In the 2010 horizon, solar space missions such as LYOT and Solar Orbiter will allow high cadence UV observations of the Sun at spatial and spectral resolution never obtained before. To reach these goals, the two missions could take advantage of spectro-imagers. A reflective only optical solution for such an instrument is described in this paper and the first results of the mock-up being built at IAS are shown.
In the frame of EUCLID project, the Calibration Unit of the VIS (VISible Imager) instrument must provide an accurate and well characterized light source for in-flight instrument calibration without noise when it is switched off. The Calibration Unit consists of a set of LEDs emitting at various wavelengths in the visible towards an integrating sphere. The sphere’s output provides a uniform illumination over the entire focal plane. Nine references of LEDs from different manufacturers were selected, screened and qualified under cryogenic conditions. Testing this large quantity of samples led to the implementation of automated testing equipment with complete in-situ monitoring of optoelectronic parameters as well as temperature and vacuum values. All the electrical and optical parameters of the LED have been monitored and recorded at ambient and cryogenic temperatures. These results have been compiled in order to show the total deviation of the LED electrical and electro-optical properties in the whole mission and to select the best suitable LED references for the mission. This qualification has demonstrated the robustness of COTS LEDs to operate at low cryogenic temperatures and in the space environment. Then 6 wavelengths were selected and submitted to an EMC sensitivity test at room and cold temperature by counting the number of photons when LEDs drivers are OFF. Characterizations were conducted in the full frequency spectrum in order to implement solutions at system level to suppress the emission of photons when the LED drivers are OFF. LEDs impedance was also characterized at room temperature and cold temperature.
SPICE is an imaging spectrometer operating at vacuum ultraviolet (VUV) wavelengths, 70.4 – 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the Solar Orbiter mission, which carries 10 science instruments in all, to make observations of the Sun’s atmosphere and heliosphere, at close proximity to the Sun, i.e to 0.28 A.U. at perihelion. SPICE’s role is to make VUV measurements of plasma in the solar atmosphere. SPICE is designed to achieve spectral imaging at spectral resolution >1500, spatial resolution of several arcsec, and two-dimensional FOV of 11 x16arcmins. The many strong constraints on the instrument design imposed by the mission requirements prevent the imaging performance from exceeding those of previous instruments, but by being closer to the sun there is a gain in spatial resolution. The price which is paid is the harsher environment, particularly thermal. This leads to some novel features in the design, which needed to be proven by ground test programs. These include a dichroic solar-transmitting primary mirror to dump the solar heat, a high in-flight temperature (60deg.C) and gradients in the optics box, and a bespoke variable-line-spacing grating to minimise the number of reflective components used. The tests culminate in the systemlevel test of VUV imaging performance and pointing stability. We will describe how our dedicated facility with heritage from previous solar instruments, is used to make these tests, and show the results, firstly on the Engineering Model of the optics unit, and more recently on the Flight Model. For the keywords, select up to 8 key terms for a search on your manuscript's subject.
Euclid-VIS is the large format visible imager for the ESA Euclid space mission in their Cosmic Vision program,
scheduled for launch in 2020. Together with the near infrared imaging within the NISP instrument, it forms the basis of
the weak lensing measurements of Euclid. VIS will image in a single r+i+z band from 550-900 nm over a field of view
of ~0.5 deg2. By combining 4 exposures with a total of 2260 sec, VIS will reach to deeper than mAB=24.5 (10σ) for
sources with extent ~0.3 arcsec. The image sampling is 0.1 arcsec. VIS will provide deep imaging with a tightly
controlled and stable point spread function (PSF) over a wide survey area of 15000 deg2 to measure the cosmic shear
from nearly 1.5 billion galaxies to high levels of accuracy, from which the cosmological parameters will be measured. In
addition, VIS will also provide a legacy dataset with an unprecedented combination of spatial resolution, depth and area
covering most of the extra-Galactic sky. Here we will present the results of the study carried out by the Euclid
Consortium during the period up to the Critical Design Review.
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 Polarimetric and Helioseismic Imager (PHI) on board of Solar Orbiter will observe the Sun to measure the photospheric vector magnetic field and the line-of-sight velocity. It will employ a narrowband filtergraph (FG) to scan the FeI 6173 Å absorption line. At different spectral positions, the polarization state of the incoming light will be analyzed. The FG will provide a tuning range to scan the line, the continuum, and to compensate for the spacecraft radial velocity, as it will approach to the Sun down to 0.28 AU. The FG includes a Fabry-Perot etalon and two narrowband prefilters. The bandpass of the narrowest one has a nominal Full Width at Half Maximum (FWHM) of 2.7 Å. The measurement of the prefilters characteristics is essential for the instrument calibration. Here we present the results of the breadboard prefilters characterization, which is an important milestone in the development of the instrument.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 – 79.0 nm and 97.3 -
104.9 nm. It is a facility instrument on the Solar Orbiter mission. SPICE will address the key science goals of Solar
Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar
atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface
and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive
temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to
10MK. The instrument optics consists of a single-mirror telescope (off-axis paraboloid operating at near-normal
incidence), feeding an imaging spectrometer. The spectrometer is also using just one optical element, a Toroidal Variable
Line Space grating, which images the entrance slit from the telescope focal plane onto a pair of detector arrays, with a
magnification of approximately x5. Each detector consists of a photocathode coated microchannel plate image
intensifier, coupled to active-pixel-sensor (APS). Particular features of the instrument needed due to proximity to the Sun
include: use of dichroic coating on the mirror to transmit and reject the majority of the solar spectrum, particle-deflector
to protect the optics from the solar wind, and use of data compression due to telemetry limitations.
The spectroscopy of the far UV emission lines of the solar spectrum combined with an imaging capability is essential to
understand the physics of the outer solar atmosphere. An imaging Fourier transform spectrometer (IFTSUV) is an
attractive instrumental solution to perform such far-UV solar observations. Working in the far UV involves high
precision metrology to maintain the optical path difference (OPD) during the entire scanning process of the
interferogram. It also involves a compact all-reflection design for UV applications. We present the specification of a
servo-system that enables dynamic tip/tilt alignment compensation and OPD sampling measurement of the IFTSUV
scanning mirror. We also discuss the first experimental results of a breadboard as well as the preliminary design of a
Imaging Fourier Transform Spectrometer working in the far UV (IFTSUV) may be the technical solution to
answer many unsolved problems concerning the physics of the solar outer atmosphere. The VUV domain
highly constrains the instruments design and performances as it demands a high optics surface quality and an
accurate metrology to preserve IFTSUV spectral precision and Signal to Noise Ratio (SNR). We present the
advancements on the specification of a metrology system, meeting the predicted performance requirements of
The study of the outer solar atmosphere requires combining imaging and spectroscopy in the UV lines formed
in the high chromosphere, the transition region and the corona. We start from the science requirements and we
define the instrumental specifications in terms of field-of-view (FOV), spatial, temporal and spectral resolution
and bandpass. We propose two different all-reflection optical architectures based on interferometric techniques:
Spatial Heterodyne Spectroscopy (SHS); and Imaging Transform Spectrometer (IFTS). We describe the different
set-ups and compare the potential performances of the two types of solutions, and discuss their feasibility. We
conclude that IFTS appears to be the best solution, meeting the needs of UV solar physics. However, we point
out the many difficulties to be encountered, especially as far as metrology is concerned.
The study of the Sun in the UV spectral domain is essential for a better understanding of the physical processes
taking place in the solar atmosphere. The main tools for this study are imagers and spectrometers. Nevertheless,
the analysis of imagery data is rapidly limited unless spectral information is available, and the association of
spectrometers and imagers is limited by the lack of coherence between the instruments. Therefore, the design of
an imaging spectrometer in UV is a priority for solar physicists. In the far UV, only all reflective optical systems
can be used thus an imaging Fourier transform spectrometer (IFTS) is the ideal candidate for the realization of
such an instrument. The performances of an IFTS are given by the modulation efficiency. Theoretical study of
performances and scientific objectives lead to technical and operating specifications. A mock-up of an IFTSUV
has been built at IAS to validate the working principle. Its optical design and alignment are described in this
paper. The first results are shown and discussed. Planned modifications of the design are also discussed.
SMESE (SMall Explorer For the study of Solar Eruptions) is a Franco-Chinese microsatellite mission. The scientific
objectives of SMESE are the study of coronal mass ejections and flares. Its payload consists of three instrument
packages : LYOT, DESIR and HEBS. LYOT is composed of a Lyman α (121.6 nm) coronagraph, a Lyman α disk imager and a far UV disk imager. DESIR is an infrared telescope working at 35 μm and 150 μm. HEBS is
a high energy burst spectrometer working in X rays and γ rays covering the 10 keV to 600 MeV range. SMESE
will be launched around 2011, providing a unique opportunity of detecting and understanding eruptions at the
maximum activity phase of the solar cycle in a wide range of energies. The instrumentation on board SMESE is
described in this paper.