J. Culhane, G. Doschek, T. Watanabe, A. Smith, C. Brown, H. Hara, L. Harra, A. James, K. al Janabi, B. Kent, C. Korendyke, J. Lang, J. Mariska, S. Myers, J. Seely, G. Simnett, J. Tandy, R. Thomas, D. Windt
The ISAS/JAXA Solar-B mission includes an Extreme-UV Imaging Spectrometer (EIS). It detects
photons in the wavelength ranges 17 - 21 nm and 25 - 29 nm which include emission lines from several
highly ionised species that exist at temperatures log T = 4.7, 5.6, 5.8, 5.9 and 6.0 - 7.3 K. Instrument
throughput is increased substantially by the use of multilayer coatings optimized for maximum
reflectance in the two selected wavelength bands. The use of back-illuminated CCDs provides
significantly enhanced quantum efficiency over that previously available from microchannel plate
systems. In this paper we will describe the design and operation of the instrument and present its
performance parameters e.g. spectral and spatial resolution and sensitivity. Preliminary results of recent
calibration measurements will be described. The role of EIS in the Solar-B mission will be illustrated
with reference to the anticipated observing strategy for the first three months of the mission which will be
outlined.
This paper describes an instrument concept for imaging spectroscopy of ultraviolet (UV) line emission from the solar corona, in the (30-120) nm wavelength range. The optical design for this Ultraviolet Spectro-Coronagraph (UVSC) instrument concept is an externally occulted, off-axis Gregorian telescope where the secondary mirror is a Toroidal Varied Line-Space (TVLS) grating. A field stop with multiple slits is at the prime focus of the telescope's mirror. This multi-slit field stop is the entrance aperture for the spectrograph. The slits select a number of strips in the field-of-view (FOV) with enough separation to minimize the spectral overlap of the UV lines dispersed by the TVLS grating. The complete two-dimensional imaging of the FOV is obtained by interpolating the slit images along the spectral dispersion direction. This paper discusses the use of an UVSC instrument on HERSCHEL, a NASA sounding-rocket payload. HERSCHEL includes the Sounding-rocket CORonal Experiment (SCORE) that currently comprises a UV Coronagraphic Imager (UVCI) for narrow-band (i.e., λ/Δλ≈10) imaging of the HeII, 30.38 nm, line. Adding a spectroscopic capability (i.e., λ/Δλ ≈ 0.3-1 × 104) to the UVCI would enhance the HERSCHEL's science. This paper presents the ray-tracing results of the expected spectral and spatial performances of a UVSC/SCORE optimised for the HeII, 30.38 nm, line.
The Multi-order Solar EUV Spectrograph (MOSES) is a slitless spectrograph designed to study solar He II emission at 303.8 Å (1 Å = 0.1 nm), to be launched on a sounding rocket payload. One difference between MOSES and other slitless spectrographs is that the images are recorded simultaneously at three spectral orders, m = -1, 0, +1. Another is the addition of a narrow-band multilayer coating on both the grating and the fold flat, which will reject out-of-band lines that normally contaminate the image of a slitless instrument. The primary metrics for the coating were high peak reflectivity and suppression of Fe XV and XVI emission lines at 284 Å and 335 Å, respectively. We chose B4C/Mg2Si for our material combination since it provides excellent peak reflectivity and rejection of out-of-band wavelengths. Measurements of witness flats at NIST indicate the peak reflectivity at 303.8 is 39.0% for a 15 bilayer stack, while suppression ranges from 7.5x to 12.9x at 284 Å and from 3.4x to 15.1x at 335 Å for the individual reflections in the optical path. We present the results of coating the MOSES flight gratings and fold flat, including the spectral response of the fold flat and grating as measured at NIST's SURF III and Brookhaven's X24C beamline, respectively.
This paper describes an instrument for imaging spectroscopy of ultraviolet (UV) line emission from the solar corona, in the 0.3-1.2x102 nm wavelength range. The optical design for this Ultraviolet Spectro-Coronagraph (UVSC) is an externally occulted, off-axis Gregorian telescope where the secondary mirror is a Toroidal Varied Line-Space (TVLS) grating. A field stop with multiple slits is at the prime focus of the telescope’s mirror. This multi-slit field stop is the entrance aperture for the spectrograph. The slits select a number of strips in the field-of-view (FOV) with enough separation to minimize the spectral overlap of the UV lines dispersed by the TVLS grating. This type of gratings allows for a much larger stigmatic FOV (i.e., 3° x 4°) in both the spatial and spectral direction than that of the Toroidal Uniform Line-Space (TULS) gratings. The complete imaging of the FOV is obtained by interpolating the slit images along the spectral dispersion direction. As an example, this paper discusses the possible use of a UVSC instrument on HERSCHEL, a NASA sounding-rocket payload, and on Solar Orbiter (SOLO), an ESA mission. HERSCHEL includes the Sounding CORona Experiment (SCORE) that comprises a UV Coronagraphic Imager (UVCI) for narrow-band (i.e., λ/Δλ≈10) imaging of the HeII, 30.4 nm, line. How a spectroscopic capability (i.e., λ/▵λ ≈0.3-1 x 104) would enhance the HERSCHEL science is discussed. The SOLO mission is planned for launch in 2013. Its orbital profile will bring the spacecraft as close to the Sun as 0.22 A.U. Also SOLO would represent an ideal and unique platform for a compact UVSC instrument (i.e., ≈ 1-m length) capable of obtaining simultaneous imaging and spectroscopy of the UV corona. The expected optical performances are presented for a UVSC/SOLO optimised for the OVI doublet, 103.2/103.7 nm.
Imaging spectroscopy at wavelengths below 2000 Å offers an especially powerful method for studying many extended high-temperature astronomical objects, like the Sun and its outer layers. But the technology to make such measurements is also especially challenging, because of the poor reflectance of all standard materials at these wavelengths, and because the observation must be made from above the absorbing effects of the Earth's atmosphere. To solve these problems, single-reflection stigmatic spectrographs for XUV wavelengths have bee flown on several space missions based on designs with toroidal uniform line-space (TULS) or spherical varied line-space (SVLS) gratings that operate at near normal-incidence. More recently, three solar EUV/UV instruments have been selected that use toroidal varied line-space (TVLS) gratings; these are SUMI and RAISE, both sounding rocket payloads, and NEXUS, a SMEX satellite-mission. The next logical extension to such designs is the use of elliptical surfaces for varied line-space (EVLS) rulings. In fact, EVLS designs are found to provide superior imaging even at very large spectrograph magnifications and beam-speeds, permitting extremely high-quality performance in remarkably compact instrument packages. In some cases, such designs may be optimized even further by using a hyperbolic surface for the feeding telescope. The optical characteristics of two solar EUV spectrometers based on these concepts are described: EUS and EUI, both being developed as possible instruments for ESA's Solar Orbiter mission by consortia led by RAL and by MSSL, respectively.
We present the optical design of the spectrometer for imaging spectroscopy in the extreme-ultraviolet (EUV) spectral region for the Solar Orbiter mission. The instrument consists of a telescope making an image of the Sun on an entrance slit of a grating spectrometer. Two different optical designs are presented: a) a normal-incidence off-axis paraboloid telescope feeding a normal-incidence spectrometer and b) a grazing-incidence Wolter-type telescope feeding a normal-incidence spectrometer. The spectral region of operation is the 58-63 nm region, with the possibility of extending the range to the 116-126 nm region. The two designs are discussed in terms of optical performance, effective area and thermal load.
This paper will describe the objectives of the Marshall Space Flight Center (MSFC) Solar Ultraviolet Magnetograph Investigation (SUMI) and the optical components that have been developed to meet those objectives. In order to test the scientific feasibility of measuring magnetic fields in the UV, a sounding rocket payload is being developed. This paper will discuss: (1) the scientific measurements that will be made by the SUMI sounding rocket program, (2) how the optics have been optimized for simultaneous measurements of two magnetic lines CIV (1550Å) and MgII (2800Å), and (3) the optical, reflectance, transmission and polarization measurements that have been made on the SUMI telescope mirrors and polarimeter.
It is a particular challenge to develop a stigmatic spectrograph for EUV wavelengths since the very low normal-incidence reflectance of standard materials most often requires that the design be restricted to a single optical element which must simultaneously provide both re-imaging and spectral dispersion. This problem has been solved in the past by the use of toroidal gratings with uniform line-space rulings (TULS). A number of solar EUV spectrographs have been based on such designs, including SOHO/CDS, Solar-B/EIS, and the sounding rockets SERTS and EUNIS. More recently, Kita, Harada, and collaborators have developed the theory of spherical gratings with varied line-space rulings (SVLS) operated at unity magnification, which have been flown on several astronomical satellite missions. These ideas are now combined into a spectrograph concept that considers varied-line space grooves ruled onto toroidal gratings. Such TVLS designs are found to provide excellent imaging even at very large spectrograph magnifications and beam-speeds, permitting extremely high-quality performance in remarkably compact instrument packages. Optical characteristics of two solar spectrographs based on this concept are described: SUMI, proposed as a sounding rocket experiment, and NEXUS, proposed for the Solar Dynamics Observatory mission.
The dynamic solar atmosphere poses a severe observational challenge for imaging spectroscopy in EUV. The traditional method of building up images by rastering a slit spectrograph has so far proven too slow to keep up with the Sun's rapidly changing transition region and corona. We describe a new approach, using a slitless imaging spectrograph operating in a narrow band, with imaging detectors at three orders. This arrangement offers cotemporal imaging and spectroscopy at high spatial, spectral, and temporal resolution. The prospect of disentangling spatial and spectral information is greatly improved by choosing a narrow band containing only two spectral lines, and by imaging at several spectral orders. This paper discusses several advantages and challenges of the multi-order slitless approach. We derive a mathematical description of the null space of spatial-spectral signatures to which an ideal three-order slitless spectrograph has zero response. An exploration of the null space helps to clarify the capabilities and limitations of this instrument type. We infer that the three-order slitless spectrograph is sensitive to line intensity, doppler shift and line width; but insensitive to line asymmetry. Strategies are developed to minimize the ambiguity in interpreting the multi-order data. A proof of concept sounding rocket payload, the Multi-Order Solar EUV Spectrograph (MOSES), is under development with an anticipated launch in Spring, 2004.
GSFC is in the process of assembling a solar EUV Normal-Incidence Spectrometer called EUNIS, to be flown as a sounding rocket payload. This instrument builds on the many technical innovations pioneered by our highly successful SERTS experiment over its past ten flights. The new design has improved spatial and spectral resolutions, as well as 100 times greater sensitivity, permitting EUV spectroscopy with a temporal resolution near 1 second for the first time ever. To achieve such high time cadence, a novel Active-Pixel-Sensor detector is being developed as a key component of our design. The high sensitivity of EUNIS allows entirely new studies of transient coronal phenomena, such as the rapid loop dynamics seen by TRACE, and searches for non-thermal motions indicative of magnetic reconnection or wave heating. The increased sensitivity also permits useful EUV spectra at heights of 2-3 solar radii above the limb, where the transition between the static corona and the solar wind might occur. In addition, the new design features two independent optical systems, more than doubling the spectral bandwidth covered on each flight. Its 300-370A bandpass includes He II 304A and strong lines from Fe XI-XVI, extending the current SERTS range of 300-355A to further improve our ongoing series of calibration under-flights for SOHO/CDS and EIT. The second bandpass of 170-205A has a sequence of very strong Fe IX-XIII lines, and allows under-flight support for two more channels on SOHO/EIT, two channels on TRACE, one on Solar-B/EIS, and all four channels on the STEREO/EUVI instrument. First flight of the new EUNIS payload is presently scheduled for 2002 October.
Traditional magnetographs measure the solar magnetic field at the visible 'surface' of the Sun, the photosphere. The Solar Ultraviolet Magnetograph Investigation (SUMI) is a hardware development study for an instrument to measure the solar magnetic field higher in the atmosphere, in the upper chromosphere and in the transition region at the base of the corona. The magnetic pressure at these levels is much stronger than the gas pressure (in contrast to the situation at the photosphere), so the field controls the structure and dynamics of the atmosphere. Rapid changes in the magnetic structure of the atmosphere become possible at this height, with the release of energy. Measurements of the vector magnetic field in this region will significantly improve our understanding of the physical processes heating the Sun's upper atmosphere and driving transient phenomena such as flares and coronal mass ejections. The instrument will incorporate new technologies to achieve the polarization efficiencies required to measure the magnetic splitting of lines in the VUV an UV (CIV at 1550 angstrom and MgII at 2800 angstrom). We describe the scientific goals, the optical components that are being developed for a sounding rocket program, and the SUMI baseline design.
Alexander Ignatiev, Nikolai Kolachevsky, Viatcheslav Korneev, Viktor Krutov, Sergey Kuzin, Alexander Mitrofanov, Andrey Pertzov, Eugene Ragozin, Vladimir Slemzin, Igor Tindo, Igor Zhitnik, Nikolai Salashchenko, Roger Thomas
The paper describes the main characteristics of the X-ray optical elements (multilayer spherical and aspherical mirrors and diffraction gratings for the 13-30 nm XUV spectral region, Bragg crystal spherical mirrors for the 0.18 and 0.84 m soft X-ray spectral regions) manufactured for the TEREK-C solar XUV telescope array and the RES-C solar spectroheliograph. The TEREK-C and RES-C instruments were placed aboard the CORONAS-I satellite which was launched on March 2, 1994. The testing procedures and results of laboratory tests in X-ray spectral range are also presented.
Spartan Lite is a proposed series of very low-cost spacecraft missions which offer potential flight opportunities for pointed solar experiments. Early versions will be launched as Space Shuttle attached payloads with the capability of being released for free flight. They would not be recovered, allowing useful lifetimes of six months to one year. An expendable launch vehicle option will be added later. The spacecraft is 3-axis stabilized with a cylindrical instrument cavity 100 cm long and 36 cm in diameter. If approved, the program would provide multiple launch opportunities during the upcoming solar maximum. A conceptual instrument design for a solar pointed mission on Spartan Lite is shown and discussed. The Extreme-Ultraviolet Normal Incidence Spectrograph will observe the solar spectrum between 290 and 466 A with high spatial and spectral resolutions. The large bandpass is due to the compact design, fitting two optical systems into the instrument cavity, each observing a different, but overlapping, wavelength range.
The coronal diagnostic spectrometer is designed to probe the solar atmosphere through the detection of spectral emission lines in the extreme ultraviolet wavelength range 15.0 - 80.0 nm. By observing the intensities of selected lines and line profiles, it is possible to derive temperature, density, flow, and abundance information for the plasmas in the solar atmosphere. Spatial resolution down to a few arcseconds and temporal resolution of seconds, allows such studies to be made within the fine-scale structure of the solar corona. Furthermore, coverage of a large wavelength band provides the capability for simultaneously observing the properties of plasma across the wide temperature ranges of the solar atmosphere. The CDS design makes use of a Wolter-Schwarzschild II telescope which simultaneously illuminates two spectrometer systems, one operating in normal incidence the other in grazing incidence. In this paper we describe the salient features of the design of the CDS instrument and discuss the performance characteristics of CDS as established through pre-delivery test and calibration activities.
The instrument SUMER (solar ultraviolet measurements of emitted radiation) is designed to investigate structures and associated dynamical processes occurring in the solar atmosphere from the chromosphere through the transition region to the inner corona, over a temperature range from 104 to 2 multiplied by 106 K and above. The observations will be performed, on board SOHO (solar and heliospheric observatory) scheduled for launch in November 1995, by a scanning, normal-incidence telescope/spectrometer system in the wavelength range from 500 to 1610 angstrom. Spatial resolution requirements compatible with the pointing stability of SOHO are less than 1000 km corresponding to about 1-arcsec angular resolution. Doppler observations of EUV line shifts and broadenings should permit solar plasma velocity measurements down to 1 km s-1. We report here on some specific features of this instrument related to its pointing as well as its spatial and spectral resolution capabilities.
Verification of component specification and EUV optical performance for the diffraction gratings of the normal incidence EUV spectrograph of SOHO/CDS is discussed. This discussion includes: a comparison of experimentally obtained EUV spectral images of a point source with corresponding ray trace analysis, in-band Lyman alpha leak determination, verification of toroidal radii of curvature, verification of blaze direction by calculation and VUV measurement, and zero order efficiency at 124 nm.
A multilayer coated high density toroidal grating was flown on a sounding rocket experiment in the Solar EUV Rocket Telescope and Spectrograph (SERTS) instrument. To our knowledge this is the first space flight of a multilayer coated grating. Pre-flight performance evaluation showed that the application of a 10-layer Ir/Si multilayer coating to the 3600 l/mm blazed toroidal replica grating produced a factor of 9 enhancement in peak efficiency near the design wavelength around 30 nm in first order over the standard gold coating, with a measured EUV efficiency that peaked at 3.3 percent. In addition, the grating''s spectral resolution of better than 5000 was maintained. The region of enhanced grating efficiency due to the multilayer coating is clearly evident in the flight data. Within the bandpass of the multilayer coating, the recorded film densities were roughly equivalent to those obtained with a factor of six longer exposure on the previous flight of the SERTS instrument.
Performance of a multilayer coated diffraction grating has been evaluated in the
EUV. The application of a multilayer coating to a blazed toroidal grating of high
ruling density has produced a significant enhancement in grating efficiency in the
30 run spectral region in first order and has maintained the excellent quasi
stigmatic spectral resolution of the grating.
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