Soft X-ray Spectrograph Research Articles

Design and experimental evaluation of enhanced diffraction efficiency of lanthanum-based material coated laminar-type gratings in the boron K-emission region.

Numerical and experimental studies have been performed to evaluate the enhancement of diffraction efficiency of diffraction gratings around B $K$-emission by overcoating lanthanum series layers on conventional metal-coated laminar-type gratings. We propose an optical design method based on the concept of spectral flux given by collection efficiency and diffraction efficiency. A diffraction grating with a small angle of incidence provides an advantage to soft x-ray spectrographs because it collects the emission at a larger solid angle compared to that of conventional grazing incidence diffraction gratings. Numerical calculations indicated that La and ${\rm{La}}{{\rm{F}}_3}$ were promising as overcoating materials on a laminar-type Ni-coated diffraction grating, and we performed an experimental study using ${\rm{La}}{{\rm{F}}_3}$ and La/C overcoatings, considering their producibility and durability. The diffraction efficiencies were measured using a reflectometer at a synchrotron facility. The diffraction efficiencies observed at 183.4 eV were 29.4% and 34.3% at angles of incidence of 85.1° and 84.9° for ${\rm{Ni}}/{\rm{La}}{{\rm{F}}_3}$ and Ni/La/C gratings, respectively.

Large-format X-Ray Reflection Grating Operated in an Echelle-like Mounting

Abstract We report on resolving power measurements of an X-ray reflection grating designed for use in an astronomical soft X-ray spectrograph. The grating was patterned via electron-beam lithography (EBL) to have fanned grooves to match the convergence of an illuminating beam. Grating measurements were conducted in an echelle-like mounting, which yields access to high diffraction orders in the soft X-ray bandpass (0.2–2.0 keV). By comparing the zeroth-order line-spread function to the telescope focus, we find evidence for minimal broadening (<1″) introduced by the figure of the grating. In addition, we fit for the spectral resolution (R = λ/Δλ) intrinsic to this grating using a Bayesian Markov Chain Monte Carlo approach. Using an ensemble fitting technique, we find that the grating resolution R exceeds 2200 (3σ lower bound). This current grating resolution meets the performance required for a notional soft X-ray grating spectroscopy mission measuring hot baryonic material in the extended halos of galaxies. Using ray-trace simulations, we identify a geometric aberration resulting from path length differences across the width of the grating as a limiting factor in assessing the resolution of these gratings and discuss methods for placing better constraints on the inherent resolution of X-ray astronomical reflection gratings fabricated using EBL.

High-efficiency in situ resonant inelastic x-ray scattering (iRIXS) endstation at the Advanced Light Source.

An endstation with two high-efficiency soft x-ray spectrographs was developed at Beamline 8.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory. The endstation is capable of performing soft x-ray absorption spectroscopy, emission spectroscopy, and, in particular, resonant inelastic soft x-ray scattering (RIXS). Two slit-less variable line-spacing grating spectrographs are installed at different detection geometries. The endstation covers the photon energy range from 80 to 1500 eV. For studying transition-metal oxides, the large detection energy window allows a simultaneous collection of x-ray emission spectra with energies ranging from the O K-edge to the Ni L-edge without moving any mechanical components. The record-high efficiency enables the recording of comprehensive two-dimensional RIXS maps with good statistics within a short acquisition time. By virtue of the large energy window and high throughput of the spectrographs, partial fluorescence yield and inverse partial fluorescence yield signals could be obtained for all transition metal L-edges including Mn. Moreover, the different geometries of these two spectrographs (parallel and perpendicular to the horizontal polarization of the beamline) provide contrasts in RIXS features with two different momentum transfers.

Effect of curve groove on the spectral resolution for soft X-ray holographic flat-field gratings

The soft X-ray spectrograph is an important instrument for plasma diagnostics. As the core optical element of spectrograph, holographic flat-field grating is fabricated by aspheric wave-front recording optics, so grooves on the surface are curve. The curve grooves of the grating would affect the spectral image properties, thus influencing spectral resolutions. In the design of recording optics, only the groove density distribution on the surface in meridian line should be guaranteed, so optimized recording optics is not unique. Thus gratings with different curvatures of grooves but with expected groove density distribution could be obtained. For holographic flat-field gratings used in a 0.8-6 nm region, we analyze the influences of different curve grooves on the spectral image by ray tracing, and find that the almost straight grooves which are obtained by means of cylinder mirror can obtain the better spectral images. The theoretical results show that the spectral resolutions of grating with almost straight grooves are obviously improved compared with curve grooves, the theoretical spectral resolutions increase from 626 to 953 at 3 nm and from 635 to 1222 at 5 nm, respectively.

Optically Aligned, Space Resolving, Extreme Ultra-Violet and Soft X-ray Spectrograph

We describe in this paper an extreme ultra-violet/soft X-ray (XUV) spectrograph with high sensitivity, high spectral resolution and spatial resolution, which we developed to record XUV emission from a 10 J laser-irradiated gas jet. This spectrograph uses a flat field grazing incidence grating and a grazing incidence collection and imaging mirror. We designed a system where initial positions of elements can be set with a low accuracy of half a millimeter and where the final alignment is done with a visible light low intensity laser beam. High spectral resolution, good spatial resolution and nominal dispersion function have been achieved. A few illustrative results are presented.

Laminar and blazed type holographic gratings for a versatile soft x-ray spectrograph attached to an electron microscope and their evaluation in the 50–200 eV range

Laminar and blazed type holographic varied-line-spacing spherical gratings for use in a versatile soft x-ray flat-field spectrograph attached to an electron microscope are designed, fabricated, and evaluated. The absolute diffraction efficiencies of laminar (or blazed) master and replica gratings at 86.00° incidence evaluated by synchrotron radiation show over 5% (or 8%) in the 50-200 eV range with the maxima of 22% (or 26%-27%). Also the resolving power evaluated by a laser produced plasma source is in excess of 700 at the energy near the K emission spectrum of lithium (~55 eV) for all gratings. Moreover, the K emission spectrum of metallic Li with high spectral resolution is successfully observed with the spectrograph attached to a transmission electron microscope.

RE-INTERPRETATION OF SUPRA-ARCADE DOWNFLOWS IN SOLAR FLARES

Following the eruption of a filament from a flaring active region, sunward-flowing voids are often seen above developing post-eruption arcades. First discovered using the soft X-ray telescope aboard Yohkoh, these supra-arcade downflows (SADs) are now an expected observation of extreme ultra-violet (EUV) and soft X-ray coronal imagers and spectrographs (e.g, TRACE, SOHO/SUMER, Hinode/XRT, SDO/AIA). Observations made prior to the operation of AIA suggested that these plasma voids (which are seen in contrast to bright, high-temperature plasma associated with current sheets) are the cross-sections of evacuated flux tubes retracting from reconnection sites high in the corona. The high temperature imaging afforded by AIA's 131, 94, and 193 Angstrom channels coupled with the fast temporal cadence allows for unprecedented scrutiny of the voids. For a flare occurring on 2011 October 22, we provide evidence suggesting that SADs, instead of being the cross-sections of relatively large, evacuated flux tubes, are actually wakes (i.e., trailing regions of low density) created by the retraction of much thinner tubes. This re-interpretation is a significant shift in the fundamental understanding of SADs, as the features once thought to be identifiable as the shrinking loops themselves now appear to be "side effects" of the passage of the loops through the supra-arcade plasma. In light of the fact that previous measurements have attributed to the shrinking loops characteristics that may instead belong to their wakes, we discuss the implications of this new interpretation on previous parameter estimations, and on reconnection theory.

基于光子筛的软X光谱仪

基于光子筛的软X光谱仪

A compact soft X-ray spectrograph combining high efficiency and resolution

A compact and light weight soft X-ray spectrograph covering 5−35 nm and employing a toroidal mirror and a variable line space reflection grating has been newly developed. Particular emphasis has been placed on achieving a large collection solid angle (1.9 × 10−3 sr) and a high efficiency of the components in order to enable Thomson Scattering plasma diagnostics which has a small total cross section (6.65 × 10−25 cm2). The instrument achieves a signal-to-noise ratio of 5 with a 13.5 nm source which isotropically emits 2.5 × 105 photons. A resolution λ/Δλ = 330 was measured at 21 nm and the dispersion was calibrated. The instrument is housed inside a DN 100 CF ultra high vacuum manipulator (43 × 46 × 47 cm3) which allows positioning relative to the source within ±5 mm and ±50 mm in X,Y and Z direction, respectively. It can be used with or without entrance pinhole and is equipped with a motorized grating, a filter wheel with five filters, and a shutter. Altogether, these features make the spectrograph a versatile instrument which can be employed in a variety of physics applications such as line and bremsstrahlung spectroscopy or Thomson scattering.

Development of soft X-ray multilayer laminar-type plane gratings and varied-line-spacing spherical grating for flat-field spectrograph in the 1–8 keV region

W/C and Co/SiO 2 multilayer laminar-type holographic plane gratings (groove density 1/σ = 1200 lines/mm) in the 1–8 keV region are developed. For the Co/SiO 2 grating the diffraction efficiencies of 0.41 and 0.47 at 4 and 6 keV, respectively, and for the W/C grating 0.38 at 8 keV are observed. Taking advantage of the outstanding high diffraction efficiencies into practical soft X-ray spectrographs a Mo/SiO 2 multilayer varied-line-spacing (VLS) laminar-type spherical grating (1/σ = 2400 lines/mm) is also developed for use with a flat field spectrograph in the region of 1.7 keV. For the Mo/SiO 2 multilayer grating the diffraction efficiencies of 0.05–0.20 at 0.9–1.8 keV are observed. The FWHMs of the measured line profiles of Hf-Mα 1(1644.6 eV), Si-Kα 1(1740.0 eV), and W-Mα 1 (1775.4 eV) are 13.7 eV, 8.0 eV, and 8.7 eV, respectively.

Plasma Spectroscopy in the Tandem Mirror GAMMA 10

Impurity ion radiation intensity has been studied in the GAMMA 10 plasma using both a collisional-radiative model (CR-model) and spectroscopic measurements. We have constructed absolutely calibrated soft X-ray, vacuum ultraviolet, ultraviolet and visible spectrographs for plasma diagnostics. Steady state CR-model calculation for carbon ions is used to obtain the carbon ion emissivities in the plasma. The CR-model calculation results of carbon ion radiation intensities are comparable to the results obtained by the impurity ion spectroscopy. Moreover, plasma rotation measurements are carried out in order to obtain radial electric potential profiles.

SPACE-RESOLVING VUV AND SOFT X-RAY SPECTROSCOPY IN THE TANDEM MIRROR GAMMA 10 PLASMA

Vacuum ultraviolet (VUV) and soft X-ray (SX) spectroscopic measurements are important means to diagnose radiation power loss, impurity ion densities and effective charge of confined plasma, Z eff , in magnetically confined plasmas such as fusion plasmas. We have constructed space- and time-resolving flat-field VUV (150–1050Å) and SX (20–350Å) spectrographs by using aberration-corrected concave gratings with varied line spacing. Absolute calibration experiments have been conducted at the Photon Factory in the High Energy Accelerator Research Organization. Absolute sensitivities of the VUV and SX spectrographs have been obtained for the two (S and P) polarization geometries. Thus, absolute intensities of emission spectra from impurity ions can be measured together with their radial distributions in plasmas. The total radiation power was determined to be less than 6 kW within ±20% of error in our normal plasma operation. Density profiles of impurity ions were reduced by using absolute emissivities of impurity lines and a collisional-radiative model. Moreover, the value of Z eff is estimated to be 1.00 in the tandem mirror GAMMA 10 plasma.

Absolute calibration of space-resolving soft X-ray spectrograph for plasma diagnostics

A grazing incidence flat-field soft X-ray (20–350 Å) spectrograph was constructed and applied for impurity diagnostics in the GAMMA 10 fusion plasma. The spectrograph consisted of a limited height entrance slit, an aberration-corrected concave grating, a microchannel-plate intensified detector and an instant camera/a high speed solid state camera. An absolute calibration experiment for the SX spectrograph was performed at the Photon Factory in the High Energy Accelerator Research Organization with monitoring the incident synchrotron beam intensity by using an absolutely calibrated XUV silicon photodiode. From the results of absolute calibration of the spectrograph, the radiation loss from the plasma was obtained.

In situ calibration of a flat-field grazing incidence spectrograph with an x-ray charge-coupled device camera using a transmission grating and a laser-produced plasma for x-ray laser research

An in situ calibration experiment of a soft x-ray spectrograph for x-ray laser research has been performed. The calibrated spectrograph was a flat-field grazing incidence spectrometer with an x-ray charge-coupled device camera. The absolute sensitivity of the spectrograph was obtained for the wavelength range from 2.6 to 4.0 nm using a transmission grating spectrograph as a reference spectrograph set along the axial direction of a line-focused laser-produced plasma. The absolute sensitivity determined in this work shows nearly the same value as that deduced from the calibration experiment using synchrotron radiation.

Calibration of space-resolving VUV and soft X-ray spectrographs for plasma diagnostics.

Vacuum ultraviolet (VUV) and soft X-ray measurements are important means of diagnosing impurities in magnetically confined plasmas used in fusion research. Recently, space- and time-resolving flat-field VUV (150-1050 A) and soft X-ray (20-350 A) spectrographs have been constructed by using aberration-corrected concave gratings with varied-spacing grooves which give a wide simultaneous spectral coverage on a microchannel-plate intensified detector. Calibration experiments have been performed at beamlines 11A and 11C at the Photon Factory of the High Energy Accelerator Research Organization. The relative efficiency of the VUV spectrograph has been measured for P-polarization geometry in the spectrograph. In the soft X-ray spectrograph, efficiencies have been obtained for several different points of irradiation on the grating along the groove direction and for two (S and P) polarization geometries.

Absolute calibration of a soft X-ray spectrograph for X-ray laser research using white beam.

Absolute calibration of a soft X-ray spectrograph has been performed using a white beam of synchrotron radiation. The calibrated spectrograph was a flat-field grazing-incidence spectrograph with an X-ray CCD detector for X-ray laser research. Absolute sensitivity of the spectrograph system can be obtained from transmitted spectra using filters made of several different materials, each providing an absorption-edge wavelength standard. The absolute sensitivity determined in this work shows nearly the same behaviour with wavelength as that in another calibration experiment using a laser-produced plasma as an X-ray source.

Calibration of charge coupled devices and a pinhole transmission grating to be used as elements of a soft x-ray spectrograph

The development of new types of sophisticated soft x-ray sources requires the knowledge of their emission characteristics such as photon flux, spectral distribution, and size of the radiation source. Calibrated spectrographs for the soft x-ray region are needed to determine these properties. The components of a soft x-ray spectrograph consisting of a pinhole gold transmission grating and a charge coupled device (CCD) camera are calibrated at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt using the synchrotron radiation facility BESSY. Two different kinds of CCD-based photon detectors (one thinned and back illuminated, one coated with a phosphorous layer) are compared with regard to their sensitivities in the spectral range between 50 eV and 1.7 keV. The results obtained for the thinned CCD are compared with theoretical calculations of the sensitivity.

Soft X-ray Emission Spectroscopy at ESRF Beamline 26 Based on a Helical Undulator

A new soft X-ray spectrograph for X-ray emission spectroscopy excited by synchrotron radiation is presented. The apparatus is now installed on beamline 26 at the ESRF in Grenoble. A brief description of the beamline is given and then several components of the spectrograph are covered in more detail. Results of experiments performed both with direct non-monochromated undulator radiation and with monochromated radiation are reported.

Comparison of solar flare emission measures from broadband soft X-ray and ultraviolet spectrograph observations

Joint observations of a solar flare were obtained by the AS&E Imaging X-ray Telescope and the NRL High Resolution Telescope and Spectrograph (HRTS). We compare emission measures from soft X-ray and HRTS data. A small isolated X-ray loop close to the HRTS slit position has an emission measure n e 2ΔL of 3.5×10 29 cm −5, compared to an emission measure of 2.7×10 29 cm −5 obtained from the intensity of flaring Fe XXI 1354 Å plasma along the HRTS slit.

A simple method for overcoming spatial resolution limitations in soft x-ray spectrograph/detector systems

We describe a simple method for improving the spectral resolution of soft x-ray and extreme ultraviolet spectrographs which use electro-optical detector/intensifiers. In this method, the spectrometer is focused onto a narrow slit which is angled near 90° with respect to the dispersive axis and placed just in front of the detector. Proper choice of the width and angle of the slit is shown to have the effect of expanding the spectrum along the length of the slit to the point where the spatial resolution limitations of the detector are overcome.