Grazing Incidence Monochromator Research Articles

A study of molybdenum radiation from alcator A

Radiation emitted by molybdenum impurity ions in the Alcator A tokamak has been investigated. A grazing incidence monochromator photometrically calibrated against synchrotron radiation was used to determine absolute brightnesses of emission lines and the role of molybdenum radiative losses in the plasma discharge power balance. At line average electron densities of 3 × 10 14 cm −3, molybdenum radiation from the central (0–3 cm) region was equal to ∼17% of the local ohmic heating power, implying radiation from molybdenum ions does not dominate the power loss from the central part of the plasma. The temporal behavior of molybdenum ions injected by the laser blow off technique at n e = 3 × 10 14 cm −3 indicated that the molybdenum ion confinement time was finite in conflict with neoclassical theory. At lower densities (1–2 × 10 14 cm −3) the radiation from intrinsic molybdenum increased faster than the electron density during the discharge, indicating a buildup of molybdenum ions in the plasma.

Design and performance of a toroidal grazing incidence monochromator for the 20 – 200 eV photon energy range

A new monochromator using holographically ruled toroidal gratings, has been built for the A61 beam line at the ACO storage ring in Orsay. The performance of the monochromator was evaluated from photoelectron measurements on photoionized rate gases (PAX technique). Measurements of photon flux, efficiency in the various orders, and resolution are summarized.

Design of a high throughput grazing incidence monochromator for surf II

Optimization and ray trace calculations have been completed for a high throughput, toroidal grating monochromator. Several unique features have been incorporated into the design. The instrument will use the electron beam as the entrance slit, taking advantage of the small vertical beam size and high brightness of SURF II. The grating will be placed as close as possible to the storage ring and will intercept 51 mrad of horizontal orbit and below 500 Å, the full vertical light output. Three different gratings will be used to cover the ranges 30–90, 80–200 and 150–600 Å. Normally, multiρating instruments vary only the grating ruling spacing to change ranges, keeping the toroid and monochromator geometries identical in the different ranges. This instrument will be optimized independently in each range using the optimum toroid and monochromator geometries. As a result, the exit arm length will change in going from the long to the middle wavelength range and the included angle will change from 162.2° to 173° in going to the shortest wavelength range.

Optical design of grazing incidence toroidal grating monochromator

Design rules using geometrical optics and physical optics associated with the phase balancing method are discussed for stigmatic toroidal grazing incidence monochromators. To determine the optical performance of devices involving mirrors and/or gratings, ray tracing programs using exact geometry are quite widely used. It is then desirable to have some way to infer the practical performance of an instrument from a spot diagram created by tracing a limited number of rays. We propose a first approach to this problem involving an estimation of the geometrical intensity distribution in the image plane and the corresponding line spread function.

New approaches in analysis of soft X-rays using gratings

The properties of the state-of-the art transmission gratings are discussed and put in context with reflection gratings, zone plates and multi-layer mirrors. Efficiency as well as resolution of the systems are comparable but the different approaches have widely different emphasis and fields of application. The importance of alignment and continuous monitoring of the performance of a grazing incidence monochromator is emphasized and results from an analysis of alignment effects are presented. New developments in multiple combinations of different optical elements are discussed and proposed as important applications of synchrotron radiation.

Mark IV "Grasshopper" grazing incidence monochromator for the Canadian Synchrotron Radiation Facility (CSRF)

The vacuum, mechanical, and optical characteristics of a "Grasshopper" grazing incidence monochromator, for use with a synchrotron radiation source in the 30–300 eV range, is described. The monochromator is compatible with ultrahigh vacuum (≤ 5 × 10−10 Torr throughout), and the motor driven scan mechanism is linear and reliable. The monochromator has been calibrated using several known absorption edges between 36 and 102 eV and a nonlinear least squares fit to the scan equation. These same absorption edges, plus a scan over zero order, show that the present resolution of the monochromator (with 10 and 16 μm exit and entrance slits respectively) is 0.16 Å (0.06 eV at the Al L2.3 edge). With 10 μm entrance and exit slits, the resolution will be very close to the theoretical Δλ = 0.083 Å.

Optimisation of grazing-incidence monochromators

The general characteristics of existing grazing-incidence monochromators are described and the present technological limitations discussed. A total system design approach is emphasized whereby the characteristics of a particular synchrotron light source can be optimally matched to an experimental technique. As an example FLIPPER II, an ultrahigh vacuum grazing-incidence monochromator for photoemission experiments built at the Max-Planck-Institut Stuttgart for use at DESY, Hamburg is briefly described.

The development of toroidal grating monochromators at L.U.R.E.

In the last two years grazing incidence monochromators based on holographic toroidal gratings have been developed at L.U.R.E. The model described in this paper is a 3 m one (entrance slits-grating distance). Due to the large grazing angle (15°) it can be used between 10 and 150 eV ∗. With the Orsay storage ring (A.C.O.) very high flux ( ∼4 × 10 12 phot/ A ̊ · s at 100 eV and good resolution (0.1 Å for 100 μm slits) have been obtained. Due to the large size of the grating (50 × 210 mm 2) no decrease of the intensity has been observed after more than one year of use (>1200 h). Examples of angular resolved photoemission and fluorescence spectra will be shown.

Performances of the lure rowland circle monochromator using gas phase photoelectron spectroscopy up to a photon energy of 280 eV

The performance of the LURE Rowland circle grazing incidence monochromator has been determined up to a photon energy of 280 eV using gas phase photoelectron spectrometry with the PAX method. Suitable converters such as He 1s, Ne 2p, Ar 2p and Ar 3p have been used to study the resolution, the intensity, the contribution of higher orders and the level of stray light. The results obtained with various sorts of gratings (blazed and holographic, 600 lines/mm to 2400 lines/mm, replica and original gratings) are presented. The superiority of the holographic Jobin-Yvon gratings in the high energy region is demonstrated.

EUV Spectrum and Lifetimes of Foil-Excited Phosphorus

Foil excitation of 31P ions at 19 MeV has been used to produce singly and doubly excited states of highly ionized phosphorus atoms. The EUV spectrum in the wavelength range 10 nm < λ < 55 nm has been observed and analyzed by means of a 2.2 m grazing incidence monochromator. General agreement with tabulations based on observations with other light sources has been found. Decay curves of 22 n = 2, Δn = 0 transitions in P IX-P XII have been taken. The evaluation procedure accounts for the spatial resolution function. As in the case of silicon, the decays of singly excited states appear to be strongly fed by cascades from doubly excited states in the n = 2 shell. The lifetime results are in general agreement with theoretical predictions.

Highly resolved EUV beam-foil spectra of silicon

Spectra of foil-excited ions at tandem energies in the EUV region show many unclassified lines. In order to provide a basis for term analysis, high resolution spectra of Si are taken using a ruled 600 l/mm grating in 3rd diffraction order and two holographic gratings of 1,200 l/mm resp. 3,600 l/mm in first diffraction order. With the latter grating the resolution power of a 2.2 m grazing-incidence monochromator is sufficient to measure fine-structure splittings of inter-shell transitions of O VI–O VIII and Si X–Si XII in the wavelength rangeλ < 20 nm. The performance of the gratings is demonstrated.

Radiation due to pseudo-continuum from high-Z impurities in upgraded DIVA tokamak plasma

The many closely crowded lines (pseudo-continuum) of high-Z gold impurities are studied in detail with a calibrated grazing-incidence monochromator in hydrogen plasma, in the upgraded DIVA tokamak device with a divertor; the toroidal field is 20 kG and the peak plasma current is 40 kA. The emission spectrum of the many lines is observed in the wavelength region of 42 to 200 Å. The time-resolved spatial distribution of the emission of the many lines was measured in each element in the wavelength region. It was found that the radiation due to the many lines in the wavelength region of 120 to 200 Å concentrated in an intermediate region of the plasma column, and that the emission of the many lines in the wavelength region of 42–110 Å peaked at the plasma centre. The radiation power loss due to the many lines in the 120–200 Å region was dominant during the whole discharge. The radiation power due to the many lines corresponded to 40–70% of the total radiation power loss from the plasma volume.

Absolute Calibration of a Grazing-Incidence Vacuum Monochromator by Means of Tokamak Discharges

A 3-m grazing-incidence monochromator was calibrated absolutely in the wavelength region from 40 to 1100 Å by means of tokamak discharges. The monochromator was equipped with a platinum-coated ruled grating blazed at 146 Å and a windowless Cu–Be Photomultiplier. Line-pairs used in the atomic-branching-ratio calibration were impurity lines emitted from oxygen and carbon ions, in various ionized states, in JFT-2 and DIVA hydrogen discharges. The effect due to self-absorption was negligibly small for the impurity resonance lines, because the densities of the impurity ions were very low. Errors in the calibration experiment were estimated to be typically within several tens of percent and were largely ascribable to the lack of accuracy in the values of transition probabilities. The absolute sensitivity of the monochromator determined through the present calibration was considered to be sufficiently reliable for the investigation of impurities in high-temperature tokamak plasmas.

Polarization by gratings used at grazing incidence

The polarization introduced by gold-coated and aluminum-coated concave reflection gratings used in a grazing incidence monochromator has been measured over the spectral range from 20 nm to 130 nm. In every case the polarization ratio (P = R(p)/R(s)) is greater than 0.8 for wavelengths less than 40 nm and appears to be approaching unity below 20 nm. For both new and aged or contaminated gratings, the observed polarizations are consistent with those calculated assuming reflection occurs at a plane thin multilayer region with the optical constants chosen to simulate the grating surface.

Thin windowed gas absorption apparatus for use with storage ring synchrotron radiation sources

A thin window gas absorption apparatus suitable for experiments with a storage ring synchrotron radiation source is described. The apparatus has been used with the grazing incidence monochromator on the 4° beam line at the Stanford Synchrotron Radiation Laboratory in experiments studying K-edge absorption in small molecules containing carbon and nitrogen.

A new design for high flux grazing incidence monochromator for synchrotron radiation

Recent experiments at L.U.R.E. (Orsay) have shown the great capacity of grazing incidence monochromators based on holographic toroidal grating, previously described by D. Lepère. Good resolution (1 Å with 100 μm slits) and high flux (>10 11 photons/Å s) have been obtained with a very small model (0.3 m). A more sophisticated version (3 m) of this kind of monochromator has been designed and it is built now at L.U.R.E. (Orsay). The expected performances are described.

Recent instrumentation developments at the university of Wisconsin synchrotron radiation center

Two new monochromators have been installed at the Wisconsin Synchrotron Radiation Center and four more are being designed and constructed for installation later this year. The new instruments installed are an uhv version of a vertically dispersing Seya-Namioka monochromator and an adjustable slit version of the “Grasshopper” grazing incidence monochromator built at the University of Wisconsin Physical Sciences Laboratory for use at the Stanford Synchrotron Radiation Project The new instruments to be installed later are a 4 normal incidence monochromator designed around a high efficiency Bausch and Lomb grating ruled for the Sky Lab Program and three grazing incidence toroidal grating monochromators designed for use with special Jobin-Yvon holographic gratings. The work on the toroidal grating monochromator is proceeding in collaboration with research groups from the IBM Watson Laboratories and the University of Pennsylvania. Operating characteristics achieved or to be expected with these instruments will be discussed.

The SSRL ultrahigh vacuum grazing incidence monochromator: Design considerations and operating experience

Considerable experience has now accumulated with the “grasshopper” monochromator installed on the four degree line at the Stanford Synchrotron Radiation Laboratory. This is one of the first bakeable high vacuum instruments for use with a storage ring source in the photon energy range 25 to 1000 eV. The unique features of this instrument will be discussed from a general point of view, including the source emittance and the transforming properties of the beam line plus monochromator. Actual performance figures will be given in order to better appraise the limits of focusing optics and gratings at two degree grazing incidence. Improvements such as post-monochromator optics, isolation valves and provisions for adjustment will be briefly discussed.

Maximoc, a novel grazing-incidence monochromator for XUV-investigations with synchrotron-radiation

The monochromator described here is a modified Vodar-mount with fixed exit-slit, to be preferentially used in the 5–100 Å range. It has been designed for both transmission and resolution as high as possible and is entirely computer-operated, allowing the automatic scanning of spectra with a ±0.01 A ̊ accuracy.

A grazing incidence monochromator for synchrotron radiation

A grazing incidence monochromator has been constructed using the principle of differential reflectivity for order sorting. Some difficulties associated with earlier designs of this type have been solved and various refinements incorporated. The instrument includes a phase grating of the laminar type, as developed for use in the X-ray region. Details of the design and construction of the monochromator together with measurements of performance are reported, and a comparison with the calculated properties of the grating and optical system is made.