17 research outputs found
Challenges in optics for Extremely Large Telescope instrumentation
We describe and summarize the optical challenges for future instrumentation
for Extremely Large Telescopes (ELTs). Knowing the complex instrumental
requirements is crucial for the successful design of 30-60m aperture
telescopes. After all, the success of ELTs will heavily rely on its
instrumentation and this, in turn, will depend on the ability to produce large
and ultra-precise optical components like light-weight mirrors, aspheric
lenses, segmented filters, and large gratings. New materials and manufacturing
processes are currently under study, both at research institutes and in
industry. In the present paper, we report on its progress with particular
emphasize on volume-phase-holographic gratings, photochromic materials,
sintered silicon-carbide mirrors, ion-beam figuring, ultra-precision surfaces,
and free-form optics. All are promising technologies opening new degrees of
freedom to optical designers. New optronic-mechanical systems will enable
efficient use of the very large focal planes. We also provide exploratory
descriptions of "old" and "new" optical technologies together with suggestions
to instrument designers to overcome some of the challenges placed by ELT
instrumentation.Comment: (Proc. OPTICON Key Technology Network Workshop, Rome 20-21 October
2005
MOONS: a Multi-Object Optical and Near-infrared Spectrograph for the VLT
MOONS is a new conceptual design for a Multi-Object Optical and Near-infrared
Spectrograph for the Very Large Telescope (VLT), selected by ESO for a Phase A
study. The baseline design consists of 1000 fibers deployable over a field of
view of 500 square arcmin, the largest patrol field offered by the Nasmyth
focus at the VLT. The total wavelength coverage is 0.8um-1.8um and two
resolution modes: medium resolution and high resolution. In the medium
resolution mode (R=4,000-6,000) the entire wavelength range 0.8um-1.8um is
observed simultaneously, while the high resolution mode covers simultaneously
three selected spectral regions: one around the CaII triplet (at R=8,000) to
measure radial velocities, and two regions at R=20,000 one in the J-band and
one in the H-band, for detailed measurements of chemical abundances. The grasp
of the 8.2m Very Large Telescope (VLT) combined with the large multiplex and
wavelength coverage of MOONS - extending into the near-IR - will provide the
observational power necessary to study galaxy formation and evolution over the
entire history of the Universe, from our Milky Way, through the redshift desert
and up to the epoch of re-ionization at z>8-9. At the same time, the high
spectral resolution mode will allow astronomers to study chemical abundances of
stars in our Galaxy, in particular in the highly obscured regions of the Bulge,
and provide the necessary follow-up of the Gaia mission. Such characteristics
and versatility make MOONS the long-awaited workhorse near-IR MOS for the VLT,
which will perfectly complement optical spectroscopy performed by FLAMES and
VIMOS.Comment: 9 pages, 5 figures. To appear in the proceedings of the SPIE
Astronomical Instrumentation + Telescopes conference, Amsterdam, 201
Freeform diamond machining of complex monolithic metal optics for integral field systems
Dimensional metrology of mirror segments for extremely large telescopes
Metrology is critical amongst the challenges associated with the production of mirror segments on the scale required by proposed extremely-large telescopes. To achieve the optical specification in a reasonable time requires measurements with an unprecedented combination of accuracy, stability and speed. This study suggests combining several promising methods for use at different stages of production. Pallet mounting is proposed to permit the segments to be handled without significant distortion and to provide fiducials for precise location of the segment. Final qualification of a segment would include comparison with a master reference that had been certified by consensus among a number of independent experts
Millimetre-wave optics design and verification
Microwave background astronomy requires very high performance millimetre-wave optical systems. However, compact quasi-optics are difficult to design with any confidence using techniques developed for visible wavelengths. In this paper we investigate the performance of existing software design tools (ASAP, CODE V, GLAD) as well as a Gaussian beam mode analysis technique not yet available as commercial software. We have devised a set of test cases and used these to study the underlying methodologies and physics of these packages and we look at their ability to analyse millimetre systems and components. We have used GRASP as our benchmark software
Far-infrared optics design and verification
Compact quasi-optics are difficult to design with any confidence using techniques developed for visible wavelengths. In this paper we investigate the performance of existing software design tools (ASAP, CODE V, GLAD) as well as a Gaussian beam mode analysis technique not yet available as commercial software. We have devised a set of test cases and used these to study the underlying methodologies and physics of these packages and we probe their suitability for the analysis of submillimetre-wave systems and components. We have used the physical optics package GRASP as our benchmark software
UFTI : The 0.8-2.5 mu m fast track imager for the UK infrared telescope
In 1996, it was proposed to build a near-infrared imager for the 3.8-m UK Infrared Telescope in Hawaii, to exploit the 1024 pixel format detectors that were then becoming available. In order to achieve a fast delivery, the instrument was kept simple and existing designs were reused or modified where possible. UFTI was delivered within 2.5 years of the project start. The instrument is based around a 1k Rockwell Hawaii detector and a LSR Astrocam controller and uses the new Mauna Kea optimised J,H,K filter set along with I and Z broad-band filters and several narrow-band line filters. The instrument is cooled by a CTI cry-cooler, while the mechanisms are operated by cold, internal, Bergelahr stepping motors. On UKIRT it can be coupled to a Fabry-Perot etalon for tunable narrow-band imaging at K, or a waveplate for imaging polarimetry through 1-2.5mum; the cold analyser is a Barium Borate Wollaston prism. UFTI was designed to take full advantage of the good image quality delivered by UKIRT on conclusion of the upgrades programme, and has a fine scale of 0.09 arcsec/pixel. It is used within the UKIRT observatory environment and was the first instrument integrated into ORAC, the Observatory Reduction and Acquisition Control System. Results obtained during instrument characterisation in the lab and over the last 3 years on UKIRT are presented, along with performance figures. UFTI has now been used on UKIRT for several hundred nights, and aspects of instrument performance are discussed
Euclid imaging channels: from science to system requirements
Euclid is an ESA Cosmic Vision wide-field space mission concept dedicated to the high-precision study of Dark Energy and Dark Matter. The mission relies on two primary cosmological probes: Weak gravitational Lensing (WL) and Baryon Acoustic Oscillations (BAO). The first probe requires the measurement of the shape and photometric redshifts of distant galaxies. The second probe is based on the 3-dimensional distribution of galaxies through spectroscopic redshifts. Additional cosmological probes are also used and include cluster counts, redshift space distortions, the integrated Sachs-Wolfe effect (ISW) and galaxy clustering, which can all be derived from a combination of imaging and spectroscopy. Euclid Imaging Channels Instrument of the Euclid mission is designed to study the weak gravitational lensing cosmological probe. The combined Visible and Near InfraRed imaging channels form the basis of the weak lensing measurements. The VIS channel provides high-precision galaxy shape measurements for the measurement of weak lensing shear. The NIP channel provides the deep NIR multi-band photometry necessary to derive the photometric redshifts and thus a distance estimate for the lensed galaxies. This paper describes the Imaging Channels design driver requirements to reach the challenging science goals and the design that has been studied during the Cosmic Vision Assessment Phase