The Canary Hosted Upgrade for High-Order Adaptive Optics is an experimental test-bench for high-order SCAO, in R-and I-bands, designed to utilize the Canary experiment at the 4.2m William Herschel Telescope. Chough consists of a pick-off that diverts light from after the 2nd DM in Canary up onto a custom breadboard which hosts the Chough sub-systems. These consist primarily of a ADC, an optical relay, a 1020-actuator DM, a 31 x 31 SH-WFS, and finally a Science Imager. Each of these sub-systems is detailed, with emphasis on interesting and unusual features. As an integrated experiment, the October/2016 on-sky engineering run is first described and then the re-integration of Chough in the laboratory during 2017 as a standalone instrument. In its latter guise, it is a host for additional instrumentation dedicated for high-order AO. An example briefly described is the CAWS interferometer, designed to produce absolute phase residual measurements over a wide chromatic bandwidth (paper #10703-212 in this meeting). We report on consequences of design decisions made for cost reasons, the bench’s fundamental performance, lessons learnt during the various stages of the project so far, and end by describing plans for Chough’s exploitation in the future for high-order SCAO research in the visible and near-IR.
HARMONI is a visible and near-infrared integral field spectrograph equipped with two complementary adaptive optics systems, fully integrated within the instrument. A Single Conjugate AO (SCAO) system offers high performance for a limited sky coverage and a Laser Tomographic AO (LTAO) system provides AO correction with a very high sky-coverage. While the deformable mirror performing real-time correction of the atmospheric disturbances is located within the telescope itself, the instrument contains a suite of state-of-the-art and innovative wavefront sensor systems. Laser guide star sensors (LGSS) are located at the entrance of the instrument and fed by a dichroic beam splitter, while the various natural guide star sensors for LTAO and SCAO are located close to the science focal plane. We present opto-mechanical architecture and design at PDR level for these wavefront sensor systems.
MOSAIC is a mixed-mode multiple object spectrograph planned for the ELT that uses a tiled focal plane to support a variety of observing modes. The MOSAIC AO system uses 4 LGS WFS and up to 4 NGS WFS positioned anywhere within the full 10 arcminute ELT field of view to control either the ELT M4/5 alone for GLAO operation feeding up to 200 targets in the focal plane, or M4/5 in conjunction with 10 open-loop DMs for MOAO correction. In this paper we present the overall design and performance of the MOSAIC GLAO and MOAO systems.
Assembly, Integration, Test and Validation (AIT/V) phases for AO instruments, in laboratory as in the telescope, represent numerous technical challenges. The Laboratoire d’Astrophysique de Marseille (LAM) is in charge of the AIT/V preparation and planning for the MOSAIC (ELT-MOS) instrument, from identification of needs, challenges, risks, to defining the optimal AIT strategy for this highly modular and serialized instrument. In this paper, we present the status of this study and describe several AIT/V scenarios as well as a planning for AIT phases in Europe and in Chile. We also show our capabilities, experience and expertise to lead the instrument MOSAIC AIT/V activities.
The Optical Relay Module of the MOSAIC multiple-object spectrograph is used to relay 400-1800nm light picked off from the ELT focal plane to either a fibre-based integral field unit or a natural guide star wavefront sensor. Here we present the preliminary optical design offering a telecentric exit beam with a focal-ratio of F/17.718 and the opto-mechanical analysis of flexures with a study of the impact in the optical layout performances such as: deviation of the PSF centroid, tip-tilt of the image focal plane, variations of the wavefront error, optical quality and pupil wandering at the deformable mirror position.
Following a successful Phase A study, we introduce the delivered conceptual design of the MOSAIC1 multi-object spectrograph for the ESO Extremely Large Telescope (ELT). MOSAIC will provide R~5000 spectroscopy over the full 460-1800 nm range, with three additional high-resolution bands (R~15000) targeting features of particular interest. MOSAIC will combine three operational modes, enabling integrated-light observations of up to 200 sources on the sky (high-multiplex mode) or spectroscopy of 10 spatially-extended fields via deployable integral-field units: MOAO6 assisted high-definition (HDM) and Visible IFUs (VIFU). We will summarise key features of the sub-systems of the design, e.g. the smart tiled focal-plane for target selection and the multi-object adaptive optics used to correct for atmospheric turbulence, and present the next steps toward the construction phase.
Product Assurance is an essential activity to support the design and construction of complex instruments developed for major scientific programs. The international size of current consortia in astrophysics, the ambitious and challenging developments, make the product assurance issues very important. The objective of this paper is to focus in particular on the application of Product Assurance Activities to a project such as MOSAIC, within an international consortium. The paper will also give a general overview on main product assurance tasks to be implemented during the development from the design study to the validation of the manufacturing, assembly, integration and test (MAIT) process and the delivery of the instrument.
When combined with the huge collecting area of the ELT, MOSAIC will be the most effective and flexible Multi-Object Spectrograph (MOS) facility in the world, having both a high multiplex and a multi-Integral Field Unit (Multi-IFU) capability. It will be the fastest way to spectroscopically follow-up the faintest sources, probing the reionisation epoch, as well as evaluating the evolution of the dwarf mass function over most of the age of the Universe. MOSAIC will be world-leading in generating an inventory of both the dark matter (from realistic rotation curves with MOAO fed NIR IFUs) and the cool to warm-hot gas phases in z=3.5 galactic haloes (with visible wavelenth IFUs). Galactic archaeology and the first massive black holes are additional targets for which MOSAIC will also be revolutionary. MOAO and accurate sky subtraction with fibres have now been demonstrated on sky, removing all low Technical Readiness Level (TRL) items from the instrument. A prompt implementation of MOSAIC is feasible, and indeed could increase the robustness and reduce risk on the ELT, since it does not require diffraction limited adaptive optics performance. Science programmes and survey strategies are currently being investigated by the Consortium, which is also hoping to welcome a few new partners in the next two years.
HiPERCAM is a quintuple-beam imager that saw first light on the 4.2 m William Herschel Telescope (WHT) in October 2017 and on the 10.4 m Gran Telescopio Canarias (GTC) in February 2018. The instrument uses re- imaging optics and 4 dichroic beamsplitters to record ugriz (300–1000 nm) images simultaneously on its five CCD cameras. The detectors in HiPERCAM are frame-transfer devices cooled thermo-electrically to 90°C, thereby allowing both long-exposure, deep imaging of faint targets, as well as high-speed (over 1000 windowed frames per second) imaging of rapidly varying targets. In this paper, we report on the as-built design of HiPERCAM, its first-light performance on the GTC, and some of the planned future enhancements.
An astronomical adaptive optics test-bench, designed to replicate the conditions of a 4 m-class telescope, is presented. Named DRAGON-Next Generation, it is constructed primarily from commercial off-the-shelf components with minimal customization (approximately a 90:10 ratio). This permits an optical design which is modular and this leads to a reconfigurability. DRAGON-NG has been designed for operation for the following modes: (high-order) SCAO, (twin-DM) MOAO, and (twin-DM) MCAO. It is capable of open-loop or closed-loop operation, with (3) natural and (3) laser guide-star emulation at loop rates of up to 200Hz. Field angles of up-to 2.4 arcmin (4m pupil emulation) can pass through the system. The design is dioptric and permits long cable runs to a compact real-time control system which is on-sky compatible. Therefore experimental validation can be carried out on DRAGON-NG before transferring to an on-sky system, which is a significant risk mitigation.
CHOUGH is a small, fast project to provide an experimental on-sky high-order SCAO capability to the 4.2m WHT telescope. The basic goal has r<sub>0</sub>-sized sub- apertures with the aim of achieving high-Strehl ratios (> 0:5) in the visible (> 650 nm). It achieves this by including itself into the CANARY experiment: CHOUGH is mounted as a breadboard and intercepts the beam within CANARY via a periscope. In doing so, it takes advantage of the mature CANARY infrastructure, but add new AO capabilities. The key instruments that CHOUGH brings to CANARY are: an atmospheric dispersion compensator; a 32 × 32 (1000 actuator) MEMS deformable mirror; 31 × 31 wavefront sensor; and a complementary (narrow-field) imager. CANARY provides a 241-actuator DM, tip/tilt mirror, and comprehensive off-sky alignment facility together with a RTC. In this work, we describe the CHOUGH sub-systems: backbone, ADC, MEMS-DM, HOWFS, CAWS, and NFSI.
The CANARY-Hosted Upgrade for High-Order Adaptive Optics (CHOUGH), is a narrow-field of view High- Order Single Conjugate on-sky AO demonstrator to be placed on the 4.2m WHT telescope. It aims to produce a Strehl ratio greater than 0.5 in the visible region of the spectrum (> 640nm). A High-Order wave-front sensor (HOWFS) is a central piece of the experiment; it is a Shack-Hartmann with a sampling of 31x31 subapertures across the pupil. A variable aperture spatial filter designed to reduce aliasing for high-spatial frequencies, located at a focal plane preceding the lenslet array. The HOWFS has a quad-cell configuration on the detector with a one-pixel guard ring and 48<i>μ</i>m subaperture. The detector is a NuVu EMCCD camera, 24<i>μ</i>m pixel size, operating at >500Hz. The lenslet array, collimator and relay are commercial off-the-shelf. This was technically challenging due to the small size of the pupil, 2.3mm, and the small optics involved in the design.
Vertical profiles of the atmospheric optical turbulence strength and velocity is of critical importance for simulating, designing, and operating the next generation of instruments for the European Extremely Large Telescope. Many of these instruments are already well into the design phase meaning these profies are required immediately to ensure they are optimised for the unique conditions likely to be observed. <p> </p>Stereo-SCIDAR is a generalised SCIDAR instrument which is used to characterise the profile of the atmospheric optical turbulence strength and wind velocity using triangulation between two optical binary stars. Stereo-SCIDAR has demonstrated the capability to resolve turbulent layers with the required vertical resolution to support wide-field ELT instrument designs. These high resolution atmospheric parameters are critical for design studies and statistical evaluation of on-sky performance under real conditions. Here we report on the new Stereo-SCIDAR instrument installed on one of the Auxillary Telescope ports of the Very Large Telescope array at Cerro Paranal. Paranal is located approximately 20 km from Cerro Armazones, the site of the E-ELT. Although the surface layer of the turbulence will be different for the two sites due to local geography, the high-altitude resolution profiles of the free atmosphere from this instrument will be the most accurate available for the E-ELT site. <p> </p>In addition, these unbiased and independent profiles are also used to further characterise the site of the VLT. This enables instrument performance calibration, optimisation and data analysis of, for example, the ESO Adaptive Optics facility and the Next Generation Transit Survey. It will also be used to validate atmospheric models for turbulence forecasting. We show early results from the commissioning and address future implications of the results.
ESO have recently revisited the design of the E-ELT with a view to reducing cost, leading to de-scopes which include a
smaller primary aperture and removal of the Gravity Invariant Focal Station (GIFS). In its original concept, the EAGLE
instrument was designed to be located at the GIFS and consequently a major mechanical re-design was required to enable
the instrument to be placed on its side in a conventional straight-through Nasmyth configuration. In this paper, a conceptual
design for a new instrument structure is presented. A preliminary finite element analysis was carried out to assess the
structure’s behaviour under operating loading conditions (e.g. gravity loads). The results of this analysis demonstrate that
the proposed design is viable, without any significant degradation in performance compared to the original GIFS design.
KMOS is a multi-object near-infrared integral field spectrograph built by a consortium of UK and German institutes for
the ESO Paranal Observatory. We report on the on-sky performance verification of KMOS measured during three
commissioning runs on the ESO VLT in 2012/13 and some of the early science results.
The EAGLE instrument is a Multi-Object Adaptive Optics (MOAO) fed, multiple Integral Field Spectrograph (IFS),
working in the Near Infra-Red (NIR), on the European Extremely Large Telescope (E-ELT). A Phase A design study
was delivered to the European Southern Observatory (ESO) leading to a successful review in October 2009. Since that
time there have been a number of developments, which we summarize here. Some of these developments are also
described in more detail in other submissions at this meeting.
The science case for the instrument, while broad, highlighted in particular: understanding the stellar populations of
galaxies in the nearby universe, the observation of the evolution of galaxies during the period of rapid stellar build-up
between redshifts of 2-5, and the search for 'first light' in the universe at redshifts beyond 7. In the last 2 years substantial
progress has been made in these areas, and we have updated our science case to show that EAGLE is still an essential
facility for the E-ELT. This in turn allowed us to revisit the science requirements for the instrument, confirming most of
the original decisions, but with one modification.
The original location considered for the instrument (a gravity invariant focal station) is no longer in the E-ELT
Construction Proposal, and so we have performed some preliminary analyses to show that the instrument can be simply
adapted to work at the E-ELT Nasmyth platform.
Since the delivery of the Phase A documentation, MOAO has been demonstrated on-sky by the CANARY experiment at
the William Herschel Telescope.
KMOS is a multi-object near-infrared integral field spectrograph being built by a consortium of UK and German
institutes. We report on the final integration and test phases of KMOS, and its performance verification, prior to
commissioning on the ESO VLT later this year.
The Centre for Advanced Instrumentation (CfAI) of Durham University (UK) has developed a conceptual design for the
Integral Field Unit (IFU) for EAGLE based on diamond-machined monolithic multi-faceted metal-mirror arrays as an
alternative to the glass IFU which is currently baselined. The CfAI has built up substantial expertise with the design,
manufacture, integration, alignment and acceptance testing of such systems, through the successful development of IFUs
for the Gemini Near-InfraRed Spectrograph (GNIRS) and JWST NIRSpec and 24 IFUs for ESO’s K-band Multi-Object
Spectrometer (KMOS). The unprecedented performance of the KMOS IFUs (Strehl < 0.8 across the field, throughput
rising from 86% at a wavelength of 1 micron to 93% at 2.5 micron) demonstrates that the current state-of-the-art
technology is sufficiently mature to meet the demanding requirements for EAGLE. In addition, the use of monolithic
multi-faceted metal mirror arrays will greatly simplify the manufacture, integration and alignment of such systems thus
potentially reducing technical and programmatic risks and cost. Through the timely completion of the KMOS IFUs,
which required the fabrication of an unprecedented 1152 optical surfaces, the CfAI have demonstrated that they have the
capacity to produce the required volume within reasonable schedule constraints. All the facilities (design, fabrication e.g.
diamond machining, metrology, integration and test) required for the successful realisation of such systems are available
in-house, thus minimising programmatic risks. This paper presents the opto-mechanical design and predicted
performance (based on the actual measured performance of the KMOS IFUs) of the proposed metal IFU.
The Centre for Advanced Instrumentation (CfAI) of Durham University (UK) has recently successfully completed the
development of 24 Integral Field Units (IFUs) for the K-band Multi-Object Spectrometer (KMOS). KMOS is a second
generation instrument for ESO’s Very Large Telescope (VLT) which is due for delivery during the summer of 2012. The
KMOS IFU is based on the Advanced Image Slicer Concept developed by the CfAI and previously successfully
implemented on the Gemini Near-InfraRed Spectrograph and JWST NIRSpec. Each IFU contains 14 channels which
have to be accurately aligned. In addition, all 24 IFUs have to be co-aligned requiring the accurate alignment of an
unprecedented grand total of 1152 optical surfaces. In this paper we describe how this has been achieved through the use
of complex monolithic multi-faceted metal mirror arrays, which were fabricated in-house by means of freeform diamond
machining. We will summarise the results from the metrology performed on each of the optical components and describe
how these were integrated and aligned into the system. We will also summarise the results from the system level
acceptance tests, which demonstrate the excellent performance of the IFUs. Each of the 24 IFUs is essentially diffraction
limited across the entire field (Strehl ratios ~ 0.8) with throughput predictions (based on measurements of the surface
roughness) rising from 86% at a wavelength of 1 micron to 93% at 2.5 micron. We believe that this level of performance
has not previously been achieved in any image slicing IFU and showcases the potential of the current state-of-the-art
XMS is a multi-channel wide-field spectrograph designed for the prime focus of the 3.5m Calar-Alto telescope. The
instrument is composed by four quadrants, each of which contains a spectrograph channel. An innovative mechanical
design -at concept/preliminary stage- has been implemented to: 1) Minimize the separation between the channels to
achieve maximal filling factor; 2) Cope with the very constraining space and mass overall requirements; 3) Achieve very
tight alignment tolerances; 4) Provide lens self-centering under large temperature excursions; 5) Provide masks including
4000 slits (edges thinner than 100μ). An overview of this very challenging mechanical design is here presented.
Two feasibility studies for spectrographs that can deliver at least 4000 MOS slits over a 1° field at the prime focuses of
the Anglo-Australian and Calar Alto Observatories have been completed. We describe the design and science case of the
Calar Alto eXtreme Multiplex Spectrograph (XMS) for which an extended study, half way between feasibility study and
phase-A, was made. The optical design is quite similar than in the AAO study for the Next Generation 1 degree Field
(NG1dF) but the mechanical design of XMS is quite different and much more developed. In a single night, 25000 galaxy
redshifts can be measured to z~0.7 and beyond for measuring the Baryon Acoustic Oscillation (BAO) scale and many
other science goals. This may provide a low-cost alternative to WFMOS for example and other large fibre spectrographs.
The design features four cloned spectrographs which gives a smaller total weight and length than a unique spectrograph
to makes it placable at prime focus. The clones use a transparent design including a grism in which all optics are about
the size or smaller than the clone rectangular subfield so that they can be tightly packed with little gaps between
subfields. Only low cost glasses are used; the variations in chromatic aberrations between bands are compensated by
changing a box containing the grism and two adjacent lenses. Three bands cover the 420nm to 920nm wavelength range
at 10A resolution while another cover the Calcium triplet at 3A. An optional box does imaging. We however also studied
different innovative methods for acquisition without imaging. A special mask changing mechanism was also designed to
compensate for the lack of space around the focal plane. Conceptual designs for larger projects (AAT 2º field, CFHT,
VISTA) have also been done.
KMOS is a near-infrared multi-object integral-field spectrometer which is one of a suite of second-generation
instruments under construction for the VLT. The instrument is being built by a consortium of UK and German
institutes working in partnership with ESO and is now in the manufacture, integration and test phase. In this paper
we present an overview of recent progress with the design and build of KMOS and present the first results from the
subsystem test and integration.
The KBand Multi-Object Spectrograph (KMOS) is an astronomical spectrograph designed for integration with the VLT
(Very Large Telescope) and capable of surveying 24 independent fields. The IFU (Integral Field Unit) subsystem is a
complex instrument with no less than 1080 optical surfaces. We focus here on the design of the manufacturing and test
process for this subsystem. Design of this system is based on experience gained on similar complex optical systems, such
as the NIRSPEC (Near Infra Red Spectrometer) IFU that will be integrated into the James Webb Space Telescope.
Surfaces are produced in aluminium using a freeform diamond machine. Many surfaces are multi-faceted and of
complex form. The requirement for 15 nm RMS form accuracy poses a significant challenge for the machining process.
In particular, the large number of highly complex surfaces represents the most serious design challenge. Design of the
part fixturing is critical to the consistent achievement of the required surface accuracy. Furthermore, efficient test
procedures must be developed to characterise all surfaces. In recognition of this, particular emphasis is placed on the
metrology of these components. Moreover, the volume of complex metrology involved offers a unique opportunity to
fully characterise and optimise the manufacturing process.
The heart of the KMOS instrument is a complex optical system with over 300 separate optical paths. The optical design
is spread between 4 sub-systems which have been designed at three different institutions. In order that the end to end
performance of the final design can be monitored and controlled it is necessary to specify the performance and interface
requirements of each sub-system clearly.
This paper describes the parameters that were necessary to control so that the sub-system designs could be carried out
independently while maintaining visibility and control of the end to end performance. The method of apportioning the
budgets between the sub-systems and the modeling performed to verify compliance is also described.
Durham University's Centre for Advanced Instrumentation (CfAI) are currently prototyping key components for the KMOS and JWST NIRSpec Integral Field Units (IFUs). These next-generation IFUs will make extensive use of complex monolithic multi-faceted metal mirror arrays, which are fabricated by means of freeform diamond machining. Using this technique, the inherent accuracy of the diamond machining equipment is exploited to achieve the required relative alignment accuracy of the facets, as well as obtain the necessary optical surface quality for each individual facet, thus facilitating the integration and subsequent testing of these complex systems. The CfAI have pioneered the use of such arrays in the IFU for the Gemini Near-InfraRed Spectrograph (GNIRS IFU), which was installed at Gemini South in April, 2004. The requirements for the next generation of IFUs, however, demand a considerable improvement in the optical performance of these components, e.g. alignment accuracy of the facets, surface form accuracy and roughness. In our paper we briefly discuss the optical designs of KMOS and JWST NIRSpec IFU, and summarise the requirements on the optical components. We then present details of the diamond machining techniques employed to fabricate these highquality components and discuss the latest results from our prototyping activities, which demonstrate our capability of producing optical components that meet the demanding specifications.
KMOS is a near-infrared multi-object integral field spectrometer which has been selected as one of a suite of second-generation instruments to be constructed for the ESO VLT in Chile. The instrument will be built by a consortium of UK and German institutes working in partnership with ESO and is currently at the end of its preliminary design phase. We present the design status of KMOS and discuss the most novel technical aspects and the compliance with the technical specification.
Durham University's Centre for Advanced Instrumentation (CfAI) have developed a technique for fabricating monolithic multi-faceted mirror arrays using freeform diamond machining. Using this technique, the inherent accuracy of the diamond machining equipment is exploited to achieve the required relative alignment accuracy of the facets, as well as an excellent optical surface quality for each individual facet. Monolithic arrays manufactured using this technique, have been successfully applied in the Integral Field Unit for the GEMINI Near-InfraRed Spectrograph (GNIRS IFU), which was recently commissioned at GEMINI South. In this paper, we present details of the fabrication process and optical performance of these components. We will also briefly discuss how their implementation has facilitated the GNIRS IFU's opto-mechanical system design and subsequent integration and test, and highlight the resulting improvement in
Optical designs of fore-optics and Advanced Image Slicer (AIS) systems made for the second generation VLT instruments KMOS1 and MUSE2,3 conceptual design studies are presented. KMOS is an infrared multi-integral-field spectrograph with 24 fields, each 2.8" x 2.8" with a 0.2" resolution, patrolling a 7' field. The described optics of KMOS are the fore-optics, from the images given by the pickoff system to the slicers, and the slicer systems themselves. The study also includes a derotator design in case the instrument would have been too heavy to be attached to the telescope. MUSE is an integral field spectrograph for the 0.465 µm to 1 µm bandwidth with a 1' x 1' field and a resolution of 0.2". Two optical designs were proposed, one mostly transmissive which is now the baseline, the other mostly using reflective optics. The later is described in this paper. It includes a derotator, an atmospheric dispersion corrector, a transmissive removable magnifier, a transmissive field splitter that cut the field in 24 subfields, the relay optics of each subfield to each slicer and the slicer systems. While MUSE is for the visible and would then in principle need transmissive optics, the use of reflective optics is justified because its minimum wavelength is 0.465 µm; modern reflective coatings give transmission larger than 98% for these wavelengths. We discuss the development of the manufacturing of AIS to extend its application to the visible from its actual use in the IR.
The Astronomical Instrumentation Group (AIG) of the University of Durham has recently completed an integral field unit (IFU) for use on the Gemini-South telescope with the Gemini Near-Infrared Spectrograph (GNIRS) built by the National Optical Astronomy Observatories (NOAO, USA). When the IFU is deployed remotely inside the instrument cryostat, GNIRS is converted into an integral field spectrograph with a field of 5 × 3 arcsec<sup>2</sup> and spatial sampling of 0.15 × 0.15 arcsec<sup>2</sup>, optimised for 1-2.5μm but operable up to 5μm. We present summaries of the design and construction and results from laboratory testing. We also show results obtained at the telescope where a throughput of 90% was measured at 2.5μm, and show that this is consistent with predictions of a simple model where surface scattering is the dominant loss mechanism. The throughput data are well fit by the roughness measured in the laboratory. Finally, we show a few examples of astrophysical data from the commissioning run in April 2004.
Implementation of the optical designs of image slicing Integral Field Systems requires accurate alignment of a large number of small (and therefore difficult to manipulate) optical components. In order to facilitate the integration of these complex systems, the Astronomical Instrumentation Group (AIG) of the University of Durham, in collaboration with the Labor für Mikrozerspanung (Laboratory for Precision Machining - LFM) of the University of Bremen, have developed a technique for fabricating monolithic multi-faceted mirror arrays using freeform diamond machining. Using this
technique, the inherent accuracy of the diamond machining equipment is exploited to achieve the required relative alignment accuracy of the facets, as well as an excellent optical surface quality for each individual facet. Monolithic arrays manufactured using this freeform diamond machining technique were successfully applied in the Integral Field Unit for the GEMINI Near-InfraRed Spectrograph (GNIRS IFU), which was recently installed at GEMINI South. Details of their fabrication process and optical performance are presented in this paper. In addition, the direction of current development work, conducted under the auspices of the Durham Instrumentation R&D Program supported by the UK Particle Physics and Astronomy Research Council (PPARC), will be discussed. The main emphasis of this research is to improve further the optical performance of diamond machined components, as well as to streamline the production and
quality control processes with a view to making this technique suitable for multi-IFU instruments such as KMOS etc., which require series production of large quantities of optical components.
We describe a new concept for an integral field unit that allows the collection of a very large number of spectra. We also describe a complementary low cost spectrograph. Both are necessary for the design of integral field spectrographs with huge numbers of spatial elements. These concepts were developed for the Million Element Integral Field Unit and Spectrograph (MEIFUS) that we are proposing for an 8-m and a larger version for an Extremely Large Telescope (ELT, a 30-m telescope). The 8-m version of this spectrograph would give 2.2 million spectra, each 200 pixels long, covering a field of view of 5.2' x 5.2'. The ELT version would give 1.5 million spectra, each 600 pixels long, with a field of 2.7’ x 3’. The new concept of microslices for integral field units allows us to pack a large number of short spectra tightly on the detector without oversizing the spectrograph. It uses a series of independent cylindrical microlens arrays, as opposed to spherical or "simulated spherical using cylindrical" microlenses. We used the specific characteristics of our instrument, especially the short spectra, to develop a concept of a low cost spectrograph. We show that MEIFUS fills a technological gap between other integral field systems and Fabry-Perot instruments. We believe that integral field spectrographs with such a large number of spatial elements would be too expensive if they were to use fibers, typical slicer systems or typical spectrograph designs.
The Gemini Near IR Spectrograph (GNIRS) currently under development at NOAO and scheduled for delivery in the summer of 2002, will include a powerful and innovative Integral Field Spectroscopy (IFS) capability. The design, integration and test of the GNIRS Integral Field Unit (IFU) are the responsibility of the University of Durham's Astronomical Instrumentation Group. The Critical Design Review is scheduled during the second quarter of the year 2000. Its design is based on the Advanced Image Slicer concept developed as a result of research conducted under the auspices of the Durham Instrumentation R and D Program. A slicer-based system has many advantages over fiber-based designs, especially for cryogenic instruments. The GNIRS IFU consists of two self-contained modules mounted inside the GNIRS slit slide mechanism. This slide mechanism is employed to select the required spectroscopy mode by sliding the respective module into the instrument's optical path. The low resolution option provides a field of view of 3.2 inch X 4.4 inch with a sampling resolution of 0.15 inch over 625 spatial elements and a spectrum length of 1024 pixels, whereas the high resolution optic provides a field of view of 1.0 inch by 1.5 inch with a sampling resolution of 0.04 inch over 972 spatial elements and a spectrum length of 1024 pixels. This paper gives an overview of the IFUs optical design, which has been optimized to take full advantage of the excellent image quality provided by the Gemini telescopes, and the mechanical design.