The Mid-infrared E-ELT Imager and Spectrograph, or METIS, is foreseen as an early instrument for the European
Extremely Large Telescope (E-ELT). A key part of METIS is the Cold Chopper (MCC) which switches the optical beam
between the target and a nearby reference sky during observation for characterization of the fluctuating IR background
signal in post-processing. This paper discusses the development and characterization of the realized MCC demonstrator.
The chopper mirror (Ø64mm) should tip/tilt in 2D with a combined angle of up to 13.6mrad with 1.7μrad stability and
repeatability within 5ms (95% duty cycle at 5Hz) at 80K. As these requirements cannot be met in the presence of friction
or backlash, the mirror is guided by a monolithically integrated flexure mechanism. The angular position is actuated by
three linear actuators and measured by three linear position sensors, resulting in a fast tip, tilt, and focus mirror. Using
the third actuator introduces symmetry, and thus homogeneity in forces and heat flux.
In an earlier paper, Ref. [1], the design of the chopper and the breadboard level testing of the key components were
discussed. Since then, the chopper design has been revised to implement the lessons learned from the breadboard test and
a demonstrator has been realized. This demonstrator has undergone an elaborate test program for characterization and
performance validation in a cryogenic environment, as discussed in this paper.
METIS will be among the first generation of scientific instruments on the E-ELT. Focusing on highest angular
resolution and high spectral resolution, METIS will provide diffraction limited imaging and coronagraphy from 3-14μm
over an 20x20 field of view, as well as integral field spectroscopy at R ~ 100,000 from 2.9-5.3μm. In addition,
METIS provides medium-resolution (R ~ 5000) long slit spectroscopy, and polarimetric measurements at N band. While
the baseline concept has already been discussed at previous conferences, this paper focuses on the significant
developments over the past two years in several areas: The science case has been updated to account for recent progress
in the main science areas circum-stellar disks and the formation of planets, exoplanet detection and characterization,
Solar system formation, massive stars and clusters, and star formation in external galaxies. We discuss the developments
in the adaptive optics (AO) concept for METIS, the telescope interface, and the instrument modelling. Last but not least
we provide an overview of our technology development programs, which ranges from coronagraphic masks, immersed
gratings, and cryogenic beam chopper to novel approaches to mirror polishing, background calibration and cryo-cooling.
These developments have further enhanced the design and technology readiness of METIS to reliably serve as an early
discovery machine on the E-ELT.
We present innovative, immersed grating based optical designs for the SMO (Spectrograph Main Optics) module of the
Mid-infrared E-ELT Imager and Spectrograph, METIS. The immersed grating allows a significant reduction of SMO
volume compared to conventional echelle grating designs, because the diffraction takes place in high refractive index
silicon. Additionally, using novel optimization techniques and technical solutions in silicon micromachining offered by
the semiconductor industry, further improvements can be achieved. We show optical architectures based on compact,
double-pass Three Mirror Anastigmat (TMA) designs, which appear advantageous in terms of one or several of the
following: optical performance, reduction of volume, ease of manufacturing and testing. We explore optical designs,
where the emphasis is put on manufacturability and we investigate optical solutions, where the ultimate goal is the
highest possible optical performance. These novel, silicon immersed grating based design concepts are applicable for
future earth and space based spectrometers.
The optimal performance of an instrument relies critically on accurate performance estimates during its design phase. They need to be modeled to give the science and engineering teams a preview of the performance of the instrument, to guide the design process, to prove the capabilities of the instrument and to prepare science ready software tools before the instrument is operational. METIS, the Mid-infrared E-ELT Imager, is an instrument concept for the E-ELT that covers the thermal infrared wavelengths from 2:9 – 14 μm (L, M and N band). It contains a diffraction limited imager and an integral field high resolution spectrograph. The instrument consists of two independent units, the imager and the spectrograph, and is entirely encased in a cryostat to maintain the stable low temperatures required for good performance at mid-infrared wavelengths. METIS was identified in the instrument roadmap as the third instrument for the E-ELT, after two first light instruments. Because in the mid-infrared the Earth's atmosphere and the telescope mirrors radiate and produce a very high thermal background, it is crucial to develop techniques and mechanisms to measure and reduce this background, to achieve the desired performance of an E-ELT. To demonstrate the capabilities of METIS, years before the actual instrument is built and can be tested, we are developing an end-to-end instrument model, which will simulate the full capacity of METIS. The structure of the model and first results of the performance evaluation are shown.
The ‘Mid-infrared ELT Imager and Spectrograph’ (METIS) will be the third instrument on the European Extremely
Large Telescope (E-ELT). METIS will provide diffraction limited imaging in the atmospheric L/M and N-band from 3
to 14 μm over an 18˝×18˝ field of view, as well as high contrast coronagraphy, medium-resolution (R ≤ 5000) long slit
spectroscopy, and polarimetry. In addition, an integral field spectrograph will provide a spectral resolution of R ~
100,000 at L/M band. Focusing on highest angular resolution and high spectral resolution, METIS will deliver unique
science, in particular in the areas of exo-planets, proto-planetary-disks and high-redshift galaxies, which are illustrated in
this paper. The reduction of the E-ELT aperture size had little impact on the METIS science case. With the recent
positive developments in the area of detectors, the METIS instrument concept has reached a high level of technology
readiness. For some key components (cryogenic chopping mirror, immersed grating, sorption cooler and cryogenic
derotator) a development and test program has been launched successfully.
The ESO Very Large Telescope Adaptive Optics Facility (VLT-AOF) will transform the VLT Unit Telescope 4 to an
Adaptive Telescope. In absence of an intermediate focus before the Adaptive Secondary in this Ritchey–Chrétien type
telescope and in order to reduce the testing and calibration of the system on-sky, ASSIST, The Adaptive Secondary
Setup and Instrument STimulator, was developed. It provides an off-sky testing facility for the ESO AOF and will
provide a full testing environment for three elements of the VLT Adaptive Optics Facility: the Deformable Secondary
Mirror (DSM) and the AO modules for MUSE and HAWK-I (GALACSI and GRAAL). ASSIST was delivered to ESO
Garching, where it was assembled and tested. Currently ASSIST is being integrated with the Deformable Secondary
Mirror, the first step in the full system testing of the two AO systems for the VLT AOF on ASSIST. This paper briefly
reviews the design and properties of ASSIST and reports on the first results of ASSIST in stand-alone mode.
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.
METIS, the Mid-infrared E-ELT Imager and Spectrometer is foreseen to be the third instrument on the European
Extremely Large Telescope (E-ELT) and the only instrument to provide high sensitivity mid-IR imaging and
spectroscopy to the E-ELT.
In order to reach the maximum resolution and sensitivity, an adaptive optics system is required. Since the operational
wavelength of METIS is the longest of all E-ELT instruments and the field is relatively small, the complexity of the AO
system is significantly reduced, both in required speed as well as order of the AO system.
Adaptive Optics has been demonstrated to deliver consistently high performance for the current generation of 6-10 meter
class telescopes at mid-infrared wavelengths, and similar performance is expected for METIS on the E-ELT. But in order
to provide a reliable system on the E-ELT, several effects which have a minor impact on 6-8 meter class telescopes will
need to be investigated for their impact on METIS AO. These effects include refractivity, atmospheric composition
variations, but also the operation in a complex operational environment given by both METIS as well as the E-ELT. In
this paper we describe the scientific requirements on the METIS AO system, the specific issues related to Adaptive
Optics in the mid-IR and expected performance of the METIS AO system on the E-ELT.
The Mid-infrared E-ELT Imager and Spectrograph, or METIS, is foreseen as the third instrument for the European
Extremely Large Telescope (E-ELT). A key part of METIS is the Cold Chopper (MCC) which switches the optical beam
between the target and a nearby reference sky during observation for elimination of the fluctuating IR background signal
in post-processing. This paper discusses the development of the MCC demonstrator.
The chopper mirror (Ø64mm) has to tip/tilt in 2D with a combined angle of up to 13.6mrad with 1.7μrad stability and
repeatability within 5ms (95% duty cycle at 5Hz) at 80K. As these requirements cannot be met in the presence of friction
or backlash, the mirror is guided by a monolithically integrated flexure mechanism. The angular position is actuated by
three linear actuators and measured by three linear position sensors, resulting in a fast tip, tilt, and focus mirror. Using
the third actuator to introduce symmetry, homogeneity in forces and heat flux is obtained.
Both the actuators and the sensors are key components. A voice coil actuator had to be custom designed, to achieve the
required acceleration force within the specified 1W heat load. The requirements for the displacement measurement can
be met with a commercially available, fiber interferometry system. For integration of this system, stray light elimination
is a critical design aspect and retro-reflectors have been used to reflect sufficient power into the fiber at large tip/tilt
angles.
ASSIST, The Adaptive Secondary Setup and Instrument STimulator, is being developed to provide a testing facility for
the ESO Adaptive Optics Facility (AOF). It will allow the off-telescope testing of three elements of the VLT AOF; the
Deformable Secondary Mirror (DSM) and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). The core
of ASSIST consists of a 2-mirror setup (AM1-AM2) allowing the on-axis test of the DSM in interferometric mode.
However, during the initial stages of ASSIST integration, DSM would not be present. This makes the task of aligning
AM1-AM2 to within an accuracy of 0.05mm/1 arcmin rather challenging. A novel technique known as Shack-Hartmann
method has been developed and tested in the lab for this purpose. A Shack Hartmann wavefront sensor will be used to
measure the mis-alignment between AM1-AM2 by recording the coma and astigmatism in the presence of large
spherical aberration introduced because of tilt/decenter of AM2 with respect to AM1. Thereafter, 20 optical components
including lenses, flat mirrors and beam-splitter cubes divided into five sub-assemblies should be aligned to AM1-AM2-
DSM axis which ultimately passes through the mechanical axis of large AMOS rotator.
The testing and verification of ESO Very Large Telescope Adaptive Optics Facility (VLT-AOF) requires new and
innovative techniques to deal with the absence of an intermediate focus on the telescope. ASSIST, The Adaptive
Secondary Setup and Instrument STimulator, was developed to provide a testing facility for the ESO AOF and will allow
off-telescope testing of three elements of the VLT Adaptive Optics Facility; the Deformable Secondary Mirror (DSM)
and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). ASSIST will provide a full testing environment
which includes an interferometric testing mode for the DSM, an
on-axis testing mode with a single wavefront sensor and
full operation testing modes for both the AO systems. Both natural as well as laser guide stars will be simulated under
various asterisms and a realistic turbulent atmosphere will be provided for varying atmospheric conditions. ASSIST
passed its final design review and is now being manufactured, integrated and tested and will be operational in mid 2011,
in time for first testing with the DSM.
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
technologies.
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.
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope (E-ELT). It is designed to
provide imaging and spectroscopic capabilities in the 3μm to 14μm region up to a spectral resolution of 100.000. Here
the technical concept of METIS is described which has been developed based on an elaborated science case which is
presented elsewhere in this conference.
There are five main opto-mechanical modules all integrated into a common cryostat: The fore-optics is re-imaging the
telescope focal plane into the cryostat, including a chopper, an optical de-rotator and an un-dispersed pupil stop. The
imager module provides diffraction limited direct imaging, low-resolution grism spectroscopy, polarimetry and
coronagraphy. The high resolution IFU spectrograph offers a spectral resolution of 100.000 for L- and M-band and
optional 50.000 for the N-band. In addition to the WFS integrated into the E-ELT, there is a METIS internal on-axis
WFS operating at visual wavelengths. Finally, a cold (and an external warm) calibration unit is providing all kinds of
spatial and spectral calibrations capabilities. METIS is planned to be used at one of the direct Nasmyth foci available at
the E-ELT.
This recently finished Phase-A study carried out within the framework of the ESO sponsored E-ELT instrumentation
studies has been performed by an international consortium with institutes from Germany, Netherlands, France, United
Kingdom and Belgium.
We present results of performance modelling for METIS, the Mid-infrared European Extremely Large Telescope
Imager and Spectrograph. Designed by a consortium of NOVA (Netherlands), UK Astronomy Technology Centre
(UK), MPIA Heidelberg (Germany), CEA Saclay (France) and KU Leuven (Belgium), METIS will cover the
atmospheric windows in L, M and N-band and will offer imaging, medium-resolution slit spectroscopy (R~1000-
3000) and high-resolution integral field spectroscopy (R~100,000). Our model uses a detailed set of input
parameters for site characteristics and atmospheric profiles, optical design, thermal background and the most
up-to-date IR detector specifications. We show that METIS will bring an orders-of-magnitude level improvement
in sensitivity and resolution over current ground-based IR facilities, bringing mid-IR sensitivities to the micro-
Jansky regime. As the only proposed E-ELT instrument to cover this entire spectral region, and the only mid-IR
high-resolution integral field unit planned on the ground or in space, METIS will open up a huge discovery space
in IR astronomy in the next decade.
KEYWORDS: Absorption, Spectral resolution, Mid-IR, Spectrographs, Iterated function systems, Astronomy, Current controlled current source, Large telescopes, Imaging spectroscopy, Spectroscopes
METIS is a mid-infrared instrument proposed for the European Extremely Large Telescope. It is designed to provide imaging and spectroscopic capabilities in the 3 - 14 micron region up to a spectral resolution of 100000. One of the novel concepts of METIS is that of a high-resolution integral field spectrograph for a diffraction-limited mid-IR instrument. While this concept has many scientific and operational advantages over a long-slit spectrograph, one drawback is that the spectral resolution changes over the field of view. This has an impact on the procedures to correct for telluric absorption lines imprinted on the science spectra. They are a major obstacle in the quest to maximize spectral fidelity, the ability to distinguish a weak spectral feature from the continuum. The classical technique of division by a standard star spectrum, observed in a single IFS spaxel, cannot simply be applied to all spaxels, because the spectral resolution changes from spaxel to spaxel. Here we present and discuss possible techniques of telluric line correction of METIS IFS spectra, including the application of synthetic model spectra of telluric transmission, to maximize spectral fidelity.
METIS is the 'Mid-infrared ELT Imager and Spectrograph', the only planned thermal/mid-IR instrument for the E-ELT.
METIS will provide diffraction limited imaging in the atmospheric L/M and N-band from 3 - 14 μm over an 18"×18"
field of view (FOV). The imager also includes high contrast coronagraphy and low-resolution (900 ≤ R ≤ 5000) long slit
spectroscopy and polarimetry. In addition, an IFU fed, high resolution spectrograph at L/M band will provide a spectral
resolution of R ~ 100,000 over a 0.4"×1.5" FOV. The adaptive optics (AO) system is relatively simple, and METIS can
reach its full performance with the adaptive correction provided by the telescope - and occasionally even under seeing
limited conditions. On a 42m ELT, METIS will provide state-of-the-art mid-IR performance from the ground. The
science case for METIS is based on proto-planetary disks, characterization of exoplanets, formation of our Solar System,
growth of supermassive black holes, and the dynamics of high-z galaxies. With the focus on highest angular resolution
and highest spectral resolution, METIS is highly complementary to JWST and ALMA. This paper summarizes the
science case for METIS, and describes the instrument concept, performance and operational aspects.
ASSIST: The Adaptive Secondary Setup and Instrument STimulator is the test setup for the verification and calibration
of three elements of the VLT Adaptive Optics Facility.; the Deformable Secondary Mirror (DSM) the AO system for
MUSE and HAWK-I (GALACSI and GRAAL). In the DSM testing mode the DSM will be tested using both
interferometry and fast wave front sensing. In full AO mode, ASSIST will allow testing of the AO systems under
realistic atmospheric conditions and optically equivalent to the conditions on the telescope. ASSIST is nearing its final
design review and in this paper we present the current optical and mechanical design of ASSIST. In this paper we
highlight some of the specific aspects of ASSIST that we are developing for ASSIST.
METIS, the Mid-infrared ELT Imager and Spectrograph (formerly called MIDIR), is a proposed instrument for the
European Extremely Large Telescope (E-ELT), currently undergoing a phase-A study. The study is carried out within
the framework of the ESO-sponsored E-ELT instrumentation studies. METIS will be designed to cover the E-ELT
science needs at wavelengths longward of 3μm, where the thermal background requires different operating schemes. In
this paper we discuss the main science drivers from which the instrument baseline has been derived. Specific emphasis
has been given to observations that require very high spatial and spectral resolution, which can only be achieved with a
ground-based ELT. We also discuss the challenging aspects of background suppression techniques, adaptive optics in
the mid-IR, and telescope site considerations. The METIS instrument baseline includes imaging and spectroscopy at the
atmospheric L, M, and N bands with a possible extension to Q band imaging. Both coronagraphy and polarimetry are
also being considered. However, we note that the concept is still not yet fully consolidated. The METIS studies are
being performed by an international consortium with institutes from the Netherlands, Germany, France, United
Kingdom, and Belgium.
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