Varied Line Spacing Research Articles

Spectroscopic evaluation of three different gratings used for a flat-field extreme ultraviolet spectrometer to monitor Δn=1 transitions from medium-Z impurities in 10–30Å

Spectral characteristics of varied line spacing 2400 grooves/mm gratings used for a flat-field extreme ultraviolet spectrometer have been evaluated to monitor Delta n=1 (n=2-3) transitions from medium-Z impurities in 10-30 A, where many spectral lines from metallic impurities closely exist. For this purpose emission spectra of the Delta n=1 transitions from partially L-shell-ionized Ti and Fe have been measured in large helical device. At first, a ruled and a holographic grating were utilized for the comparative study. Both gratings suppressed higher order light effectively but spectral sensitivity was much higher for the holographic grating. The ruled grating, however, attained better spectral resolution (0.083 A at 18.97 A) in the 10-100 A range compared to that (0.130 A) of the holographic grating. After that a recently developed new holographic grating with different laminar shapes and line spacings has attempted to improve the spectral resolution. As a result, it has considerably improved the spectral resolution in the 10-30 A range, i.e., approximately 0.090 A. However, it is found that the experimentally obtained spectral resolution is quit poor compared to the computationally simulated one, suggesting a technical difficulty in manufacturing exactly the varied line spacing of the holographic grating at such a short wavelength range.

High resolution soft x-ray spectroscopy of low Z K-shell emission from laser-produced plasmas

A large radius, R=44.3 m, high resolution grating spectrometer (HRGS) with 2400 lines/mm variable line spacing has been designed for laser-produced plasma experiments conducted at the Lawrence Livermore National Laboratory Jupiter Laser Facility. The instrument has been run with a low-noise, charge-coupled device detector to record high signal-to-noise spectra in the 10-50 A wavelength range. The instrument can be run with a 10-20 microm wide slit to achieve the best spectral resolving power, approaching 1000 and similar to crystal spectrometers at 12-20 A, or in slitless operation with a small symmetrical emission source. We describe preliminary spectra emitted from various H-like and He-like low Z ion plasmas heated by 100-500 ps (full width at half maximum), 527 nm wavelength laser pulses. This instrument can be developed as a useful spectroscopy platform relevant to laboratory-based astrophysics as well as high energy density plasma studies.

New model ultra-soft X-ray spectrometer for microanalysis

The authors developed a new general-purpose analytical apparatus that includes a high-resolution ultra-soft X-ray spectrometer, which notably can be used to efficiently measure the ultra-soft X-ray spectrum over the 30–150 eV range. Over this energy range, the analysis of ultra-light elements, such as Li, can be performed, as well as the direct analysis of the chemical bonding state of any element. The motivation for the development of the apparatus was that there is currently no general-purpose apparatus for direct measurement over the ultra-soft X-ray energies of less than 100 eV. The recent developed system is made up of a commercial-base scanning Auger analyzer and the new spectrometer of ultra-soft X-rays. This spectrometer uses two types of flat field spherical varied line spacing gratings, the same focal curve for both grating, a poly-capillary at the input to aid in transmission and to decrease the limitations of the mounting geometry, and a backside-illumination type CCD camera for high sensitivity and high efficiency. This means that the system has no moving parts that can reduce the accuracy of the measurements; an important features. This system was used to measure Li Kα for the first time as a general-purpose apparatus. It was confirmed that the resolution of the measurement exceeded the predefined limits (100; E/ΔE). However, it was difficult to remove higher order interference lines.

Study of a displacement sensor based on transmission varied-line-space phase grating

A displacement sensor based on transmission varied-line-space (VLS) phase gratings is proposed. The relationship between the properties of the sensor and the parameters of VLS is discussed. Compared with the displacement sensor manufactured by the reflective VLS grating, this type of sensor contains a grating with simpler structure and high diffraction efficiency. It also has good stability with the change of temperature.

Commissioning and performance of the variable line spacing plane grating monochromator beamline at the Canadian Light Source

The variable line spacing plane grating monochromator beamline at the Canadian Light Source (CLS) employs three grazing incidence variable line spacing gratings to cover a photon energy range of 5-250 eV. It uses a 185 mm period length planar permanent magnet insertion device as the photon source, sharing a straight section with another soft x-ray beamline at the CLS. The commissioning and performance of the beamline is reported. The high resolution photoabsorption spectra of Ar and PF(5) gases are reported. A resolving power of over 40,000 for photons in the low energy region and >10,000 for a wider energy range (8-200 eV) can be achieved. A photon flux of up to 2 x 10(12) photons/s per 100 mA with slit settings of 50 microm has been measured.

Spectroscopic comparison between 1200grooves∕mm ruled and holographic gratings of a flat-field spectrometer and its absolute sensitivity calibration using bremsstrahlung continuum

A flat-field extreme ultraviolet (EUV) spectrometer with a varied line spacing groove grating (1200 grooves/mm at grating center) has been developed to study the emission spectra from highly ionized medium Z impurities in large helical device (LHD). It covers a wavelength range of 50-500 A using a mechanically ruled grating, which was later replaced by a newly developed laminar-type holographic grating for comparative studies. Differences in spectral resolution, intensities of higher order spectra, and sensitivities of the spectrometer were studied between the two gratings by observing the emission spectra of LHD plasmas. Although the achieved resolution was alike between them, i.e., deltalambda approximately 0.24 A at 200 A, the holographic grating was much superior in suppressing the higher order light than the ruled grating. The relative sensitivity between the two gratings was evaluated using continuum radiation from LHD plasmas. As a result, it was found that the holographic grating has a flat response in the full wavelength range, but the sensitivity of the ruled grating drops sharply below 200 A. A new technique for the absolute calibration of the EUV holographic grating spectrometer was tried by combining the continuum radiation with a branching ratio of C IV lines (3p-3s: 5800 A/3p-2s: 312 A), and an accurate absolute sensitivity has been successfully obtained.

佐賀県立九州シンクロトロン光研究センターにおける軟Ｘ線利用分析ビームライン（ＢＬ１２）

The soft X-ray beamline constructed for an industry application is briefly introduced. The varied line spacing plane grating monochromator (VLS-PGM) has been designed in order to cover the wide-energy range from 40-1000 eV with a set of three focusing mirrors and one grating. The resolving power is expected to be more than 5000 with 10 micron slits. The conventional photoelectron spectrometer is installed with an ion gun, a flood gun and a twinanode X-ray source. The instrument for XAFS measurement is also attached to the main chamber.

SAXES, a high resolution spectrometer for resonant x-ray emission in the 400–1600eV energy range

We present a 5m long spectrometer for soft x rays to be used at a synchrotron radiation beamline for resonant x-ray emission spectroscopy and resonant inelastic x-ray scattering in the 400–1600eV energy range. It is based on a variable line spacing spherical grating (average groove density of 3200mm−1, R=58.55m) and a charge coupled device two dimensional detector. With an x-ray spot on the sample of 10μm, the targeted resolving power is higher than 10 000 at all energies below 1100eV and better than 7000 at 1500eV. The off-line tests made with Al and MgKα1,2 fluorescence emissions indicate that the spectrometer can actually work at 12 000 and 17 000 resolving power at the L3 edges of Cu (930eV) and of Ti (470eV), respectively. SAXES (superadvanced x-ray emission spectrometer) is mounted on a rotating platform allowing to vary the scattering angle from 25° to 130°. The spectrometer will be operational at the ADRESS (advanced resonant spectroscopies) beamline of the Swiss Light Source from 2007.

Varied line spacing plane holographic grating recorded by using uniform line spacing plane gratings

Uniform line spacing plane gratings are introduced into a recording system to generate aspherical wavefronts for recording varied line spacing plane holographic gratings. Analytical expressions of groove parameters are derived to the fourth order. A ray-tracing validation algorithm is provided based on Fermat's principle and a local search method. The recording parameters are optimized to record a varied line spacing plane holographic grating with the aid of derived analytical expressions. A design example demonstrates the exactness of the analytical expressions and the superiority of recording optics with auxiliary gratings.

Development of an Ultra Soft X-ray EPMA Equipped with a Grating Monochrometer and a Poly-capillary

We have developed a newly designed high efficiency spectrometer system for ultra-soft X-rays with a VLS (Varied-Line-Spacing) grating and a two-dimensional CCD detector. This system can be adapted to the analysis of Li with Li Kα at high sensitivity. A polycapillary system is set in the upstream of the instrument as an X-ray lens to condense the ultra-soft X-rays for high efficiency measurement. There are no moving parts such as slit and drive system of grating in this system at all. And, these advantages make it possible to construct the high-resolution ultra-soft X-ray spectrometer with maximum possible desiring transmission efficiency and reproducibility. This instrument can be applied to the precision analysis of the chemical state of Li metallic, which is one of the key elements of the industrial materials such as an electrode material used for a fuel cell or a lithium battery for controlling the process of the reaction with an electrolyte.

High-resolution soft X-ray emission spectrograph at advanced light source

Abstract The progress of valence electronic spectroscopy with X-rays has been largely limited by the challenge of fine instrumentation. Relatively weak scattering cross-section and/or limited (coarse) energy resolution restrict X-ray spectroscopy to address fundamental issues in condensed-matter electron physics. Depending on the nature of excitations, high brightness photon beam from third-generation synchrotron facilities helps raise the count rates to a detectable limit over the noise level. Over the past decade, it has been realized that high-resolution resonant inelastic soft X-ray scattering has the potential to play an important role in understanding complex phenomena observed in highly correlated systems. Driven by such demand, we have developed a soft X-ray emission spectrograph based on variable line spacing (VLS) gratings to work in the soft X-ray and deep UV (the M edge of transition metals) regime. The slit-less design coupled with high quality optical elements and a high quantum efficiency (QE) in-vacuum CCD detector greatly improves the overall throughput. The M edge spectrograph has been demonstrated to have a resolving power better than 10,000 and will be used in conjunction with meV-resolution beamline (MERLIN) at the Advanced Light Source at Lawrence Berkeley National Laboratory.

Beamline for high-resolution angle-resolved photoemission at Saga Light Source

A new beamline for high-resolution angle-resolved photoemission study on solids and surfaces has been constructed at BL13 of Saga Light Source. In order to realize high-resolution in a wide energy range, the monochromator system is composed of the grazing-incidence mount with two varied line spacing plane gratings (VLSPG) and the normal incidence mount with a multilayer-coated plane grating. Relatively, high photon flux and low higher-order light can be obtained using the multilayer-coated plane grating in the boundary region between grazing-incidence and normal-incidence mounts. It is found from ray-tracing simulations that resolving power better than 10,000 and photon flux of 10 10–10 12 photon/s can be obtained. A high-resolution photoemission system with a gated-detector and a mode-locked Ti:Sapphire laser with the regenerative amplifier is installed at the beamline. Using these systems, we can perform the time-resolved high-resolution photoemission study for various photo-excited phenomena and surface dynamics.

Determination of groove spacings for concave diffraction gratings

A long trace profiler (LTP) based method has been reported to measure the groove density of a concave grating with a curvature radius 14346.8 mm. It is appropriate for gratings with a sufficiently large curvature radius. Measurements of the groove density of a concave or convex grating with a small curvature radius could be problematic. A system based on a diffraction method and developed to check the groove variation of variable line spacing (VLS) gratings was used to measure a concave grating at NSRL recently and is the subject of this paper. For a grating with a small radius of curvature, the off-axis errors become dominant factors determining the system uncertainty. The errors are evaluated, and a correction algorithm is developed. A commercially available concave grating with a curvature radius of 750 mm was measured. The maximum relative groove density error (ΔN/N) was 3×10−5.

High resolution, large spectral range, in variable- included- angle soft X-ray monochromators using a plane VLS grating

We give a unified discussion of two different approaches to the design of grazing incidence monochromators with a variable line spacing (VLS) grating for soft X-ray undulator sources. Neither one uses an entrance slit and both work with a fixed position exit slit. In one approach, being constructed at LNLS and designed for the energy range 100 < E < 1000 eV , the choice of the VLS parameters allows for the operation at a variable c-value with a single plane grating and little sacrifice in the maximum resolving power. In this case source size limited resolving power of circa 40 000 is expected at 100 eV. In the second approach, for the storage ring in Wisconsin, two gratings covering the energy range 40 < E < 1500 eV are used, one capable of delivering a resolving power larger than 20 000 at 860 eV and the other lower resolving power but much higher flux.

Flat-field grating spectrometer for high-resolution soft x-ray and extreme ultraviolet measurements on an electron beam ion trap

A R=44.3 m grazing-incidence grating spectrometer has been implemented on the Livermore electron beam ion traps for high-resolution measurements in the soft x-ray and extreme ultraviolet region spanning from below 10 up to 50 Å. The instrument uses a grating with variable line spacing (about 2400 l/mm for a flat field of view. Spectra are recorded with a back-illuminated charge-coupled device detector. The new instrument greatly improves upon the resolution achieved with existing grating spectrometers and complements crystal spectrometers at the shorter wavelengths both in terms of wavelength coverage and polarization independent reflectivity response.

Technique for measuring the groove density of a diffraction grating with elimination of the eccentricity effect

For absolute measurement of groove density of diffraction gratings, we suggest a simple method that utilizes two parallel beams, a rotary beam splitter and single-beam long trace profiler. We use the fact that two parallel beams are focused on a point in the focal plane of a Fourier transform lens. Especially, with elimination of the eccentricity effect, the groove density of a diffraction grating was measured for higher precision than ever before. The eccentricity effect is a shift of the interaction points due to the off-centered rotating mount of grating, which is the essential error source in previous measurements. The method was applied to measure the groove density of a varied line spacing plane grating with a central groove density of 400 line/mm. The groove density error was measured to be 0.01 line/mm rms, with a period measurement error of 0.3 nm rms.

Simulation of mechanically ruled concave diffraction gratings by use of an original geometric theory.

A geometric theory is developed for a spherical concave diffraction grating that has variable line spacing and curved grooves and can be produced with existing technology. The aberration coefficients of this grating are determined. A comparison of these coefficients with the corresponding coefficients of holographic gratings and with CODE V polynomial coefficients gives a clearer understanding of the similarity and difference between mechanically ruled and holographically recorded concave gratings and allows the optimization of these gratings with standard computer programs.

Technique for measuring the groove density of diffraction gratings using the long trace profiler

Diffraction gratings are the most efficient systems for dispersing radiation in the soft x-ray and extreme ultraviolet region. They can have a constant periodic structure or a variable line spacing. The performance of an instrument adopting optics depends on the grating manufacturing errors. These could be both slope errors (routinely measured by various instruments) and undesired groove density variation. The measurement of the groove density is mainly performed with home-made setups, which use the diffraction pattern generated by a laser or, sometimes, the images collected with an atomic force microscope or a scanning tunneling microscope. With the use of a long trace profiler (LTP), an instrument developed to measure the longitudinal profile of a mirror, a method to measure the groove density (and the groove density variation) of a surface diffraction grating was developed. It consists of the measurement of the angle of a particular diffraction order, taking advantage of the extreme angular precision of the LTP. An accuracy of one part per million, or better, in the determination of the groove density constancy/variation, is reached. This method demonstrates the great versatility of the LTP and, in particular, its infinite depth of field.

高分解能プラズマ X 線計測の最前線 6.高分解能分光&amp;bull;画像計測用 X 線光学素子の最前線 6.1 軟 X 線ラミナー型不等間隔溝ホログラフィック回折格子

Laminar-type varied-line-spacing gratings have been widely used for soft x-ray monochromator recently because of the features of low stray lights and higher order lights. We have developed an advanced holographic recording and an ion-beam etching methods for the laminar type varied-line spacing gratings. This report describes a short review of the soft x-ray spectrometers using varied-line-spacing gratings, the fabrication process of the laminar-type holographic gratings, and the performance of the flat field spectrographs equipped with the laminar type varied-line spacing gratings comparing with the mechanically ruled replica gratings. It is concluded that, for the sake of the advanced design and fabrication processes and excellent spectroscopic performance, laminar-type holographic gratings will be widely used for soft x-ray spectrometers for various purposes in the near future.

RECENT DEVELOPMENT IN SOFT X-RAY SPECTROSCOPY OF CORRELATED MATERIALS: HIGH RESOLUTION ABSORPTION AND BULK-SENSITIVE PHOTOEMISSION

An extremely high quality soft X-ray beam line was constructed at BL25SU of SPring-8. A varied line spacing plane grating monochromator (VLSPGM) equipped with gratings with the central groove density of 600 and 1,000/mm can cover the energy region from 0.22 to 2 keV by the use of the fundamental radiation from the twin helical undulator. The energy resolution of VLSPGM is beyond 20,000 at 1 keV. The total resolution of practical photoelectron spectroscopy (PES) of better than 80 meV is achieved at 880 eV. The PES measurements performed above several hundred eV have shown the bulk sensitivity in many materials and provided spectra much different from the surface-sensitive spectra so far obtained below slightly above 100 eV or by He II and I light sources. As a breakthrough, bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) is demonstrated to be a very powerful means of studying the bulk electronic states of correlated electron systems.