The Fly's Eye camera system is a multiple-passband full-sky surveying instrument employing 19 wide-field cameras in a mosaic arrangement on a spherical frame. The cameras equipped with fast focal ratio lenses and Sloan filters. The cameras are supported by single mount while the sidereal tracking, i.e. the compensation for the apparent celestial rotation is performed by a hexapod mount. As discussed in our earlier design-related publications, this tracking is unavoidable when considering 0:3 gigapixel imaging, a field-of-view diameter of 120° and exposure times around a few minutes. With this camera system we intend to perform time-domain astronomy and observe several kind of astronomical phenomena based on variability.
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.
In this paper, we detail the manufacturing process for the lenses that will constitute the new two-degree field-of-view Prime Focus Corrector (PFC) for the 4.2m William Herschel Telescope (WHT) optimised for the upcoming WEAVE Multi-Object Spectroscopy (MOS) facility. The corrector, including an Atmospheric Dispersion Corrector (ADC), is made of six large lenses, the largest being 1.1-meter diameter. We describe how the prescriptions of the optical design were translated into manufacturing specifications for the blanks and lenses. We explain how the as-built glass blank parameters were fed back into the optical design and how the specifications for the lenses were subsequently modified. We review the critical issues for the challenging manufacturing process and discuss the trade-offs that were necessary to deliver the lenses while maintaining the optimal optical performance. A short description of the lens optical testing is also presented. Finally, the subsequent manufacturing steps, including assembly, integration, and alignment are outlined.
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.
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.
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.
WEAVE is the next-generation, wide-field, optical spectroscopy facility for the William Herschel Telescope (WHT) in La Palma, Canary Islands, Spain. The WHT will undergo a significant adaptation to accommodate this facility. A two-
degree Prime Focus Corrector (PFC), that includes an Atmospheric Dispersion Compensator, is being planned and is currently in its final design phase. To compensate for the effects of temperature-induced image degradation, the entire PFC system will be translated along the telescope optical axis. The optical system comprises six lenses, the largest of which will have a diameter of 1.1m. Now that the optical elements are in production, the designs for the lens cells and
the mounting arrangements are being analysed to ensure that the image quality of the complete system is better than 1.0 arcsec (80% encircled energy diameter) over the full field of view. The new PFC system is designed to be routinely
interchanged with the existing top-end ring. This will maximise the versatility of the WHT and allow the two top-end
systems to be interchanged as dictated by the scientific needs of the astronomers that will use WEAVE and other
instruments on the telescope. This manuscript describes the work that has been carried out in developing the designs for
the mechanical subsystems and the plans for mounting the lenses to attain an optical performance that is commensurate with the requirements derived from planning the WEAVE surveys.
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 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.
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.
WEAVE is the next-generation optical spectroscopy facility for the William Herschel Telescope and aims at
spectroscopic follow-up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE places in the re-fitted
prime focus either 1000 fibres, 20 fibre-coupled mini-IFUs or a single large 600 fibre IFU. A spectrograph on the
Nasmyth platform analyses the light and supports, in a single exposure, either R~5,000 observations over the full 366-
975 nm wavelength range or simultaneous R~20,000 observations over two out of three pre-specified bands within this
wavelength range. This paper describes the requirements, optical design and mechanical design of the WEAVE
spectrograph.
The Fly's Eye Project is a high resolution, high coverage time-domain survey in multiple optical passbands: our goal is to
cover the entire visible sky above the 30° horizontal altitude with a cadence of ~3 min. Imaging is going to be
performed by 19 wide-field cameras mounted on a hexapod platform resembling a fly’s eye. Using a hexapod developed
and built by our team allows us to create a highly fault-tolerant instrument that uses the sky as a reference to define its
own tracking motion. The virtual axis of the platform is automatically aligned with the Earth’s rotational axis; therefore
the same mechanics can be used independently from the geographical location of the device. Its enclosure makes it
capable of autonomous observing and withstanding harsh environmental conditions. We briefly introduce the electrical,
mechanical and optical design concepts of the instrument and summarize our early results, focusing on sidereal tracking.
Due to the hexapod design and hence the construction is independent from the actual location, it is considerably easier to
build, install and operate a network of such devices around the world.
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.
In order to attain precise, accurate and stateless positioning of telescope mounts we apply microelectromechanical
accelerometer systems (also known as MEMS accelerometers). In common practice, feedback from the mount
position is provided by electronic, optical or magneto-mechanical systems or via real-time astrometric solution
based on the acquired images. Hence, MEMS-based systems are completely independent from these mechanisms.
Our goal is to investigate the advantages and challenges of applying such devices and to reach the sub-arcminute
range { that is well smaller than the field-of-view of conventional imaging telescope systems. We present how
this sub-arcminute accuracy can be achieved with very cheap MEMS sensors. Basically, these sensors yield raw
output within an accuracy of a few degrees. We show what kind of calibration procedures could exploit spherical
and cylindrical constraints between accelerometer output channels in order to achieve the previously mentioned
accuracy level. We also demonstrate how can our implementation be inserted in a telescope control system.
Although this attainable precision is less than both the resolution of telescope mount drive mechanics and the
accuracy of astrometric solutions, the independent nature of attitude determination could significantly increase
the reliability of autonomous or remotely operated astronomical observations.
We present an overview of and status report on the WEAVE next-generation spectroscopy facility for the William
Herschel Telescope (WHT). WEAVE principally targets optical ground-based follow up of upcoming 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
spectrograph, with a pair of 8k(spectral) x 6k (spatial) pixel cameras, 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 final
design and early procurement phase, with commissioning at the telescope expected in 2017.
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.
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.
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.
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.
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