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.
Ultrafast laser inscription is a versatile manufacturing technique which can be used to modify the refractive index of various glasses on a microscopic scale. This enables the production of a number of photonic devices such as waveguides, beam-splitters, photonic lanterns, and diffraction gratings. In this paper, we report on the use of ultrafast laser inscription to fabricate volume phase transmission gratings in mid-infrared transmitting chalcogenide glass.
We describe the optimisation of the laser inscription process parameters enhancing grating performances via the combination of spectrally resolved grating transmission measurements and theoretical analysis models. The first order diffraction efficiency of the gratings was measured at mid-infrared wavelengths (3-5 μm), and found to exceed 60% at the Littrow blaze wavelength, compared to a substrate external transmittance of 67%. This impressive result implies the diffraction efficiency should exceed 90% for a grating substrate treated with an anti-reflection coating. There is excellent agreement between the modelled grating efficiency and the measured data, and from a least squares fit to the measured data the refractive index modulation achieved during the inscription process is inferred. These encouraging initial results demonstrate that ultrafast laser inscription of chalcogenide glass may provide a potential new and alternative technology for the manufacture of astronomical diffraction gratings for use at near-infrared and mid-infrared wavelengths.
We report on a joint European Science Foundation-ESA “Forward Look” project called TECHBREAK aimed at identifying technological breakthroughs for space originating in the non-space sector. We show how some of the technologies highlighted may impact future space programmes, in particular novel ideas to enable future long-life large telescopes to be deployed. The study’s final report was presented to ESA’s High level Science Policy Advisory Committee (HISPAC) in late 2014. The goals of the study were to forecast the development of breakthrough technologies to enable novel space missions in the 2030-2050 timeframe, and to identify related partnerships through synergies with non-space specialists. It was not prepared to serve as a definitive guide for very specific technologies to be developed for future space missions, but to inform on and flag up the main developments in various technological and scientific areas outside space that may hold promise for use in the space domain. The report does this by identifying the current status of research for each domain, asserting the development horizon for each technology and providing some entry points, in the form of key European experts and institutions with knowledge of the domain. The identification of problems and solutions specific to the space area led us to focus the discussion around the concept of “Overwhelming Drivers” for space research and exploration, i.e. long-term goals that can be transposed into technological development goals. Two of these overwhelming drivers are directly relevant to ambitious future telescope projects, and we will show how some of the technologies we identified such as biomimetic structures, nanophotonics, novel materials and additive manufacturing could be combined to enable revolutionary new concepts for space telescopes.
Due to their high efficiency and broad operational bandwidths, volume phase holographic gratings (VPHGs) are often
the grating technology of choice for astronomical instruments, but current VPHGs exhibit a number of drawbacks
including limits on their size, function and durability due to the manufacturing process. VPHGs are also generally made
using a dichromated gelatine substrate, which exhibits reduced transmission at wavelengths longer than ~2.2 μm,
limiting their ability to operate further into the mid-infrared.
An emerging alternative method of manufacturing volume gratings is ultrafast laser inscription (ULI). This technique
uses focused ultrashort laser pulses to induce a localised refractive index modification inside the bulk of a substrate
material. We have recently demonstrated that ULI can be used to create volume gratings for operation in the visible,
near-infrared and mid-infrared regions by inscribing volume gratings in a chalcogenide glass. The direct-write nature of
ULI may then facilitate the fabrication of gratings which are not restricted in terms of their size and grating profile, as is
currently the case with gelatine based VPHGs.
In this paper, we present our work on the manufacture of volume gratings in gallium lanthanum sulphide (GLS)
chalcogenide glass. The gratings are aimed at efficient operation at wavelengths around 1 μm, and the effect of applying
an anti-reflection coating to the substrate to reduce Fresnel reflections is studied.
A key requirement for astronomical instruments in next generation Extremely Large Telescopes (ELTs) is the
development of large-aperture Integral Field Units (IFUs) that enable the efficient and spatially contiguous sampling of
the telescope image plane for coupling stellar light onto a spectrometer. Current IFUs are complex to fabricate and suffer
from stray light issues, which limits their application in high-contrast studies such as exoplanet imaging. In this paper,
we present our work on the development of freeform microlens arrays using the rapidly maturing technique of ultrafast
laser inscription and selective wet chemical etching. Using the focus spot from a femtosecond laser source as a tool with
an essentially unrestricted “tool-path”, we demonstrate that it is possible to directly write the surface of a lenslet in three
dimensions within the volume of a transparent material. We further show that high surface quality of the lenses can be
achieved by using an oxy-natural gas flame to polish the lens surface roughness that is characteristic of the post-etched
structures. Using our technique, the shape and position of each lenslet can be tailored to match the spatial positioning of
a two-dimensional multimode fiber array, which can be monolithically integrated with the microlens array.
Ultrafast laser inscription (ULI) is a rapidly maturing technique which uses focused ultrashort laser pulses to locally
modify the refractive index of dielectric materials in three-dimensions (3D). Recently, ULI has been applied to the
fabrication of astrophotonic devices such as integrated beam combiners, 3D integrated waveguide fan-outs and
multimode-to-single mode convertors (photonic lanterns). Here, we outline our work on applying ULI to the fabrication
of volume phase gratings (VPGs) in fused silica and gallium lanthanum sulphide (GLS) glasses. The VPGs we fabricated
had a spatial frequency of 333 lines/mm. The optimum fused silica grating was found to exhibit a first order diffraction
efficiency of 40 % at 633 nm, but exhibited approximately 40 % integrated scattered light. The optimum GLS grating
was found to exhibit a first order diffraction efficiency of 71 % at 633 nm and less than 5 % integrated scattered light.
Importantly for future astronomy applications, both gratings survived cooling to 20 K. This paper summarises the grating
design and ULI manufacturing process, and provides details of the diffraction efficiency performance and blaze curves
for the VPGs. In contrast to conventional fabrication technologies, ULI can be used to fabricate VPGs in almost any
dielectric material, including mid-IR transmitting materials such as the GLS glass used here. Furthermore, ULI
potentially provides the freedom to produce complex groove patterns or blazed gratings. For these reasons, we believe
that ULI opens the way towards the development of novel VPGs for future astronomy related applications.
Advances in astronomy are often enabled by adoption of new technology. In some instances this is where the technology
has been invented specifically for astronomy, but more usually it is adopted from another scientific or industrial area of
application. The adoption of new technology typically occurs via one of two processes. The more usual is incremental
progress by a series of small improvements, but occasionally this process is disruptive, where a new technology
completely replaces an older one. One of the activities of the OPTICON Key Technology Network over the past few
years has been a technology forecasting exercise. Here we report on a recent event which focused on the more radical,
potentially disruptive technologies for ground-based, optical and infrared astronomy.
Astrophotonics offers a solution to some of the problems of building instruments for the next generation of telescopes
through the use of photonic devices to miniaturise and simplify instruments. It has already proved its worth in
interferometry over the last decade and is now being applied to nightsky background suppression. Astrophotonics offers
a radically different approach to highly-multiplexed spectroscopy to the benefit of galaxy surveys such as are required to
determine the evolution of the cosmic equation of state. The Astrophotonica Europa partnership funded by the EU via
OPTICON is undertaking a wide-ranging survey of the technological opportunities and their applicability to high-priority
astrophysical goals of the next generation of observatories. Here we summarise some of the conclusions.
The Key Technology Network (KTN) within the OPTICON programme has been developing a roadmap for the
technology needed to meet the challenges of optical and infrared astronomy over the next few years, with particular
emphasis on the requirements of Extremely Large Telescopes. The process and methodology so far will be described,
along with the most recent roadmap.
The roadmap shows the expected progression of ground-based astronomy facilities and the technological developments
which will be required to realise these new facilities. The roadmap highlights the key stages in the development of these
In some areas, such as conventional optics, gradual developments in areas such as light-weighting of optics will slowly
be adopted into future instruments. In other areas, such as large area IR detectors, more rapid progress can be expected as
new processing techniques allow larger and faster arrays. Finally, other areas such as integrated photonics have the
potential to revolutionise astronomical instrumentation.
Future plans are outlined, in particular our intention to look at longer term development and disruptive technologies.
The performance requirements for the next generation of ground-based instruments for optical and infrared astronomy
on current telescopes and future ELTs are generating extreme requirements for stability, for instance to carry out precise
radial velocity measurements, imaging and spectroscopy with high contrast, and diffraction-limited performance at a
level of tens of milliarcsecond. As it is not always possible to make use of a gravity-invariant focal station, flexure must
be accommodated while still minimising thermal loads for cryogenic instruments. Variable thermal loads are another
source of dimensional changes. High stability will require the minimising of the effects of vibration sources, either from
the telescope systems or mechanical coolers. All this must be done while maintaining mass budgets, an especial
challenge for large, wide-field, multi-object spectrographs.
The next generation of large ground-based optical and infrared telescopes will provide new challenges for designers of
astronomical instrumentation. The varied science cases for these extremely large telescopes (ELTs) require a large
range of angular resolutions, from near diffraction-limited performance via correction of atmospheric turbulence using
adaptive optics (AO), to seeing-limited observations. Moreover, the scientific output of the telescopes must also be
optimized with the consideration that, with current technology, AO is relatively ineffective at visible wavelengths, and
that atmospheric conditions will often preclude high-performance AO. This paper explores some of the issues that arise
when designing ELT instrumentation that operates across a range of angular-resolutions and wavelengths. We show
that instruments designed for seeing-limited or seeing-enhanced observations have particular challenges in terms of size
and mass, while diffraction-limited instruments are not as straightforward as might be imagined.
One of the highlights of the European ELT Science Case book is the study of resolved stellar populations, potentially out to the Virgo Cluster of galaxies. A European ELT would enable such studies in a wide range of unexplored, distant environments, in terms of both galaxy morphology and metallicity. As part of a small study, a revised science case has been used to shape the conceptual design of a multi-object, multi-field spectrometer and imager (MOMSI). Here we present an overview of some key science drivers, and how to achieve these with elements such as multiplex, AO-correction, pick-off technology and spectral resolution.
We report on the development of instrument concepts for a European ELT, expanding on studies carried out as part of the ESO OWL concept. A range of instruments were chosen to demonstrate how an ELT could meet or approach the goals generated by the OPTICON science team, and used to push the specifications and requirements of telescope and adaptive optics systems. Preliminary conclusions are presented, along with a plan for further more detailed instrument design and technology developments. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract number 011863).
A key instrument for an Extremely Large Telescope (ELT) is likely to be multi-object spectrometer which observes at least 100 discrete sources with diffraction limited spatial resolution and moderate spectral resolution in the wavelength region from 1.0 to 2.5 μm. Such an instrument has been chosen as the principal driver for the Smart Focal Planes technology development project which has brought together 14 companies and institutes in Europe and Australia. An overview of a new ELT instrument concept based upon beam manipulators (including novel 'starbug' miniature robots) is presented; supported by a summary of scientific goals and systems requirements. Progress made on specific support technology studies is also presented, including work on image slicer replication and cryogenic reconfigurable slits.
A prototype cryogenic 'pick-off' arm for selecting a small field from the focal plane of a large telescope has been built and tested against a set of scientific requirements representative of those for proposed multi-integral-field spectrographs. In this paper, we present the design of the arm and the results of the cryogenic testing. Since the proposed instruments will require tens of arms, perhaps hundreds, we have also considered the industrialisation of the manufacture and assembly of the arms. We briefly discuss this aspect of the design and the possibilities for future instrumentation on Extremely Large Telescopes.
Smart Focal Planes are devices that enable the efficient sampling of a telescope's focal plane to feed spectroscopic and imaging instruments. Examples are integral field units (fiber and image slicers), cryogenic beam manipulators, and MOEMS (micro-opto-electromechanical systems) such as miniature slit shutters. These technologies are critical in making best use of the current 8m class telescopes for key science goals such as spectroscopic surveys of high redshift galaxies, and will be even more important for Extremely Large Telescope (ELT) instruments. In fact, the density of pixels in an ELT focal plane with several milliarcsecond resolution will mean that sub-sampling of the field will be needed even for imaging. We have proposed a joint European project to develop these technologies, building on expertise from partners in the UK, France, the Netherlands, Spain, Germany and others, and led by the UK. We describe the current status of these technologies, showing how they will contribute to the feasibility and performance of proposed instruments for ELTs, and concentrating on capabilities within Europe. We then outline the proposed future developments, highlighting the technical challenges, such as the difficulties of manufacturing and verifying complex image slicers with thousands of optical surfaces, and building highly reliable cryogenic mechanisms such as pick-off arms, beam steering mirrors and reconfigurble slit mechanisms.
We present the results of a detailed technical study of the use of image slicers for multiple integral field spectroscopy at infrared wavelengths. Our solution uses independently controlled robotic arms to relay selected portions of the focal plane to fixed positions where they are dissected using a set of advanced image slicers. We discuss the technical requirements of this approach and describe a feasibility study to examine the risks and technical challenges.
The Beam Steering Mirror (BSM) subsystem is a critical part of the SPIRE Instrument for the ESA Herschel Space Observatory. It is used to steer the beam of the telescope on the photometer and spectrometer arrays in 2 orthogonal directions, for purposes of fully sampling the image, fine pointing and signal modulation.
The UK Astronomy Technology Centre (ATC) is part of a consortium of 15 institutes in Europe and the USA which was formed to build SPIRE and which is lead by Dr M. Griffin of the University of Wales, Cardiff.
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.
A submillimeter continuum array instrument being built for the 15-m James Clerk Maxwell Telescope on Mauna Kea, Hawaii is described. The instrument contains 2 arrays, one of 91 pixels optimized for 438 microns and the second of 37 pixels optimized for 855 microns. Both are hexagonally close-packed, with each pixel having diffraction-limited angular resolution. Conical horns and single-moded waveguides are used to couple to the submillimeter beams, minimizing the bolometer background loading. A filter changing mechanism allows operations of the arrays at 350 and 750 microns. Single 'photometric' pixels are provided optimized for operation at 350, 600, 750, 1100, 1400 and 2000 microns. The instrument will have bolometers sensitive enough to reach the photon-noise sensitivity limit at both wavelengths, corresponding to an optical noise equivalent power (NEP) of 1.6 x 10 to the -16th WHz exp -1/2. This is achieved by cooling to 0.1 K, using a dilution refrigerator.