The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm). It is composed of three channels, each one containing a telescope.
Two of these channels are high resolution imagers (HRI) at respectively 17.1 nm (HRI-EUV) and 121.6 nm (HRI-Ly∝), each one composed of two off-axis aspherical mirrors. The third channel is a full sun imager (FSI) composed of one single off-axis aspherical mirror and working at 17.1 nm and 30.4 nm alternatively. This paper presents the optical alignment of each telescope.
The alignment process involved a set of Optical Ground Support Equipment (OGSE) such as theodolites, laser tracker, visible-light interferometer as well as a 3D Coordinates Measuring Machine (CMM).
The mirrors orientation have been measured with respect to reference alignment cubes using theodolites. Their positions with respect to reference pins on the instrument optical bench have been measured using the 3D CMM. The mirrors orientations and positions have been adjusted by shimming of the mirrors mount during the alignment process.
After this mechanical alignment, the quality of the wavefront has been checked by interferometric measurements, in an iterative process with the orientation and position adjustment to achieve the required image quality.
The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm) spectral ranges. The development of the EUI instrument has been successfully completed with the optical alignment of its three channels’ telescope, the thermal and mechanical environmental verification, the electrical and software validations, and an end-toend on-ground calibration of the two-units’ flight instrument at the operating wavelengths. The instrument has been delivered and installed on the Solar Orbiter spacecraft, which is now undergoing all preparatory activities before launch.
The Extreme Ultraviolet Imager (EUI) is one of the remote sensing instruments on-board the Solar Orbiter mission. It will provide dual-band full-Sun images of the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm), and high resolution images of the solar disk in both extreme ultraviolet (17.1 nm) and vacuum ultraviolet (Lyman-alpha 121.6 nm). The EUI optical design takes heritage of previous similar instruments. The Full Sun Imager (FSI) channel is a single mirror Herschel design telescope. The two High Resolution Imager (HRI) channels are based on a two-mirror optical refractive scheme, one Ritchey-Chretien and one Gregory optical design for the EUV and the Lyman-alpha channels, respectively. The spectral performances of the EUI channels are obtained thanks to dedicated mirror multilayer coatings and specific band-pass filters. The FSI channel uses a dual-band mirror coating combined with aluminum and zirconium band-pass filters. The HRI channels use optimized band-pass selection mirror coatings combined with aluminum band-pass filters and narrow band interference filters for Lyman-alpha. The optical performances result from accurate mirror manufacturing tolerances and from a two-step alignment procedure. The primary mirrors are first co-aligned. The HRI secondary mirrors and focal planes positions are then adjusted to have an optimum interferometric cavity in each of these two channels. For that purpose a dedicated alignment test setup has been prepared, composed of a dummy focal plane assembly representing the detector position. Before the alignment on the flight optical bench, the overall alignment method has been validated on the Structural and Thermal Model, on a dummy bench using flight spare optics, then on the Qualification Model to be used for the system verification test and qualifications.
The Solar Orbiter mission is composed of ten scientific instruments dedicated to the observation of the Sun’s atmosphere and its heliosphere, taking advantage of an out-of ecliptic orbit and at perihelion reaching a proximity close to 0.28 A.U. On board Solar Orbiter, the Extreme Ultraviolet Imager (EUI) will provide full-Sun image sequences of the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm), and high-resolution image sequences of the solar disk in the extreme ultraviolet (17.1 nm) and in the vacuum ultraviolet (121.6 nm). The EUI concept uses heritage from previous similar extreme ultraviolet instrument. Additional constraints from the specific orbit (thermal and radiation environment, limited telemetry download) however required dedicated technologies to achieve the scientific objectives of the mission. The development phase C of the instrument and its sub-systems has been successfully completed, including thermomechanical and electrical design validations with the Structural Thermal Model (STM) and the Engineering Model (EM). The instrument STM and EM units have been integrated on the respective spacecraft models and will undergo the system level tests. In parallel, the Phase D has been started with the sub-system qualifications and the flight parts manufacturing. The next steps of the EUI development will be the instrument Qualification Model (QM) integration and qualification tests. The Flight Model (FM) instrument activities will then follow with the acceptance tests and calibration campaigns.
The Extreme Ultraviolet Imager (EUI) on-board the Solar Orbiter mission will provide full-sun and high-resolution image sequences of the solar atmosphere at selected spectral emission lines in the extreme and vacuum ultraviolet. After the breadboarding and prototyping activities that focused on key technologies, the EUI project has completed the design phase and has started the final manufacturing of the instrument and its validation. The EUI instrument has successfully passed its Critical Design Review (CDR). The process validated the detailed design of the Optical Bench unit and of its sub-units (entrance baffles, doors, mirrors, camera, and filter wheel mechanisms), and of the Electronic Box unit. In the same timeframe, the Structural and Thermal Model (STM) test campaign of the two units have been achieved, and allowed to correlate the associated mathematical models. The lessons learned from STM and the detailed design served as input to release the manufacturing of the Qualification Model (QM) and of the Flight Model (FM). The QM will serve to qualify the instrument units and sub-units, in advance of the FM acceptance tests and final on-ground calibration.
Since more than 20 years, Laboratoire Charles Fabry and Institut d’Astrophysique Spatiale are involved in development
of the EUV multilayer coating for solar imaging. Previous instruments, such as the SOHO EIT and STEREO EUVI
telescopes, employed the Mo/Si multilayer coatings, which offered at that time the best efficiency and stability. We
present here recent results of the development of highly efficient EUV multilayers coatings at 17.4 nm and 30.4 nm for
the Solar Orbiter mission. New multilayer structures, based on a combination of three materials including aluminum,
have been optimized both theoretically and experimentally. We have succeeded to reduce interfacial roughness of Albased
multilayers down to 0.5 nm via optimization of the multilayer design and the deposition process. The EUV peak
reflectance of Al/Mo/SiC and Al/Mo/B4C multilayer coatings reaches 56% at 17.4 nm, the highest value reported up to
now for this wavelength. We have also optimized specific bi-periodic structures that possess two reflection bands in the
EUV range with high spectral selectivity. The EUV reflectivity of these Al-based dual-band coatings are compared with
the Si/Mo/B4C baseline coating for Solar Orbiter. Since the stability of reflecting multilayer coating is an important issue
for space missions, we have also studied the temporal stability as well as the resistivity of the coatings to thermal cycling
and to proton irradiation. Experimental results confirm that Al/Mo/SiC and Al/Mo/B4C multilayer coatings are good
candidates for the Solar Orbiter EUV imaging telescopes.
We report on further development of reflective multilayer coatings containing aluminum as low absorbing material for the extreme ultra-violet (EUV) applications, in particular for solar physics. Optimizations of the multilayer design and deposition process have allowed us to produce Al-based multilayers having relatively low interface roughness and record EUV reflectances in the range from 17 to 40 nm. The peak reflectance values of 56 % at 17.5 nm, 50 % at around 21 nm, and 42 % at 32 nm were achieved with new three-material multilayers Al/Mo/SiC and Al/Mo/B4C at near-normal incidence. We observe a good temporal stability of optical parameters of the multilayers over the period of 4 years. Moreover, the multilayer structure remains stable upon annealing at 100 °C in air during several weeks. We will discuss the optical properties of more complex Al-based systems with regard to the design of multilayer coatings that reflect more than one wavelength and reject some others within the spectral range from 17 to 40 nm. Such multichannel systems with enhanced reflectance and selectivity would provide a further advance in optical performance and compactness of EUV solar imaging instruments. We will discuss general aspects of design, optimization and fabrication of single- and multi-channel multilayer mirrors made with the use of aluminum. We will present recent results on the EUV reflectivity of multilayer coatings based on the Al/Mo/SiC and Al/Mo/B4C material combinations. Al-based multilayer systems are proposed as optical coatings in EUV telescopes of future space missions and in other EUV applications.
The Solar Orbiter mission will explore the connection between the Sun and its heliosphere, taking advantage of an orbit
approaching the Sun at 0.28 AU. As part of this mission, the Extreme Ultraviolet Imager (EUI) will provide full-sun and
high-resolution image sequences of the solar atmosphere at selected spectral emission lines in the extreme and vacuum
ultraviolet.
To achieve the required scientific performances under the challenging constraints of the Solar Orbiter mission it was
required to further develop existing technologies. As part of this development, and of its maturation of technology
readiness, a set of breadboard and prototypes of critical subsystems have thus been realized to improve the overall
instrument design.
The EUI instrument architecture, its major components and sub-systems are described with their driving constraints and
the expected performances based on the breadboard and prototype results. The instrument verification and qualification
plan will also be discussed. We present the thermal and mechanical model validation, the instrument test campaign with
the structural-thermal model (STM), followed by the other instrument models in advance of the flight instrument
manufacturing and AIT campaign.
Phase-locked operation of an array of ten diode lasers is demonstrated in an extended-cavity using the Talbot self-imaging
effect. An output power up to 1.7 W has been obtained. The extracavity coherent conversion of the multilobed
array supermode into a Gaussian mode is investigated theoretically based on a binary phase grating. The best
configuration results in a conversion efficiency of 83%. Experimentally, the conversion efficiency reaches 50% and is
limited by the imperfect coherence of the laser array. We conclude that the conversion setup provides an actual
measurement of the power in the selected array supermode.
During the development of the laser megajoule (LMJ), a high power laser facility dedicated to DT fusion, CEA has made
important efforts to understand and improve laser induced damage threshold of fused silica optics at the wavelength of
351 nm. For several years, with various industrials and academics partners, we have focused on optimizing the grinding,
lapping and polishing processes to increase materials performance. In this paper, we describe our efforts in various
fields: subsurface damage characterization, lapping process simulation, diamond grinding and lapping machine
instrumentations, ... Our concern is to control and manage the material removal at each step of the process in order to
reduce the cracks region extension and thus to diminish the damage density.
Spatially-engineered "top-hat" laser beams are used in solid-state high-energy lasers in order to increase the energy
extraction efficiency in the amplifiers. To shape the laser beam, an efficient alternative to serrated apertures is to modify
a laser cavity so that it naturally generates this "top-hat" beam, replacing a mirror of the laser cavity by a graded phase
mirror. Its complex shape can be approached by microlithographic techniques based on an iterative mask and etch
technique, but many steps are required to avoid large phase steps. The broad-beam ion-etching technique is well suited to
manufacture such surfaces, with a good precision and a perfectly smooth surface. We shall present the technique we used
for square top-hat beam generation. We shall detail the mask optimisation, combining simultaneous simulation of the ion
etching and the beam build-up in the front-end laser. We shall present the results of the surface testing and the final test
of the component in the laser.
HECOR (HElium CORonagraph) is a coronagraph designed to observe the solar corona at 30.4 nm between 1.2 and 4
solar radii. The instrument is part of the Herschel sounding rocket payload to be flown from White Sands Missile Range
in December 2007. Much like for neutral hydrogen, the residual singly ionized helium present in the corona can be
detected because it resonantly scatters the intense underlying chromospheric radiation. Combined with the simultaneous
measurements of the neutral hydrogen corona made by SCORE, the other coronagraph of the Herschel payload, the
HECOR observations will provide novel diagnostics of the solar wind outflow. HECOR is an externally occulted
coronagraph of very simple design. It uses a triple-disc external occulting system, a single off axis multilayer coated
mirror and a CCD camera. We present measurements of the EUV mirror roughness and reflectivity, tests of the image
quality, and measurements of the stray light rejection performance. The mirror uses a novel multilayer design with three
components that give HECOR a high throughput.
Orbiting around the Sun on an inclined orbit with a 0.2 UA perihelion, the Solar Orbiter probe will provide high resolution views of the Sun from various angles unattainable from Earth. Together with a set of high resolution imagers, the Full Sun Imager is part of the EUV Imaging suite of the Solar Orbiter mission. The mission's ambitious characteristics draw severe constraints on the design of these instruments. We present a photometrically efficient, compact, and lightweight design for the Full Sun Imager. With a 5 degrees field of view, this telescope will be able to see the global solar coronal structure from high viewing angles. Thermal solutions reducing the maximum power trapped in the High Resolution Imagers are also proposed.
Imaging of the solar corona by selecting Fe IX (λ=17.1nm,), Fe XII (λ=19.5nm), Fe XV (λ=28.4nm) and He II (λ=30.4nm) emission lines with a Ritchey-Chretien telescope requires to coat the optics with multilayers having a high accuracy in their layer thicknesses, a high reflectivity and an optimal bandpass. Multilayers were simulated in order to determine the most adequate formula for each wavelength channel. Mo/Si coatings were deposited by using the ion beam sputtering technique in a high vacuum chamber equipped with a micro balance and an in-situ reflectometer. The multilayers were studied by grazing angle reflectometry at 0.1541nm, and their reflectances around the operating wavelengths were measured on the SA62 IAS/LURE beam line of the SuperACO
synchrotron facility located at Orsay. In addition, aging versus time and behavior of the multilayers under a rapid thermal annealing were investigated.
Performances of the ion-beam deposited multilayers have been improved compared to the Mo/Si coatings obtained in the past by the e-beam evaporation technique for the SOHO mission Extreme UV Imaging Telescope (EIT). The EUVI telescopes for the STEREO mission are being proceduced by depositing these new generation of multilayers onto
primary and secondary mirrors. The reflectivity measurements on a telescope are presented.
The MAGRITTE telescopes are part of the SHARPP instrument suite, part of the Solar Dynamics Observatory (SDO), a NASA spacecraft to be launched in a geostationnary orbit in 2007. The MAGRITTE instrument package will provide high resolution images of the solar corona at high temporal frequency simultaneously in 5 EUV and in Ly-α narrow bandpasses. The 1.4 R0 MAGRITTE common field of view complements the other SHARPP instruments, as well as its spectral coverage with 6 narrow bandpasses located within the 19.5 to 120 nm interval. The key challenges of the MAGRITTE instrument are a high angular resolution (0.66 arcsec/pixel) with a high responsivity (exposure times smaller than 8 sec), combined with restricted spacecraft resources. The design of MAGRITTE is based on a high performance off-axis Ritchey-Chretien optical system combined with a large detector (4 K x 4 K, 12 µm pixel). The tight pointing stability performance of 1.2 arcsec over the image exposure time requires an active image motion control, using pointing information of a Guide Telescope, to compensate low frequency boresight variations produced by spacecraft jitter. The thermomechanical design and the mirror polishing are highly critical issues in the instrument design. This paper presents the MAGRITTE design concept with the expected performances based on a realistic error budget. The mirror polishing concept and performances are discussed.
The Solar Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory will characterize the dynamical evolution of the solar plasma from the chromosphere to the corona, and will follow the connection of plasma dynamics with magnetic activity throughout the solar atmosphere. The AIA consists of 7 high-resolution imaging telescopes in the following spectral bandpasses: 1215Å. Ly-a, 304 Å He II, 629 Å OV, 465 Å Ne VII, 195 Å Fe XII (includes Fe XXIV), 284 Å Fe XV, and 335 Å Fe XVI. The telescopes are grouped by instrumental approach: the MAGRITTE Filtergraphs (R. MAGRITTE, famous 20th Century Belgian Surrealistic Artist), five multilayer EUV channels with bandpasses ranging from 195 to 1216 Å, and the SPECTRE Spectroheliograph with one soft-EUV channel at OV 629 Å. They will be simultaneously operated with a 10-second imaging cadence. These two instruments, the electronic boxes and two redundant Guide Telescopes (GT) constitute the AIA suite. They will be mounted and coaligned on a dedicated common optical bench. The GTs will provide pointing jitter information to the whole SHARPP assembly. This paper presents the selected technologies, the different challenges, the trade-offs to be made in phase A, and the model philosophy. From a scientific viewpoint, the unique combination high temporal and spatial resolutions with the simultaneous multi-channel capability will allow MAGRITTE / SPECTRE to explore new domains in the dynamics of the solar atmosphere, in particular the fast small-scale phenomena. We show how the spectral channels of the different instruments were derived to fulfill the AIA scientific objectives, and we outline how this imager array will address key science issues, like the transition region and coronal waves or flare precursors, in coordination with other SDO experiments. We finally describe the real-time solar monitoring products that will be made available for space-weather forecasting applications.
The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI instrument suite currently being developed for the NASA STEREO mission. Identical EUVI telescopes on the two STEREO spacecraft will study the structure and evolution of the solar corona in three dimensions, and specifically focus on the initiation and early evolution of coronal mass ejections (CMEs). The EUVI telescope is being developed at the Lockheed Martin Solar and Astrophysics Lab. The SECCHI investigation is led by the Naval Research Lab. The EUVI’s 2048 x 2048 pixel detectors have a field of view out to 1.7 solar radii, and observe in four spectral channels that span the 0.1 to 20 MK temperature range. In addition to its view from two vantage points, the EUVI will provide a substantial improvement in image resolution and image cadence over its predecessor SOHO-EIT, while complying with the more restricted mass, power, and volume allocations on the STEREO mission.
The LYOT (LYman Orbiting Telescope) solar mission is proposed to be implemented on a micro-satellite of CNES (France) under phase A study. It includes two main instruments, which image the solar disk and the low corona up to 2.5 Ro in the H I Lyman-α line at 121.6 nm. The spatial resolution is about 1” for the disk and 2.5” for corona. It also carries an EIT-type telescope in the He II (30.4 nm) line. The coronagraph needs a super polished mirror at the entrance pupil to minimize the light scattering. Gratings and optical filters are used to select the Lyman-α wavelength. VUV cameras with 2048×2048 pixels record solar images up to every 10 seconds.
The satellite operates at a high telemetry rate (more then 100 kb/s, after onboard data compression). The envisaged orbits are either geostationary or heliosynchronous. Possible launch dates could be end of 2006 - beginning of 2007.
Infrared microspectrometry, using a synchrotron radiation source, has been developed at Super-ACO (LURE-France). In order to accommodate for constrained horizontal (45 mrad) and vertical (18 mrad) collection angles, a particular care has been devoted to the design and making of the extraction optics, in order to achieve the highest brightness as possible, for small area illumination. Experimentally, a net gain of one hundred in Signal to Noise Ratio has been measured for an upper aperture of 3 X 3 micrometers 2. Several applications are currently underway, and some of them, related to Biomedical Science are reported in this paper.
We have used a broad ion beam technique to generate cylindrical structures. Although limited to small dimensions, it produces potentially high precision smooth surfaces. As a first trial, four surfaces were produced for an industrial application, using a fairly simple mask; the 8 mm wide, 3 micrometers deep W profile cylinder was engraved on silicon substrates. Reproducibility was in the range of 1 percent when working in reproducible conditions, allowing refinement of the mask. We shall discuss the limitations of the method and improvement of the mask. We shall discuss a project extending the method to quasi-cylindrical figuring: the fabrication of a diffraction-limited off-axis ellipsoidal mirror at a 21 nm wavelength, with, as a first trial, the fabrication of a toroidal surface to a nanometric precision.
Absolute optical flat testing using the classical three flat method poses repositioning problems and basically only yields one absolute diameter. Although not giving access tot he mean curvature, the method we propose only requires relative displacements and yields a 2D map of the departure of the flat to the best sphere. Simulations and experimental data have been achieved up to a 301 by 301 sampling, showing a repeatability in the neighborhood of 1 nm P-V.
A thin layer of homogeneously oriented nematic liquid crystal (NLC) applied on the optical-quality surface as a free film may visualize, through a polarizing microscope, the images of defects that can not be observed with conventional microscopy: cleaning defects, local physical and chemical surface modifications and microrelief defects. A new vision of polished glass surface defects obtained by the NLC thin-film coating makes it valuable as independent technique for surface quality testing.
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