The enhanced x-ray timing and polarimetry mission (eXTP) is a flagship observatory for x-ray timing, spectroscopy and polarimetry developed by an international consortium. Thanks to its very large collecting area, good spectral resolution and unprecedented polarimetry capabilities, eXTP will explore the properties of matter and the propagation of light in the most extreme conditions found in the universe. eXTP will, in addition, be a powerful x-ray observatory. The mission will continuously monitor the x-ray sky, and will enable multi-wavelength and multi-messenger studies. The mission is currently in phase B, which will be completed in the middle of 2022.
The eXTP (enhanced x-ray timing and polarimetry) mission is a major project of the Chinese Academy of Sciences (CAS), with a large involvement of Europe. The scientific payload of eXTP includes four instruments: the SFA (spectroscopy focusing array) and the PFA (polarimetry focusing array)—led by China —the LAD (large area detector) and the WFM (wide field monitor)—led by Europe (Italy and Spain). They offer a unique simultaneous wide-band x-ray timing and polarimetry sensitivity. The WFM is a wide field x-ray monitor instrument in the 2-50 keV energy range, consisting of an array of six coded mask cameras with a field of view of 180°x90° at an angular resolution of 5 arcmin and four silicon drift detectors in each camera. Its unprecedented combination of large field of view and imaging down to 2 keV will allow eXTP to make important discoveries of the variable and transient x-ray sky and is essential in detecting transient black holes, that are part of the primary science goals of eXTP, so that they can be promptly followed up with other instruments on eXTP and elsewhere.
One of the four instruments on the Chinese-European enhanced x-ray timing polarimetry (eXTP) mission is the wide field monitor (WFM), consisting of six coded aperture cameras. The detector plane of each camera is comprised of four 7x7 cm2 silicon drift detectors assembled with similarly sized hybrid circuit board that contain the front-end electronics (FEE) to read out the detectors. The whole assembly needs to be positioned and kept stable within ~50 micron to guarantee the scientific performance of the WFM. The FEE will have analogue ASICs to perform the read-out process. These bare dies are connected to the detector anode output pads. The detector cathodes need to be provided with voltages down to−1300V. Electrical connections between detector, ASICs and FEE are made by bond wires. The hybrid circuit board is a thick film circuit based on 96% Al2O3 which has a coefficient of thermal expansion that is sufficiently close to that of the silicon detector to avoid misalignment due to the large variations in temperature (−50/+60 °C) during assembly and flight. All materials, components and manufacturing processes will have to be without technology originating from the USA. For eXTP’s phase B, we are developing a demonstration model. For this, an early generation ASIC (‘IDeF-X HDBD’) is employed as well as some components that are US-made but for which there is path to European alternatives. The FEE manufacture and the assembly is already completely non-US. We outline the detector/electronics assembly and discuss the main challenges involved.
The Heterodyne Receiver for Origins (HERO) is the first detailed study of a heterodyne focal plane array receiver for space applications. HERO gives the Origins Space Telescope the capability to observe at very high spectral resolution (R = 107) over an unprecedentedly large far-infrared (FIR) wavelengths range (111 to 617 μm) with high sensitivity, with simultaneous dual polarization and dual-frequency band operation. The design is based on prior successful heterodyne receivers, such as Heterodyne Instrument for the Far-Infrared /Herschel, but surpasses it by one to two orders of magnitude by exploiting the latest technological developments. Innovative components are used to keep the required satellite resources low and thus allowing for the first time a convincing design of a large format heterodyne array receiver for space. HERO on Origins is a unique tool to explore the FIR universe and extends the enormous potential of submillimeter astronomical spectroscopy into new areas of astronomical research.
We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.
The Origins Space Telescope (OST) is a NASA study for a large satellite mission to be submitted to the 2020 Decadal Review. The proposed satellite has a fleet of instruments including the HEterodyne Receivers for OST (HERO). HERO is designed around the quest to follow the trail of water from the ISM to disks around protostars and planets. HERO will perform high-spectral resolution measurements with 2x9 pixel focal plane arrays at any frequency between 468GHz to 2,700GHz (617 to 111 μm). HERO builds on the successful Herschel/HIFI heritage, as well as recent technological innovations, allowing it to surpass any prior heterodyne instrument in terms of sensitivity and spectral coverage.
We present an update on the overall construction progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now that all the major fabrication contracts are in place. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been effected to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project has experienced some delays in procurement and now has first light expected for the middle of 2019.
MATISSE is the mid-infrared interferometric spectrograph and imager for ESO’s Very Large Telescope Interferometer (VLTI). A core mechanism inside the Cold Optical bench is the photometric slider, that enables the choice of observation with or without photometric beams which is achieved by sliding in 4 mirrors or 4 beam splitters into the four telescope beams. To achieve the stringent requirements on beam precision -which asks for mounting pad differences of order of 1 micrometer- all optical components were mounted on a single body and one lapped surface. Test results on the final instrument showed behavior significantly outside specification suggesting contact point height differences up to 6 micrometer. Also repeatability was non-compliant. We will present the cause analysis, the suspected culprit, unsuspected side effects and the implementation of the final solution which lead to a photometric slider well within specification.
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.
MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 μm, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with the four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we remind the concept, the instrumental design, and the main features of MATISSE. We also describe the last months of preparation, the status of the instrument, which was shipped to Cerro Paranal on the site of the ESO Very Large Telescope in October 2017, and the expected schedule for the opening to the community. The instrument is currently in its Commissioning phase. A complementary dedicated article details the Commissioning results, which include the first performance estimates on sky.
We present a solution to the challenges of interfacing the ELT’s METIS to the telescope using a steerable hexapod structure. To guide the architectural choices, lumped physical models were derived from inverse kinematics in order to address the load distribution in each arm. Complete FE Analysis is carried on the optimal solutions of these models. The hexapod arms, which are high precision heavy duty linear actuators enduring forces in the excess of 30 tons, are designed using standard components whenever possible. An overall fully functional support structure design, satisfying the ESO/ELT and METIS requirements, is described.
MIRI ('Mid InfraRed Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength range under development for the James Webb Space Telescope JWST. The flight acceptance tests of the Spectrometer Main Optics flight models (SMO), part of the MIRI spectrometer, are completed in the summer of 2008 and the system is delivered to the MIRI-JWST consortium.
The two SMO arms contain 14 mirrors and form the MIRI optical system together with 12 selectable gratings on grating wheels. The entire system operates at a temperature of 7 Kelvin and is designed on the basis of a 'no adjustments' philosophy. This means that the optical alignment precision depends strongly on the design, tolerance analysis and detailed knowledge of the manufacturing process. Because in principle no corrections are needed after assembly, continuous tracking of the alignment performance during the design and manufacturing phases is important.
The flight hardware is inspected with respect to performance parameters like alignment and image quality. The stability of these parameters is investigated after exposure to various vibration levels and successive cryogenic cool downs. This paper describes the philosophy behind the acceptance tests, the chosen test strategy and reports the results of these tests. In addition the paper covers the design of the optical test setup, focusing on the simulation of the optical interfaces of the SMO. Also the relation to the SMO qualification and verification program is addressed.
To achieve superb stability in cryogenic optical systems, NOVA-ASTRON generally designs optical instruments on the basis of a 'no adjustments' philosophy. This means that in principle no corrections are possible after assembly. The alignment precision and consequently the performance of the instrument is guaranteed from the design, the tolerance analysis and the detailed knowledge of the material behavior and manufacturing process. This resulted in a higher degree of integrated optomechanical-cryogenic design with fewer parts, but with a higher part complexity. The 'no adjustments' strategy is successful because in the end the risk on instrument performance and project delays is much reduced. Astronomical instrument specifications have become more challenging over the years. Recent designs of the European Southern Observatory Very Large Telescope Interferometer (ESO VLTI) 4 Telescope combiner MATISSE include hundreds of optical components in a cryogenic environment. Despite the large number of optical components the alignment accuracy and stability requirements are in the order of nanometers. The 'no adjustments' philosophy would be too costly in this case, because all components would need to meet extremely tight manufacturing specifications. These specifications can be relaxed dramatically if cryogenic mechanisms are used for alignment. Several mechanisms have been developed: a tip-tilt mirror mechanism, an optical path distance mechanism, a slider mechanism, a bistable cryogenic shutter and a mirror mounting clip. Key aspects of these mechanisms are that the optical element and mechanism are combined in a compact single component, driven by e.g. self braking piezo actuators in order to hold position without power. The design, realization and test results of several mechanisms are presented in this paper.
NOVA is involved in the development and realization of various optical astronomical instruments for groundbased as well as space telescopes, with a focus on nearand mid-infrared instrumentation. NOVA has developed a suite of scientific instruments with cryogenic optics for the ESO VLT and VLTI instruments: VISIR, MIDI, the SPIFFI 2Kcamera for SINFONI, X-shooter and MATISSE. Other projects include the cryogenic optics for MIRI for the James Webb Space Telescope and several E-ELT instruments.
Mounting optics is always a compromise between firmly fixing the optics and preventing stresses within the optics. The fixing should ensure mechanical stability and thus accurate positioning in various gravity orientations, temperature ranges, during launch, transport or earthquake. On the other hand, the fixings can induce deformations and sometimes birefringence in the optics and thus cause optical errors. Even cracking or breaking of the optics is a risk, especially when using brittle infrared optical materials at the cryogenic temperatures required in instruments for infrared astronomy, where differential expansion of various materials amounts easily to several millimeters per meter. Special kinematic mounts are therefore needed to ensure both accurate positioning and low stress.
This paper concentrates on the opto-mechanical design of optics mountings, especially for large transmission optics in cryogenic circumstances in space instruments. It describes the development of temperature-invariant (“a-thermal”) kinematic designs, their implementation in ground based instrumentation and ways to make them suitable for space instruments.
METIS is one the first three instruments on the E-ELT. Apart from diffraction limited imaging, METIS will provide coronagraphy and medium resolution slit spectroscopy over the 3 – 19μm range, as well as high resolution (R ~ 100,000) integral field spectroscopy from 2.9 – 5.3μm, including a mode with extended instantaneous wavelength coverage. The unique combination of these observing capabilities, makes METIS the ideal instrument for the study of circumstellar disks and exoplanets, among many other science areas. In this paper we provide an update of the relevant science drivers, the METIS observing modes, the status of the simulator and the data analysis. We discuss the preliminary design of the optical system, which is driven by the need to calibrate observations at thermal IR wavelengths on a six-mirror ELT. We present the expected adaptive optics performance and the measures taken to enable high contrast imaging. We describe the opto-mechanical system, the location of METIS on the Nasmyth instrument platform, and conclude with an update on critical subsystem components, such as the immersed grating and the focal plane detectors. In summary, the work on METIS has taken off well and is on track for first light in 2025.
METIS is the Mid-infrared E-ELT Imager and Spectrograph, which will provide outstanding observing capabilities, focusing on high angular and spectral resolution. It consists of two diffraction-limited imagers operating in the LM and NQ bands respectively and an IFU fed diffraction-limited high-resolution (R=100,000) LM band spectrograph. These science subsystems are preceded by the common fore optics (CFO), which provides the following essential functionalities: calibration, chopping, image de-rotation, thermal background and stray light reduction. We show the evolution of the CFO optical design from the conceptual design to the preliminary optical design, detail the optimization steps and discuss the necessary trade-offs.
We present the Final Design of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), together with a status update on the details of manufacturing, integration and the overall project schedule now that all the major fabrication contracts are in place. We also present a summary of the current planning behind the 5-year initial phase of survey operations. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000. The project is now in the manufacturing and integration phase with first light expected for early of 2018.
MATISSE is the second-generation mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric instrument will allow significant advances by opening new avenues in various fundamental research fields: studying the planet-forming region of disks around young stellar objects, understanding the surface structures and mass loss phenomena affecting evolved stars, and probing the environments of black holes in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the spectral domain of current optical interferometers by offering the L and M bands in addition to the N band. This will open a wide wavelength domain, ranging from 2.8 to 13 μm, exploring angular scales as small as 3 mas (L band) / 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared imaging - closure-phase aperture-synthesis imaging - with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE will offer a spectral resolution range from R ∼ 30 to R ∼ 5000. Here, we present one of the main science objectives, the study of protoplanetary disks, that has driven the instrument design and motivated several VLTI upgrades (GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performances. We also discuss the current status of the MATISSE instrument, which is entering its testing phase, and the foreseen schedule for the next two years that will lead to the first light at Paranal.
FAME is a four-year project and part of the OPTICON/FP7 program that is aimed at providing a breakthrough component for future compact, wide field, high resolution imagers or spectrographs, based on both Freeform technology, and the flexibility and versatility of active systems.
Due to the opening of a new parameter space in optical design, Freeform Optics are a revolution in imaging systems for a broad range of applications from high tech cameras to astronomy, via earth observation systems, drones and defense. Freeform mirrors are defined by a non-rotational symmetry of the surface shape, and the fact that the surface shape cannot be simply described by conicoids extensions, or off-axis conicoids. An extreme freeform surface is a significantly challenging optical surface, especially for UV/VIS/NIR diffraction limited instruments.
The aim of the FAME effort is to use an extreme freeform mirror with standard optics in order to propose an integrated system solution for use in future instruments. The work done so far concentrated on identification of compact, fast, widefield optical designs working in the visible, with diffraction limited performance; optimization of the number of required actuators and their layout; the design of an active array to manipulate the face sheet, as well as the actuator design.
In this paper we present the status of the demonstrator development, with focus on the different building blocks: an extreme freeform thin face sheet, the active array, a highly controllable thermal actuator array, and the metrology and control system.
KEYWORDS: Active optics, Mirrors, Disk lasers, Polishing, Actuators, Monochromatic aberrations, Active optics, Mirrors, Polishing, Interfaces, Chemical elements, Finite element methods, Freeform optics
We present two ways to generate or compensate for first order optical aberrations using smart warping harnesses. In these cases, we used the same methodology leading to replace a previous actuation system currently on-sky and to get a freeform mirror intended to a demonstrator. Starting from specifications, a warping harness is designed, followed by a meshing model in the finite elements software. For the two projects, two different ways of astigmatism generation are presented. The first one, on the VLT-SPHERE instrument, with a single actuator, is able to generate a nearly pure astigmatism via a rotating motorization. Two actuators are sufficient to produce the same aberration for the active freeform mirror, main part of the OPTICON-FAME project, in order to use stress-polishing method.
FAME (Freeform Active Mirror Experiment - part of the FP7 OPTICON/FP7 development programme) intends to demonstrate the huge potential of active mirrors and freeform optical surfaces. Freeform active surfaces can help to address the new challenges of next generation astronomical instruments, which are bigger, more complex and have tighter specifications than their predecessors.
The FAME design consists of a pre-formed, deformable thin mirror sheet with an active support system. The thin face sheet provides a close to final surface shape with very high surface quality. The active array provides the support, and through actuation, the control to achieve final surface shape accuracy.
In this paper the development path, trade-offs and demonstrator design of the FAME active array is presented. The key step in the development process of the active array is the design of the mechanical structure and especially the optimization of the actuation node positions, where the actuator force is transmitted to the thin mirror sheet. This is crucial for the final performance of the mirror where the aim is to achieve an accurate surface shape, with low residual (high order) errors using the minimum number of actuators. These activities are based on the coupling of optical and mechanical engineering, using analytical and numerical methods, which results in an active array with optimized node positions and surface shape.
MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) will be a mid-infrared spectro-interferometer
combining the beams of up to four telescopes of the European Southern Observatory Very Large Telescope
Interferometer (ESO VLTI), providing phase closure and image reconstruction. MATISSE will produce interferometric
spectra in the LM and N band (2.8 to 13 micron).
Building the cryogenic interferometer section of an instrument like MATISSE is inherently complex. During the
preliminary design phase it became clear that this inherent complexity should not be seen as a hurdle but rather a tool; to
keep project risks low it is vital to first comprehend the complexity and second to distribute these complexities to areas
of expertise, i.e. fields of low risk.
With this approach one prevents the typical reaction of either steering away from complexity or digging narrow and deep
to find only a local solution. Complexity can be used to achieve the project goals with a reduced overall project risk. For
example two alternative options: either a complex single structure with limited interfaces or an assembly of many
simpler parts with, in total, much more interfaces. Although simpler in approach, the latter would be a burden on the
overall tolerance chain, assembly procedures, logistics & overall cost, culminating in a higher overall risk to the project;
the unintended shift of complexity and risk to a later project phase. In addition, this fragmentation would reduce the
overall grip on the project and would make it more difficult to identify showstoppers early on. And solving these
becomes exponentially more difficult in later project stages.
The integral multidisciplinary approach, earlier discussed in “MATISSE cold optics opto-mechanical design” Proc. SPIE
7734, 77341S (2010), enables optimal distribution of complexity and lowering of overall project risk. This current
proceeding presents the way in which the high level of opto-mechanical complexity and risks were distributed and dealt
with during the MATISSE Cold Optics Bench instrument development.
Within Infra-Red large wavelength bandwidth instruments the use of mechanisms for selection of observation modes,
filters, dispersing elements, pinholes or slits is inevitable. The cryogenic operating environment poses several challenges
to these cryogenic mechanisms; like differential thermal shrinkage, physical property change of materials, limited use of
lubrication, high feature density, limited space etc.
MATISSE the mid-infrared interferometric spectrograph and imager for ESO's VLT interferometer (VLTI) at Paranal in
Chile coherently combines the light from 4 telescopes. Within the Cold Optics Bench (COB) of MATISSE two concepts
of selection mechanisms can be distinguished based on the same design principles: linear selection mechanisms (sliders)
and rotating selection mechanisms (wheels).Both sliders and wheels are used at a temperature of 38 Kelvin.
The selection mechanisms have to provide high accuracy and repeatability. The sliders/wheels have integrated tracks
that run on small, accurately located, spring loaded precision bearings. Special indents are used for selection of the
slider/wheel position. For maximum accuracy/repeatability the guiding/selection system is separated from the actuation
in this case a cryogenic actuator inside the cryostat.
The paper discusses the detailed design of the mechanisms and the final realization for the MATISSE COB. Limited
lifetime and performance tests determine accuracy, warm and cold and the reliability/wear during life of the instrument.
The test results and further improvements to the mechanisms are discussed.
In this paper we present the design of freeform mirror based optical systems that have the potential to be used in future
astronomical instrumentation in the era of extremely large ground based telescopes. Firstly we describe the optical
requirements followed by a summary of the optimization methodology used to design the freeform surface. The intention
is to create optical architectures, which not only have the numerous advantages of freeform based systems (increased
optical performance and/or reduction of mass and volume), but also can be manufactured and tested with today’s
manufacturing techniques and technologies.
The team plans to build a demonstrator based on one of the optical design examples presented in this paper. The
demonstrator will be built and tested as part of the OPTICON FP7 Freeform Active Mirror Experiment (FAME) project.
A hydroforming technique developed as part of the previous OPTICON FP7 project will be used to produce an accurate,
compact and stable freeform mirror. The manufacturing issues normally experienced in the production of freeform
mirrors are solved through the hydroforming of thin polished substrates, which then will be supported with an active
array structure. The active array will be used to compensate for residual manufacturing errors, thermo-elastic
deformation and gravity-induced errors.
KEYWORDS: Mirrors, Actuators, Disk lasers, Optics manufacturing, Astronomy, Freeform optics, Finite element methods, Active optics, Control systems, Optical design
This paper discusses the development of a demonstrator freeform active mirror for future
astronomical instruments both on Earth and in space. It consists of a system overview and progress
in various areas of technology in the building blocks of the mirror: an extreme freeform thin face
sheet, an active array, design tools and the metrology and control of the system. The demonstrator
aims to investigate the applicability of the technique in high end astronomical systems, also for space
and cryogenically.
MATISSE is the second-generation mid-infrared interferometric spectrograph and imager for ESO’s Very Large
Telescope Interferometer (VLTI). NOVA-ASTRON is responsible for the Cold Optics Bench (COB), representing the
last part of the optics train where the four beams are re-arranged, spectrally dispersed and combined.
The COB consist of two sister units, one for the LM-band, one for the N-band, which were successively completed at
NOVA-ASTRON in autumn 2013 and spring 2014. The LM-band COB is under cryogenic test in its cryostat at
MPIA/Heidelberg; the N-band COB finished cryogenic tests and has been installed at OCA/Nice for integration together
with the Warm Optics. This paper focuses on the manufacturing, integration and test results of the COBs, and gives an overview of the current status.
MATISSE is the mid-infrared spectrograph and imager for the Very Large Telescope Interferometer (VLTI) at Paranal. This second generation interferometry instrument will open new avenues in the exploration of our Universe. Mid-infrared interferometry with MATISSE will allow significant advances in various fundamental research fields: studies of disks around young stellar objects where planets form and evolve, surface structures and mass loss of stars in late evolutionary stages, and the environments of black holes in active galactic nuclei. MATISSE is a unique instrument. As a first breakthrough it will enlarge the spectral domain used by optical interferometry by offering the L & M bands in addition to the N band, opening a wide wavelength domain, ranging from 2.8 to 13 μm on angular scales of 3 mas (L/M band) / 10 mas (N band). As a second breakthrough, it will allow mid-infrared imaging – closure-phase aperture-synthesis imaging – with up to four Unit Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. MATISSE will offer various ranges of spectral resolution between R~30 to ~5000. In this article, we present some of the main science objectives that have driven the instrument design. We introduce the physical concept of MATISSE including a description of the signal on the detectors and an evaluation of the expected performance and discuss the project status. The operations concept will be detailed in a more specific future article, illustrating the observing templates operating the instrument, the data reduction and analysis, and the image reconstruction software.
KEYWORDS: Actuators, Mirrors, Disk lasers, Finite element methods, Freeform optics, Monochromatic aberrations, 3D modeling, Optical spheres, Optics manufacturing, Active optics
In this paper a status report is given on the development of the FAME (Freeform Active Mirror Experiment) active array.
Further information regarding this project can be found in the paper by Venema et al. (this conference). Freeform optics
provide the opportunity to drastically reduce the complexity of the future optical instruments. In order to produce these
non-axisymmetric freeform optics with up to 1 mm deviation from the best fit sphere, it is necessary to come up with
new design and manufacturing methods. The way we would like to create novel freeform optics is by fine tuning a preformed
high surface-quality thin mirror using an array which is actively controlled by actuators. In the following we
introduce the tools deployed to create and assess the individual designs. The result is an active array having optimal
number and lay-out of actuators.
The advent of extremely large telescopes will bring unprecedented light-collecting power and spatial resolution, but it will also lead to a significant increase in the size and complexity of focal-plane instruments. The use of freeform mirrors could drastically reduce the number of components in optical systems. Currently, manufacturing issues limit the common use of freeform mirrors at short wavelengths. This article outlines the use of freeform mirrors in astronomical instruments with a description of two efficient freeform optical systems. A new manufacturing method is presented which seeks to overcome the manufacturing issues through hydroforming of thin polished substrates. A specific design of an active array is detailed, which will compensate for residual manufacturing errors, thermoelastic deformation, and gravity-induced errors during observations. The combined hydroformed mirror and the active array comprise the Freeform Active Mirror Experiment, which will produce an accurate, compact, and stable freeform optics dedicated to visible and near-infrared observations.
Methods are presented that can be used to design and operate optical systems with actively controlled components.
Optical systems based on extreme aspheres and freeform surfaces have been investigated. Existing three mirror
anastigmat (TMA) designs have been re-optimized in order to achieve two spherical and one challenging (extreme
asphere or freeform) mirror surface. We foresee a manufacturing method, where the mirror substrate is plasticised by
cold hydro-forming and its surface shape can be controlled via actuators to remove residual errors. Based on singular
value decomposition (SVD) and regularization of the sensitivity matrix, the degrees of freedom (DOF) of the active
surface can be analysed. Phase diversity (PD) is used as a wavefront retrieval process, to measure the performance metric
and determine the sensitivity matrix thus correlating the performance metric of the system and the DOF of the active
component.
Throughout the history of telescopes and astronomical instrumentation, new ways were found to open up unexplored
possibilities in fundamental astronomical research by increasing the telescope size and instrumentation complexity. The
ever demanding requirements on instrument performance pushes instrument complexity to the edge. In order to take the
next leap forward in instrument development the optical design freedom needs to be increased drastically. The use of
more complex and more accurate optics allows for shorter optical trains with smaller sizes, smaller number of
components and reduced fabrication and alignment verification time and costs.
Current optics fabrication is limited in surface form complexity and/or accuracy. Traditional active and adaptive optics
lack the needed intrinsic long term stability and simplicity in design, manufacturing, verification and control. This paper
explains how and why active arrays literally provide a flexible but stable basis for the next generation optical
instruments. Combing active arrays with optically high quality face sheets more complex and accurate optical surface
forms can be provided including extreme a-spherical (freeform) surfaces and thus allow for optical train optimization and
even instrument reconfiguration. A zero based design strategy is adopted for the development of the active arrays
addressing fundamental issues in opto-mechanical engineering. The various choices are investigated by prototypes and
Finite Element Analysis. Finally an engineering concept will be presented following a highly stable adjustment strategy
allowing simple verification and control. The Optimization metrology is described in an additional paper for this
conference by T. Agócs et al.
The increasing requirement on the performance of optical instruments leads to more complex optical systems including
active optical components. The role of these components is to correct for environmental influences on the instrument and
reduce manufacturing and alignment residuals. We describe a method that can be used to design and operate instruments
with active components that are not necessarily located in the pupil. After the optical system is designed, the next step is
to analyse the available degrees of freedom (DOF), select the best set and include them in the active component. By
performing singular value decomposition (SVD) and regularization of the sensitivity matrix, the most efficient DOF for
the active component can be calculated. In operation of the instrument, the wavefront at the pupil plane is reconstructed
from phase diversity (PD); a metrology having minimal impact on instrument design. Information from SVD, forward
and reverse optimization are used to model the process, explore the parameter space and acquire knowledge on
convergence. The results are presented for a specific problem.
MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) will be a mid-infrared spectro-interferometer
combining the beams of up to four telescopes of the European Southern Observatory Very Large Telescope
Interferometer (ESO VLTI), providing phase closure and image reconstruction. MATISSE will produce interferometric
spectra in the LM and in the N band (3.0 to 13.0 micron) and is as such a successor of MIDI. Beams pass the warm preoptics
and in the cold optics all beams recombine on the detector where they create a spectral interference pattern.
Instruments with a large wavelength bandwidth like MATISSE usually comprise mechanisms for selection of
observation mode, filters, dispersing elements, pinholes or slits. The cryogenic operating environment poses several
challenges to these cryogenic mechanisms like differential thermal shrinkage, physical property change of materials and
lubrication. For the MATISSE instrument two concepts of selection mechanisms can be distinguished: linear selection
mechanisms (sliders) and rotating selection mechanisms (wheels). Both mechanisms provide high accuracy and
repeatability. The feature density is high in a limited space envelope. Cryogenic electric motors are used as the actuator
for all these mechanisms. This paper describes the design and realization of these linear and rotating selection
mechanisms.
MATISSE is a mid-infrared spectro-interferometer combining the beams of up to four Unit Telescopes or Auxiliary
Telescopes of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory.
MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. New characteristics present in
MATISSE will give access to the mapping and the distribution of the material, the gas and essentially the dust, in the
circumstellar environments by using the mid-infrared band coverage extended to L, M and N spectral bands. The four
beam combination of MATISSE provides an efficient uv-coverage: 6 visibility points are measured in one set and 4
closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.
We give an overview of the instrument including the expected performances and a view of the Science Case. We present
how the instrument would be operated. The project involves the collaborations of several agencies and institutes: the
Observatoire de la Côte d’Azur of Nice and the INSU-CNRS in Paris, the Max Planck Institut für Astronomie of
Heidelberg; the University of Leiden and the NOVA-ASTRON Institute of Dwingeloo, the Max Planck Institut für
Radioastronomie of Bonn, the Institut für Theoretische Physik und Astrophysik of Kiel, the Vienna University and the
Konkoly Observatory.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. The Flight Model development of the Spectrometer Main Optics (SMO)
consisted of small design changes to improve optical performance, structural (dynamic) behaviour and integration based
on the experience and verification results of the previous Qualification and Verification models. A full test program was
performed in order to keep test efforts at the higher MIRI level as small as possible. The flight model underwent full
optical as well as mechanical qualification testing. In December 2008 the SMO was shipped, after successful integration
and verification, for final integration within the MIRI instrument.
This paper will describe the Flight Model improvements (based on the Qualification and Verification Model test results),
the problems and issues encountered during integration and verification and the verification test results.
MATISSE is a mid-infrared spectro-interferometer combining beams of up to four telescopes of the ESO VLTI providing phase closure and image reconstruction using interferometric spectra in the LM and N band. This paper presents the opto-mechanical design of the two cold benches containing several types of cryogenic mechanisms (shutter,
Tip/Tilt) used for cryogenic alignment. Key aspects are detailed such as the highly integrated opto-mechanical approach
of the design in order to guarantee component stability and accuracy specifications in the order of nanometers and arcseconds.
METIS: "Mid-infrared ELT Imager and Spectrograph" is the mid-infrared (3 - 14 microns) instrument for imaging and
spectroscopy for the European Extremely Large Telescope (E-ELT). To ensure high detection sensitivity the internal
radiation of the instrument needs to be eliminated (sufficiently reduced) and thus needs to be operated at cryogenic
temperatures.
The instrument is divided in a cold and warm system. The cold system, the actual heart of the system, is subdivided into
five main opto-mechanical modules located within a common cryostat (part of the warm system). The warm system
provides the crucial environment for the cold system, including the instrument control and maintenance equipment. The
end 2009 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 Netherlands (PI: Bernhard Brandl - NOVA),
Germany, France, United Kingdom and Belgium. During this conference various aspects of the METIS instrument
(design) are presented in several papers, including the instrument concept and science case, and the system engineering
and optical design.
This paper describes the design constraints and key issues regarding the packaging of this complex cryogenic instrument.
The design solutions to create a light, small and fully accessible instrument are discussed together with the specific
subdivision of the cold and warm system to ensure concurrent development at various different institutes around Europe.
In addition the paper addresses the design and development studies for the special, challenging units such as the large
optical image de-rotator, the (2D) chopper mechanism and the special cryogenic drives.
MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very
Large Telescope Interferometer (VLTI) of the European Southern Observatory. The related science case study
demonstrates the enormous capability of a new generation mid-infrared beam combiner.
MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. MIDI is a very successful
instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in
MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar
environments by using a wide mid-infrared band coverage extended to L, M and N spectral bands. The four beam
combination of MATISSE provides an efficient UV-coverage : 6 visibility points are measured in one set and 4 closure
phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.
ASTRON is involved in the development and realization of various optical astronomical instruments for ground-based as
well as space telescopes, with a focus on near- and mid-infrared instrumentation. ASTRON has developed, among
others, cryogenic optics for the first generation ESO VLT and VLTI instruments VISIR, MIDI and the SPIFFI 2K-camera
for SINFONI. Currently under construction are MIRI for the James Webb Space Telescope and X-shooter for the
second generation ESO VLT instrumentation, while the initial design of several ELT instruments has started.
Mounting optics is always a compromise between firmly fixing the optics and preventing stresses within the optics. The
fixing should ensure mechanical stability and thus accurate positioning in various gravity orientations, temperature
ranges, during launch, transport or earthquake. On the other hand, the fixings can induce deformations and sometimes
birefringence in the optics and thus cause optical errors. Even cracking or breaking of the optics is a risk, especially at
the cryogenic temperatures required in instruments for infrared astronomy, where differential expansion of various
materials amounts easily to several millimetres per meter. Special kinematic mounts are therefore needed to ensure both
accurate positioning and low stress.
Though ASTRON is involved in the full realization of instruments from initial design to commissioning, this paper
concentrates on the opto-mechanical design of optics mountings, especially for large transmission optics in cryogenic
circumstances. It describes the development of temperature-invariant ("a-thermal"), kinematic designs and how they are
implemented in instruments such as SPIFFI and X-shooter.
This paper presents the specifications, design, construction and evaluation of a piezo-driven tip/tilt/focus mechanism
which can align a detector or any other optical component in a cryogenic environment. Even with a no-adjustment design
philosophy, usually one or two components have to be adjusted in order to compensate for the total of optical and
mechanical tolerances in an optical cryogenic instrument. Normally these adjustments are made by means of shims or
stiff screw mechanisms and are applied at room temperature. In order to adjust the particular component(s), mostly by
just a few microns, the high-risk and time-consuming operation of opening a cryostat is required. For a large cryostat the
typical cycle of cooling, testing, warm-up, opening, adjustment, closing and cooling again, takes roughly two weeks.
Often the cycle needs to be repeated a few times before the required position is obtained. ASTRON developed a piezo
driven tip/tilt/focus mechanism which can adjust a detector or any other optical component in both the ambient and
cryogenic (<100 K, vacuum) environment. Only during adjustment the system is active, for the rest of time it is a passive
robust system with a high stability. The main specifications are a stroke of ± 0,6 mm and tip/tilt of ±1,2 mrad.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. The Spectrometer Main Optics (SMO) system has been designed on the basis of
a 'no adjustments' philosophy. This means that the optical alignment precision depends strongly on the design, tolerance
analysis and detailed knowledge of the manufacturing process. Because in principle no corrections are possible after
assembly, continuous tracking of the alignment performance during the design and manufacturing phases is important.
This is done by controlling the "alignment budget" which allows a detailed comparison of the required and achieved
alignment from component to system level. This paper will describe the development of the SMO alignment budget, and
how it is used to bring the alignment performance under control. In addition, we will discuss the results of the actual
alignment measurements on the SMO hardware and the feedback of these results into the alignment budget.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. In March 2007 the qualification and verification phase of the Spectrometer Main
Optics (SMO), part of the MIRI spectrometer came to an end. In this phase it is shown that the SMO subsystem can
provide the necessary performance and withstand the harsh environments of a launch and outer space. In this phase
different models of the SMO have been inspected with respect to performance parameters like alignment and image
quality and have been exposed to vibration tests and successive cryogenic cool downs. This paper will describe the
philosophy behind the verification plan, the chosen test strategy and reports the results of these tests. In addition the
paper covers the design of the optical test setup, focusing on the simulation of the optical interfaces of the SMO.
Since the start of the design efforts in 2003, the design of the Optical Bench Assembly for MIRI is detailed and finalized. MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the mid infrared under development for the James Webb Space Telescope. MIRI is developed by a combined European-US Consortium. As part of this consortium, ASTRON develops the Spectrometer Main Optics Working in such a large international
consortium requires focus on traceability of requirements, design, interface and verification data. This is achieved using
several systems engineering practices like requirement analyses and allocation, technical performance management and configuration management. These processes are tailored to the complexity and scale of the project. The paper summarizes these practices and provides examples of the tailoring process and system engineering tools used.
In December 2004 the European Consortium that develops the optical bench assembly for MIRI successfully passed the Preliminary Design Review. MIRI is the combined imager and integral field spectrometer for the 5-28 micron wavelength range under development for the JWST. After this PDR milestone the optical design of the MIRI spectrometer is now implemented in a compact, modular mechanical design that puts all optical elements in place within the required tolerances. Many aspects of this design are based on the heritage of previous instruments developed at ASTRON, in particular the cryogenic optics for the mid-IR VLT instruments VISIR and MIDI, but several adjustments
to this design philosophy were made to develop the necessary space-qualified light-weighted components. Prototyping of these components has now started. This paper describes trade-offs and solutions for the opto-mechanical design of the optics (gratings, mirrors and their mountings) and of the main structure of the spectrometer, taking into account optical performance, manufacturability, cost and lead times. It also addresses the complex interface management in a large international consortium and reports first prototype results.
KEYWORDS: James Webb Space Telescope, Spectroscopy, Mirrors, Sensors, Electronics, Imaging systems, Optical components, Mid-IR, Optical filters, Picture Archiving and Communication System
MIRI is one of three focal plane instruments for the JWST covering the wavelengths region 5...28 μm. It is jointly developed by US and European institutes with the latter ones being responsible for the complete optical bench assembly, cryomechanisms, calibration source and the related electronics. MIRI is the combination of an imager with coronographic and low-resolution spectroscopic capabilities and a high-resolution integral-field spectrometer. These diverse options require several mechanisms to select a specific observing mode: (1) a filter wheel with bandpass filters, coronographic masks and a prism, (2) two grating/dichroic wheels with dispersing and order-sorting elements and (3) a flip mirror to direct the beam of an internal black body source into the spectrometer section. All mechanisms are required to operate under laboratory conditions (warm launch) as well as in the cryovacuum in space. The heat dissipation has to be small and the reliability and precision very high. Our low risk approach is the application of successfully qualified and flown components of the ISOPHOT (ISO) and PACS (HERSCHEL) instruments. We will report on the concept developed in phase B.
In this paper, we present the status of VISIR, the mid-infrared instrument to be installed in 2003 at the Cassegrain focus of MELIPAL, one of the four 8-meter telescopes of the European Very Large Telescope. This cryogenic instrument, optimized for diffraction-limited performance in both mid-infrared atmospheric windows (N and Q band), combines imaging capabilities over a field up to about 1x1 arcmin2, and long-slit (0.5 arcmin) grating spectroscopy with various spectral resolutions up to R=25000 at 10 μm and 12500 at 20 μm. The contract to design and build VISIR was signed in November 1996 between the European Southern Observatory (ESO) and a French-Dutch consortium of institutes led by Service d'Astrophysique of Commissariat l'Energie Atomique (CEA). A key step in the project has been passed in December 2001, with the first infrared images in the laboratory and in April 2002 with the first infrared spectra in the laboratory. We present the results of the laboratory tests of the instrument, which is scheduled to be shipped to Paranal at the end of 2002.
Mechanisms operating in the cryovacuum are required to rotate filter and dichroic wheels, to tilt gratings and to flip in the beam of an internal calibration source. The design proposed here is based on similar mechanisms flown successfully on the liquid helium cooled European ISO-satellite and being presently under qualification for ESA's cooled HERSCHEL-satellite. Their main characteristics are high reliability during the 10 year lifetime in space, high precision and low heat dissipation in the cryovacuum.
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