Two extended x-ray absorption fine structure flat crystal x-ray spectrometers (EFX's) were designed and built for high-resolution x-ray spectroscopy over a large energy range with flexible, on-shot energy dispersion calibration capabilities. The EFX uses a flat silicon [111] crystal in the reflection geometry as the energy dispersive optic covering the energy range of 6.3-11.4 keV and achieving a spectral resolution of 4.5 eV with a source size of 50 μm at 7.2 keV. A shot-to-shot configurable calibration filter pack and Bayesian inference routine were used to constrain the energy dispersion relation to within ±3 eV. The EFX was primarily designed for x-ray absorption fine structure (XAFS) spectroscopy and provides significant improvement to the Laboratory for Laser Energetics' OMEGA-60 XAFS experimental platform. The EFX is capable of performing extended XAFS measurements of multiple absorption edges simultaneously on metal alloys and x-ray absorption near-edge spectroscopy to measure the electron structure of compressed 3d transition metals.

The Imaging Spectroscopy Snout (ISS) used at the National Ignition Facility is able to simultaneously collect neutron pinhole images, 1D spatially resolved x-ray spectra, and time resolved x-ray pinhole images. To measure the x-ray spectra, the ISS can be equipped with up to four different transmission crystals, each offering different energy ranges from ∼7.5 to ∼12 keV and different resolutions. Characterizing and calibrating such instruments is of paramount importance in order to extract meaningful results from experiments. More specifically, we characterized different ISS transmission-type alpha-Quartz crystals by measuring their responses as a function of photon energy, from which we inferred the angle-integrated reflectivity for each crystal's working reflections. These measurements were made at the Lawrence Livermore National Laboratory calibration station dedicated to the characterization of x-ray spectrometers. The sources used covered a wide x-ray range-from a few to 30 keV; the source diameter was ∼0.6 mm. The experimental results are discussed alongside theoretical calculations using the pyTTE model.

A Cauchois transmission-crystal hard x-ray spectrometer was calibrated by using a portable, compact, battery-powered tungsten x-ray source having 120 peak kilovoltage. The source emission region was characterized by recording high-resolution 2D x-ray images and was found to be composed of three emission regions having a 400 µm overall extent. The absolutely calibrated source fluence was measured by using a calibrated silicon drift detector and was in good agreement with the spectrum calculated by the SpekPy code. High-resolution spectra of the W Kα and Kβ lines in the 57-70 keV energy range were recorded on image plate detectors by the Cauchois spectrometer and provided excellent calibrations of the spectrometer's dispersion and spectral resolution. The minimal effect of the source size in the spectral lines recorded on the spectrometer's Rowland circle and the source-size broadening of the spatial lines recorded well beyond the Rowland circle were analyzed. The integrated reflectivity of the spectrometer's quartz (101) crystal was measured by using the absolutely calibrated 59.318 keV W Kα1 spectral line emission and was in agreement with previous integrated reflectivity measurements performed at the National Institute of Standards and Technology. The well-characterized portable 120 kV x-ray source provides a convenient and cost-effective way to accurately calibrate the sensitivity, dispersion, spectral resolution, and source-size broadening in the spectra recorded by high-resolution x-ray spectrometers operating in the hard x-ray range. The absolutely calibrated source fluence can also be used to calibrate x-ray detectors at energies in the 40-100 keV energy range.

The measurement of gigagauss magnetic fields using Zeeman broadening of Ne-like transitions in highly charged ions in high energy density plasmas is investigated. The transition in Xe44+ from the (2p5 1/23d3/2)J=1 level to the (2p6)J=0 ground level, designated 3C and having 4.858 keV transition energy, is considered in detail. Ne-like Xe spectra were previously recorded from compressed Xe-filled capsules, and the plasma conditions were determined from spectral line ratios and atomic code modeling. Using the Paschen-Back expression for Zeeman broadening produced by strong magnetic fields and the plasma conditions from the compressed Xe-filled capsule experiments to estimate the competing Stark, Doppler, and turbulence broadenings, it is found that >0.34 GG fields can be determined from spectra recorded by a high-resolution spectrometer having 1 eV resolution (5000 resolving power). By scaling the plasma conditions to higher temperatures and densities, the minimum detectable magnetic field is determined for Zeeman broadening of the 3C transition in Ne-like ions up to U82+. Recently developed transmission-crystal spectrometers, employing a cylindrically bent crystal in the Cauchois configuration, have sufficient resolution to determine gigagauss magnetic fields from Zeeman broadening of Ne-like transitions in the 4-18 keV range in Xe44+ to U82+.

A Cauchois-type spectrometer utilizing the (203) lattice planes at an oblique angle of 11.53° to the normal to the surface of a quartz transmission crystal recorded the Kα and Kβ spectral lines of six elements from Fe to Ag in the 6-22 keV energy range from a laboratory x-ray source. After deconvolving the natural lifetime widths and the image plate detector broadening from the observed spectral linewidths, the intrinsic crystal resolving power was determined to be 4000 at the lower energies and decreasing to 1000 at the higher energies. Previously, a Si wafer crystal exhibited twice this resolving power when the (331) planes had been used in asymmetric geometry. The investigation of diffraction with this quartz crystal, with a very similar lattice spacing and therefore spectral coverage, was motivated by the larger integrated reflectivity of quartz due to its well-known quasimosaicity upon elastic bending. The measured spectral linewidths were in good agreement with the widths calculated by accounting for various broadening mechanisms, including source size, crystal thickness, crystal height, crystal rocking curve width, geometrical aberrations, and possible spectrometer configuration errors. This is the first, to the best of our knowledge, demonstration of high resolving power achieved by asymmetric diffraction over a wide energy range (6-22 keV) and with detailed comparisons with theoretical broadenings. Based on these results, Cauchois spectrometers employing asymmetric planes of perfect quartz and silicon crystals can be reliably designed and optimized for high-resolution spectroscopy in the >6  keV energy range.

Development of a new generation of low-groove density-blazed echelle gratings optimized for MIGHTI, a space-borne spatial heterodyne interferometer operating in the visible and near infrared is described. Special demands are placed on the wavefront accuracy, groove profile, and efficiency of these gratings. These demands required a new ruling for this application, with significant improvements over existing gratings. Properties of a new generation of highly efficient, plane gratings with 64  grooves/mm blazed at 8.2° are reported.

An x-ray spectrometer employing a thin (50 μm) silicon transmission crystal was used to record high-resolution Cu Kα spectra from a laboratory x-ray source. The diffraction was from the (331) planes that were at an angle of 13.26° to the crystal surface. The components of the spectral lines resulting from single-vacancy (1s) and double-vacancy (1s and 3d) transitions were observed. After accounting for the natural lifetime widths from reference double-crystal spectra and the spatial resolution of the image plate detector, the intrinsic broadening of the transmission crystal was measured to be as small as 0.67 eV and the resolving power 12 000, the highest resolving power achieved by a compact (0.5 m long) spectrometer employing a single transmission crystal operating in the hard x-ray region. By recording spectra with variable source-to-crystal distances and comparing to the calculated widths from various geometrical broadening mechanisms, the primary contributions to the intrinsic crystal broadening were found to be the source height at small distances and the crystal apertured height at large distances. By reducing these two effects, using a smaller source size and vignetting the crystal height, the intrinsic crystal broadening is then limited by the crystal thickness and the rocking curve width and would be 0.4 eV at 8 keV energy (20 000 resolving power).

A Cauchois type hard x-ray spectrometer was developed that utilizes the (301) diffraction planes at an asymmetric angle of 23.51° to the normal to the surface of a cylindrically curved quartz transmission crystal. The energy coverage is tunable by rotating the crystal and the detector arm, and spectra were recorded in the 8 keV to 20 keV range with greater than 2000 resolving power. The high resolution results from low aberrations enabled by the nearly perpendicular angle of the diffracted rays with the back surface of the crystal. By using other asymmetric planes of the same crystal and rotating to selected angles, the spectrometer can operate with high resolution up to 50 keV.

A unique Compton backscattering configuration for generating monochromatic, short pulse, and potentially coherent x-rays in a Laser Wakefield Accelerator (LWFA) is being studied at the Naval Research Laboratory. Reflection mechanisms such as stimulated Raman scattering and shock-created density gradients in a plasma can generate the required backward-travelling laser pulse directly from the same laser pulse used in the LWFA, i.e., the high energy electron beam and the counter-propagating photon beam are both self-generated by an ultrashort laser pulse in plasma. The automatic alignment of the counter-propagating electrons and photons together with the extended interaction distance and tightly guided beam sizes in a LWFA can lead to a high-gain situation for the Doppler upshifted forward propagating x-rays. Possibilities for exponential gain to achieve coherent generation of the x-rays are investigated. Using 1D warm beam FEL analysis, millimeter gain lengths could be obtained for optimistic energy spread and emittance parameters.

We report on experiments demonstrating the transition from thermally-dominated K-shell line emission to non-thermal, hot-electron-driven inner-shell emission for z pinch plasmas on the Z machine. While x-ray yields from thermal K-shell emission decrease rapidly with increasing atomic number Z, we find that non-thermal emission persists with favorable Z scaling, dominating over thermal emission for Z=42 and higher (hn ≥ 17keV). Initial experiments with Mo (Z=42) and Ag (Z=47) have produced kJ-level emission in the 17-keV and 22-keV Kα lines respectively. We will discuss the electron beam properties that could excite these non - thermal lines. We also report on experiments that have attempted to control non - thermal K - shell line emission by modifying the wire array or load hardware setup.

The tungsten L-gamma transitions between 11 and 12 keV and K alpha transitions from 57 to 60 keV were produced by a laboratory electron-bombarded x-ray source and simultaneously recorded with high resolution by using multiple diffraction planes of the same quartz crystal operating in Cauchois transmission geometry. The W K alpha transitions were dispersed by the (5 0 2) planes, which were perpendicular to the crystal entrance surface, and by the (6 0 2), (7 0 2), and (8 0 4) planes which were rotated with respect to the (5 0 2) planes by angles up to 4.80 degrees. The WL gamma transitions were dispersed by the (2 0 1) planes rotated from the (5 0 2) planes by 4.01 degrees. The spectra from the five planes were simultaneously recorded on image plate detectors, and spectra were also recorded by scanning solid-state electronic detectors with narrow slits across the spectral lines. The metrology of the L and K shell spectra diffracted from multiple quartz planes enabled the detailed analysis of the detector spatial resolution and accurate measurement of the instrumental broadening produced by the various quartz diffraction planes. The W L-gamma spectra had the highest instrumental resolving power, 1800, permitting for the first time the resolution of the blended L-gamma 4' (L1O2) and L-gamma 4 (L1O3) transitions. After subtracting the instrumental and detector contributions to the line widths, the remainder was assigned to the natural line widths. The measured widths of the O2 and O3 levels were 2.9 eV and 1.9 eV, respectively, and based on atomic code calculations these widths are attributed to the O2O3O4 and O3O4O5 super Coster-Kronig processes. This work demonstrates the ability to simultaneously record high resolution (< 1 eV) L and K spectra to determine the line shapes of the heavy elements (e.g. W through Am) by using multiple planes of a single quartz crystal and to accurately measure the non-radiative super Coster-Kronig rates which are closely related to the energy level structure of the outer shells of the heavy elements.

Ultra-thin curved transmission crystals operating in the Cauchois spectrometer geometry were evaluated for the purpose of achieving high spectral resolution in the 6-13 keV x-ray energy range. The crystals were silicon (111) and sapphire R-cut wafers, each 18 μm thick, and a silicon (100) wafer of 50-μm thickness. The W Lα(1) spectral line at 8.398 keV from a laboratory source was used to evaluate the resolution. The highest crystal resolving power, E/ΔE=6300, was achieved by diffraction from the (33-1) planes of the Si(100) wafer that was cylindrically bent to a radius of curvature of 254 mm, where the (33-1) planes have an asymmetric angle of 13.26° from the normal of the crystal surface facing the x-ray source. This work demonstrates the ability to measure highly resolved line shapes of the K transitions of the elements Fe through Kr and the L transitions of the elements Gd through Th using a relatively compact spectrometer optical system and readily available thin commercial wafers. The intended application is as a diagnostic of laser-produced plasmas where the presence of multiple charged states and broadenings from high temperature and density requires high-resolution methods that are robust in a noisy source environment.

Betatron x-ray spectra in the 10 keV to 70 keV energy range were recorded by a transmission crystal spectrometer. This work demonstrates for the first time the ability to accurately measure the absolutely-calibrated betatron photon energy distribution using a high-resolution wavelength dispersive crystal spectrometer. The betatron emission was generated by the interaction of intense pulses from the Rutherford Appleton Laboratory Astra-Gemini laser with a gas capillary waveguide. The spectrometer utilized a quartz (101) crystal that was cylindrically bent to a radius of 112 mm.1 The crystal was positioned 2.5 m from the photon source and covered a 12.6 mrad by 9.3 mrad field of view. Single and multiple shot spectra were recorded on an image plate detector. After subtracting the background resulting from energetic (> 300 keV) scattered photons, the energy-dependent shape of the spectrum and the absolute number of photons were measured using the crystal efficiency and image plate calibration curves. The experimental spectra in units of photons/keV/mrad2, averaged over the spectrometer's field of view, were in good agreement with the synchrotron energy distribution. For optimal laser and betatron generation conditions, the fluence of photons having energies > 10 keV was about 3×104 photons/mrad2 per shot, and the critical energy of the fitted synchrotron distribution was 8.8 keV ± 0.5 keV. To further understand and optimize the betatron generation process, it will be necessary to measure the betatron photon distribution with increased accuracy and also with angular resolution in the laser polarization direction and perpendicular to this direction. Improved instrument accuracy and sensitivity can be accomplished by utilizing thicker shielding and improved baffling to reduce the background resulting from > 300 keV scattered photons. Owing to the Bragg condition that must be satisfied along the length of the bent crystal, spectral images present angular and energy dependence in the dispersion plane. Angular resolution in the orthogonal, out-of-plane direction occurs because the fan of x-rays from the small (effectively point) source passes through the crystal with small deflection and is projected onto the image plate.

We report on the generation of bright multi-keV betatron X-ray radiation using a GeV laser wakefield accelerator and investigate the use of these X-rays for various imaging applications.

Spectra of the W L transitions in the energy range 8-12 keV from warm dense plasmas generated by the Naval Research Laboratory's Gamble II pulsed power machine were recorded by a newly developed high-resolution transmission-crystal X-ray spectrometer with +/-2 eV accuracy. The discharges have up to 2 MV voltage, 0.5 MA current, and produce up to 2.4 MJ/cm(-3) energy density. The plasma-filled rod pinch (PFRP) diode produces a plasma with N-e approximate to 10(22) cm(-3) and T-e approximate to 50 eV during the time of maximum X-ray emission. By analyzing the line shapes, it was determined that the L beta(2) inner-shell transition from the 4d(5/2) level was shifted to higher energy by up to 23 eV relative to nearby L beta transitions from n = 3 levels. In addition, the L beta(2) transition was significantly broader and asymmetric compared to the n = 3 transitions. The energy shift of the L beta(2) transition results from the ionization of electrons outside the 4d shell that perturbs the transition energies in the ions to higher values. The increased line width and asymmetry result from unresolved transitions from a range of ionization states up to +28. The ionization distribution was determined by comparison of the measured energy shifts and widths to calculated transition energies in W ions, and the ionization was correlated with Gamble discharge parameters such as the anode type and the high voltage delay time. This work demonstrates a new hard X-ray spectroscopic diagnostic technique for the direct measurement of the ionization distribution in warm dense plasmas of the heavy elements W through U that is independent of the other plasma parameters and does not require interpretation by hydrodynamic, atomic kinetics, and radiative simulation codes. (C) 2013 Elsevier B.V. All rights reserved.

The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (lambda = 248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (lambda = 351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns <= tau <= 1.25 ns) and intensities (up to 2 x 10(15) W/cm(2)). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789379]