37 pixel 750/850 micron array. Both arrays can be used simultaneously and have a field-of-view of approximately 2.4 arcminutes in diameter on the sky. Ideally, performance should be limited solely by the photon noise from the sky background at all wavelengths of operation. However, observations at submillimeter wavelengths are hampered by 'sky-noise' which is caused by spatial and temporal fluctuations in the emissivity of the atmosphere above the telescope. These variations occur in atmospheric cells that are larger than the array diameter, and so it is expected that the resultant noise will be correlated across the array and, possibly, at different wavelengths. In this paper, we describe our initial investigations into the presence of sky-noise for all the SCUBA observing modes, and explain our current technique for removing it from the data.
The Submillimeter Common-User Bolometer Array (SCUBA) is one of a new generation of cameras designed to operate in the submillimeter waveband. The instrument has a wide wavelength range covering all the atmospheric transmission windows between 300 and 2000 micrometer. In the heart of the instrument are two arrays of bolometers optimized for the short (350/450 micrometer) and long (750/850 micrometer) wavelength ends of the submillimeter spectrum. The two arrays can be used simultaneously, giving a unique dual-wavelength capability, and have a 2.3 arc-minute field of view on the sky. Background-limited performance is achieved by cooling the arrays to below 100 mK. SCUBA has now been in active service for over a year, and has already made substantial breakthroughs in many areas of astronomy. In this paper we present an overview of the performance of SCUBA during the commissioning phase on the James Clerk Maxwell Telescope (JCMT).
We describe the design and manufacture of SCUBA, which is undergoing laboratory testing prior to commissioning on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. It contains two arrays, one of 91 pixels optimised for 450 micrometers and the second of 37 pixels optimised for 850 micrometers in close-packed arrays, with each pixel having diffraction-limited angular resolution. Some of the original design features of the instrument are described: the cryogenic system operating at 100mK; the optical layout; bolometer manufacture; and array integration. We illustrate the performance of the instrument with test results obtained during the laboratory commissioning.