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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.

Spectra of the W L transitions in the energy range 8e12 keV from warm dense plasmas generated by theNaval Research Laboratory’s Gamble II pulsed power machine were recorded bya newly developed high-resolution transmission-crystal X-ray spectrometer with 2 eV accuracy. The discharges have up to 2 MVvoltage, 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 z 10 22 cm 3 and T e z 50 eV during the time of maximum X-rayemission. By analyzing the line shapes, it was determined that the L b 2 inner-shell transition from the4d 5/2 level was shifted to higher energy by up to 23 eV relative to nearby L b transitions from n ¼ 3 levels.In addition, the L b 2 transition was significantly broader and asymmetric compared to the n ¼ 3 transi-tions. The energy shift of the L b 2 transition results from the ionization of electrons outside the 4d shellthat perturbs the transition energies in the ions to higher values. The increased line width and asym-metry result from unresolved transitions from a range of ionization states up to þ28. The ionizationdistribution was determined by comparison of the measured energy shifts and widths to calculatedtransition energies in W ions, and the ionization was correlated with Gamble discharge parameters suchas the anode type and the high voltage delay time. This work demonstrates a new hard X-ray spectro-scopic diagnostic technique for the direct measurement of the ionization distribution in warm denseplasmas of the heavy elements W through U that is independent of the other plasma parameters anddoes not require interpretation by hydrodynamic, atomic kinetics, and radiative simulation codes. 2013 Elsevier B.V. All rights reserved.

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 ...

Photon spectra in the energy range 60 keV to 1 MeV were recorded from targets irradiated by the LLNL Titan and LLE EP picosecond lasers. The radiation consisted of K-shell radiation, bremsstrahlung radiation from MeV electrons, and preliminary evidence for 511 keV positron annihilation radiation. The spectra were recorded by two instruments, an energy-dispersive CCD detector with a CsI phosphor coating that operated in the single-hit per pixel mode and was absolutely calibrated using a Cs-137 662 keV source, and a wavelength-dispersive Cauchois type spectrometer employing a curved Ge(220) transmission crystal that operated in the first and second diffraction orders with high spectral resolution. The calibrated photon energy distributions from Au, Eu, and Al targets are compared to the energetic electron distributions emerging from the targets.

The production of X-rays from electron transitions into K-shell vacancies (Kα,β) emission) is a well-known process in atomic physics and has been extensively studied as a plasma diagnostic in low- and mid-Z materials. However, X-ray spectra from near neutral high-Z ions are very complex, and their interpretation requires the use of state-of-the-art atomic calculations. In this experiment, the Titan laser system at Lawrence Livermore National Laboratory was used to deliver an approximately 350 J laser pulse, with a 10 ps duration and a wavelength of 1054 nm, to a gold (Au) target. A transparent bent quartz crystal spectrometer with a hard X-ray energy window, ranging from 17 to 102 keV, was used to measure the emission spectrum. Kα1,α2 and Kβ1,γ1 transitions were observed over a range of target sizes. Additionally, a series of shots were conducted with a pre-ionizing long pulse (3 ns, 1–10 J, 527 nm) on the backside of the target. FLYCHK, an atomic non-LTE code, designed to provide ionization and population distributions, was used to model the experiment. Kα/Kβ ratios were found to be in good agreement with the predicted value for room temperature Au targets.

A new spectroscopic technique for the measurement of the sizes of hard X-ray sources produced by the irradiation of solid-density targets by intense laser radiation is discussed. The technique is based on the source broadening of K shell spectral lines from targets irradiated by intense picosecond laser pulses. The spectra are recorded by a modified Cauchois type spectrometer, where the detector is placed far behind the Rowland circle where source broadening dominates instrumental resolution. The laser irradiation with focused intensity greater than 10 18 W/cm 2 produces relativistic electrons that propagate from the focal spot into the surrounding target material with mm range. The energetic electrons produce 1 s electron ionization and K shell radiation with picosecond duration that can be utilized for transient radiography of dense objects including evolving dense plasmas. However, the hard X-ray source has mm lateral size when extended targets are utilized while a much smaller source size (of order 10 μm) is necessary for high-resolution point projection radiography. The lateral source size can be greatly reduced by using targets with limited aspect to the radiography object such as thin foils and wires, but the brightness of these sources is greatly reduced compared to thick planar targets. Studies indicate that the electron range and source size can also be reduced by utilizing an electrically resistive target material such as teflon. In this case the electron propagation from the focal spot is inhibited by a weak return current and incomplete space–charge neutralization. These experimental results are important not only for producing a small hard X-ray source for picosecond radiography but also for reducing the lateral propagation of energetic electrons that can be detrimental to fast-ignition fusion.

A formidable array of advanced laser systems are emerging that produce extreme states of light and matter. By irradiating solid and gaseous targets with lasers of increasing energy densities, new physical regimes of radiation effects are being explored for the first time in controlled laboratory settings. One result that is being accomplished or pursued using a variety of techniques, is the realization of novel sources of X-rays with unprecedented characteristics and light–matter interactions, the mechanisms of which are in many cases still being elucidated. Examples include the megajoule class of laser-produced plasmas designed in pursuit of alternative-energy and security applications and the petawatt class of lasers used for fast ignition and X-ray radiographic applications such as medical imaging and real-time imaging of plasma hydrodynamics. As these technologies mature, increased emphasis will need to be placed on advanced instrumentation and diagnostic metrology to characterize the spectra, time structure, and absolute brightness of X-rays emitted by these unconventional sources. Such customized and absolutely calibrated measurement tools will serve as an enabling technology that can help in assessing the overall system performance and progress, as well as identification of the underlying interaction mechanisms of interest to basic and applied strong-field and high-energy-density science.

The propagation of energetic electrons from the focal spots of intense picosecond laser pulses was studied using targets consisting of planar foils and fine metal wires. High-resolution K-shell spectra of elements with atomic numbers in the range 46–74 (Pd to W) and with energies from 21 keV to 69 keV were recorded by a Cauchois-type spectrometer using a curved transmission crystal. The K-shell spectra resulted from the collisional ionization of 1 s electrons by energetic electrons that were generated in the laser focal spot and propagated into the planar foil region beyond the focal spot or into the metal wires adjacent to an irradiated wire. The lateral spread of the energetic electrons from the focal spot was determined from the source broadening of the K spectral lines and from the relative intensities of the K spectra from an irradiated wire and neighboring wires of different metals. The propagation distances up to 1 mm in a variety of materials indicated electron energies up to 1 MeV were generated in the laser focal spot. Inhibited propagation in an electrically insulating material was observed that results from a weak return current and incomplete space charge neutralization.

Conversion efficiencies of laser light into K x-ray radiation are used to characterize laser-solid interactions e.g. in measurements with back-lighter targets in Inertial Confinement Fusion research or in ultra short x-ray science where ultra short laser pulses are used to create x-rays for investigation of dynamic processes. In our measurements we observed high energy (few tens of keV) K x-ray radiation of element pairs created upon impact of a 1 ps, 100 J laser pulse on the target surface. The high-energy electrons created in this interaction ionise and excite the target material. We have used high purity alloy foils of Pd and Ag, as well as In and Sn and crystals of CsI and rare earth molybdates as target materials. Both constituents of these targets were simultaneously excited in one shot. The K x-ray radiation was dispersed and detected with the LCS (LULI Crystal Spectrometer), a Cauchois-type cylindrically bent transmission-crystal spectrometer. Measuring ratios in the x-ray spectra permits determination of relative conversion efficiencies for pairs of elements under identical laser-target interaction conditions.

We present spectral line wavelengths, identifications, and intensities in the 171-211 and 245-291 A ranges from five solar plasma regions recorded by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on Hinode. The recorded data were emitted from a quiet region, two active areas on the solar disk, a limb region, and a region 20'' above the limb. The line list contains 500 lines of which 55% were identified with previously known transitions. Although the EIS spectral coverage is limited to two ranges approximately 40 A wide, the identified lines belong to a total of 56 ions from 15 elements.

A wavelength calibration of solar lines observed by the high resolution EUV Imaging Spectrometer (EIS) on the Hinode satellite is reported. Spectral features of the quiet sun and of two mildly active areas were measured and calibrated. A listing of the stronger observed lines with identification of the leading contributor ions is presented. 41 lines are reported, with 90% identified. Wavelength precisions (2{sigma}) of {+-}0.0031 Angstroms for the EIS short band and {+-}0.0029 Angstroms for the EIS long band are obtained. These lines, typical of 1-2x10{sup 6} K plasmas, are recommended as standards for the establishment of EIS wavelength scales. The temperature of EIS varies by about 1.5 C around the orbit and also with spacecraft pointing. The correlation of these temperature changes with wavelength versus pixel number scale changes is reported.

High temperature (“hot”) hohlraums are being developed to heat samples to high temperatures for opacity or other atomic physics studies. Hot hohlraums have been fielded at the National Ignition Facility [D.E. Hinkel, et al., Phys. Plasmas 12 (2005) 056305] and the OMEGA [M.B. Schneider, et al., Phys. Plasmas 13 (2006) 112701] lasers. They reach high radiation temperatures by coupling a maximum amount of laser energy (10 kJ) into small, i.e., 400–800 μm diameter, gold hohlraums in a 1 ns pulse causing the hohlraums to fill with gold plasma. Radiation temperatures of 370 eV have been measured in the laser entrance hole (LEH) region of these targets [D.E. Hinkel, et al., Phys. Rev. Lett. 96 (2006) 195001]. However, the LEH radiation is not the radiation drive of interest as the sample can neither be shielded from the non-thermal components of this radiation nor protected from the gold plasma. To mitigate these problems the source we are developing uses the radiation from the X-ray burnthrough of thin walls of a pair of hot hohlraums to heat a sample. We report on the measured radiation drive of this source and its use to heat a surrogate sample. We characterize the radiative heating of the sample by measuring its thermal expansion.

K-shell X-ray spectra were recorded by the Dual Crystal Spectrometer (DCS) from Ag, Sn, Sm, Ta, and Au planar foil targets irradiated by single intense femtosecond pulses from the Titan laser at Lawrence Livermore National Laboratory. DCS implements two quartz crystals in transmission (Laue) geometry covering the X-ray energy range 10–50 keV and 20–120 keV. The spectral images were recorded on photo-stimulable phosphor image plates and on film/phosphor cassettes. The Kα and Kβ spectral lines of Ag with energies 22 keV and 25 keV, Sn at 25 keV and 28 keV, Sm at 40 keV and 46 keV, Ta at 57 keV and 66 keV, and Au at 67 keV and 79 keV were clearly resolved. The observation of these spectral lines, resulting from 1s electron vacancies created by electrons with energies up to at least 80 keV, enables the implementation of K-shell spectroscopy diagnostic techniques for understanding the laser energy deposition, energetic electron generation, ionization distribution, and X-ray conversion efficiency in plasmas produced by an intense femtosecond laser pulse. Based on the measured energies of the Au K-shell transitions, we conclude that the observed Au K-shell transitions are from ionization stages lower than Au+44, and are most likely from neutral Au atoms, that the Titan plasmas and the hard X-ray emissions are dominated by electrons with energies exceeding 80 keV, and that thermal processes play a minor role.

The EUV Imaging Spectrometer (EIS) on Hinode will observe solar corona and upper transition region emission lines in the wavelength ranges 170 – 210 A and 250 – 290 A. The line centroid positions and profile widths will allow plasma velocities and turbulent or non-thermal line broadenings to be measured. We will derive local plasma temperatures and densities from the line intensities. The spectra will allow accurate determination of differential emission measure and element abundances within a variety of corona and transition region structures. These powerful spectroscopic diagnostics will allow identification and characterization of magnetic reconnection and wave propagation processes in the upper solar atmosphere. We will also directly study the detailed evolution and heating of coronal loops. The EIS instrument incorporates a unique two element, normal incidence design. The optics are coated with optimized multilayer coatings. We have selected highly efficient, backside-illuminated, thinned CCDs. These design features result in an instrument that has significantly greater effective area than previous orbiting EUV spectrographs with typical active region 2 – 5 s exposure times in the brightest lines. EIS can scan a field of 6×8.5 arc min with spatial and velocity scales of 1 arc sec and 25 km s−1 per pixel. The instrument design, its absolute calibration, and performance are described in detail in this paper. EIS will be used along with the Solar Optical Telescope (SOT) and the X-ray Telescope (XRT) for a wide range of studies of the solar atmosphere.

The inertial confinement fusion community is actively preparing for the transition from kilojoule- to megajoule-class lasers. To assess laser and target performance, a sophisticated array of diagnostics that can operate in increasingly harsh environments is required. In this paper, we overview some of the needs and challenges related to performing X-ray spectroscopy with very intense and highly energetic X-ray sources. To illustrate issues that will be broadly applicable to diagnostics at high energy density facilities, we relate lessons learned during early testing of the high-energy electronic X-ray spectrometer (HENEX), a core-level diagnostic commissioned by the National Ignition Facility. A spectrometer design employing symmetric Laue diffraction has proven to be particularly well suited for the high energy density environment and will extend existing diagnostic techniques to high-Z, K-shell spectroscopy.

X-ray diagnostics in today's high-energy density environments must contend with intense and energetic X-ray background levels. In this work, we address the issues of X-ray fluorescence and scattering in reflection-geometry X-ray crystal spectrometers. In this geometry, the detector can capture not only a dispersed X-ray spectrum but also fluorescence and/or scattered X-rays from the diffracting crystal and crystal mounts. Studies to optimally reduce these sources of spectral contamination have been performed using the HENEX spectrometer. Variables that mitigate such unwanted background include filtration, collimation and judicious selection of crystal and detector materials.

Outstanding discrepancies between data and calculations of laser-produced plasmas in recombination have been observed since the 1980s. Although improvements in hydrodynamic modeling may reduce the discrepancies, there are indications that non-LTE atomic kinetics may be the dominant cause. Experiments to investigate non-LTE effects were recently performed at the NIKE KrF laser on low-density Ti-doped aerogels. The laser irradiated a 2 mm diameter, cylindrical sample of various lengths with a 4-ns square pulse to create a volumetrically heated plasma. Ti L-shell spectra spanning a range of 0.47–3 keV were obtained with a transmission grating coupled to Si photodiodes. The diagnostic can be configured to provide 1-dimensional spatial resolution at a single photon energy, or 18 discrete energies with a resolving power, λ / δ λ of 3–20. The data are examined and compared to calculations to develop absolute emission measurements that can provide new tests of the non-LTE physics.

High-resolution X-ray spectra were recorded by the High-Energy Electronic X-ray (HENEX) spectrometer from a variety of targets irradiated by the Omega laser at the Laboratory for Laser Energetics. The HENEX spectrometer utilizes four reflection crystals covering the 1–20 keV energy range and one quartz(1 0 −1 1) transmission crystal (Laue geometry) covering the 11–40 keV range. The time-integrated spectral images were recorded on five CMOS X-ray detectors. In the spectra recorded from krypton-filled gasbag and hohlraum targets, the helium-like K-shell transitions n = 1 – 2 , 1–3, and 1–4 appeared in the 13–17 keV energy range. A number of additional spectral features were observed at energies lower than the helium-like n = 1 – 3 and n = 1 – 4 transitions. Based on computational simulations of the spectra using the FLYCHK/FLYSPEC codes, which included opacity effects, these additional features are identified to be inner-shell transitions from the Li-like through N-like krypton charge states. The comparisons of the calculated and observed spectra indicate that these transitions are characteristic of the plasma conditions immediately after the laser pulse when the krypton density is 2×1018 cm−3 and the electron temperature is in the range 2.8–3.2 keV. These spectral features represent a new diagnostic for the charge state distribution, the density and electron temperature, and the plasma opacity. Laboratory experiments indicate that it is feasible to record K-shell spectra from gold and higher Z targets in the >60 keV energy range using a Ge(2 2 0) transmission crystal.

Responsivity of silicon photodiodes was measured from -100 C to +50 C in the 3 to 250 nm wavelength range using synchrotron and laboratory radiation sources. Two types of silicon photodiodes were studied, the AXUV series having a thin nitrided silicon dioxide surface layer and the SXUV series having a thin metal silicide surface layer. Depending on the wavelength, the responsivity increases with temperature with the rates 0.013%/C to 0.053%/C for the AXUV photodiode and 0.020%/C to 0.084%/C for the SXUV photodiode. The increase in responsivity is consistent with the decrease in the silicon bandgap energy which causes a decrease in the pair creation energy. These results are particularly important for dose measurement in extreme ultraviolet (EUV) lithography steppers and sources since the detector temperature often increases because of the high EUV intensities involved.

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.

Hard X-ray spectra from laser-produced plasmas were recorded by a transmission crystal survey spectrometer covering the 12– 60 keV energy range with a resolving power of E/ΔE≅100. This emission is of interest for the development of hard X-ray backlighters and hot electron diagnostics. Foils of U and Pb were irradiated at the OMEGA laser facility by 24 beams (12 on each side), each with an energy of ≅500 J , a pulse duration of 1 ns , and no beam smoothing. The beams were focused to a 50 μm diameter spot on the target plane. The spectra typically exhibit a few intense and relatively narrow features in the 12– 22 keV energy range. Initial analysis suggests that these hard X-ray features are inner-shell transitions resulting from L-shell vacancies created by energetic electrons. The observed transition energies are slightly higher than the neutral-atom characteristic X-ray energies. Calculations suggest that the transitions are in the Ni-like or lower ionization stages. The analysis further indicates that opacity effects play an important role in producing the spectra.

A new x-ray diagnostic has been commissioned at the OMEGA laser facility at the University of Rochester. It is a transmission curved crystal spectrometer designed primarily to characterize the hot-electron energy distribution of laser generated plasmas by registering the continuum x-ray spectrum produced by these hot plasmas from 12 to 60 keV. The diagnostic package is assembled in a linear configuration to ride in a standard instrument insertion module. The instrument consists of a nosecone with a blast shield, spectrometer, electronic imager, drive electronics, and battery. The instrument is connected to the external diagnostic processor and control unit by trigger and data fiber optic cables. Time integrated spectra from various targets have been registered with high sensitivity from single shots of the OMEGA laser.

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.

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.

Hard x-ray tungsten spectra from the NRL Gamble II generator were recorded by a transmission crystal spectrometer in the photon energy range > 10 keV.1 The crystal diffraction efficiencies were accurately calibrated,2 and this enables the accurate measurement of the absolutely-calibrated photon energy distribution from pulsed power generators. When measuring spectra in the 20 to 70 keV range, which is of interest for x-ray damage studies, the Gamble II experiments demonstrated the need to shield against higher energy photons up to the peak kilovoltage of the pulsed-power generator. In addition, a spectrometer optimized for measuring the x-ray fluence should be able to record the photon energy distribution from the entire area of a wide x-ray source on a single discharge. A new spectrometer has been designed that can record the absolutely-calibrated 20–70 keV photon energy distribution from a 12” diameter source such as produced by the Saturn generator. The spectra from the left and right sides of the source are spatially resolved on the detector, and a slot aperture provides spatial resolution in the perpendicular direction. The spectrometer can be deployed at standoff distances in the 2 to 4 meter range and can record the spatially resolved spectra from a single discharge on an image plate detector. The spectrometer has a linear geometry with a central axis, and the spectrometer is easily aligned using a laser propagating along the central axis and pointing to the center of the x-ray source. Spectrometers of this type have been custom designed for recording hard x-ray spectra at short-pulse laser facilities with shielding against MeV photons, and the same shielding techniques can be applied to recording spectra from energetic pulsed-power generators. Using an absolutely calibrated x-ray source at NIST, the individual spectrometer components such as crystal and filters can be calibrated to few percent accuracy. The spectrometer's final end-to-end sensitivity calibration, which relates the detector signal to the source fluence, can be performed to better than 20% absolute accuracy. Such accurate measurement of the x-ray fluence from pulse-power generators will greatly improve the analysis and mitigation of x-ray irradiation damage.

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. © 2014 Optical Society of America.

A National Ignition Facility (NIF) core diagnostic instrument has been designed and will be fabricated to record x-ray spectra in the 1.1–20.1 keV energy range. The High-Energy Electronic X-Ray (HENEX) instrument has four reflection crystals with overlapping coverage of 1.1–10.9 keV and one transmission crystal covering 8.6–20.1 keV. The spectral resolving power varies from approximately 2000 at low energies to 300 at 20 keV. The spectrum produced by each crystal is recorded by a modified commercial dental x-ray charge coupled device detector with a dynamic range of at least 2500.

The Nike KrF laser, with its very uniform focal distributions, has been used at intensities near 10 14 W/cm 2 to launch shock waves in polystyrene targets. The rear surface visible light emission differed between clear polystyrene (CH) targets and targets with a thin (125 nm) Al coating on the rear side. The uncoated CH targets showed a relatively slowly rising emission followed by a sudden fall when the shock emerges, while the Al-coated targets showed a rapid rise in emission when the shock emerges followed by a slower fall, allowing an unambiguous determination of the time the shock arrived at the rear surface. A half-aluminized target allowed us to observe this difference in a single shot. The brightness temperature of both the aluminized targets and the non-aluminized targets was slightly below but close to rear surface temperature predictions of a hydrodynamic code. A discussion of preheat effects is given.

Nike is a multi-kilojoule KrF laser with very high beam uniformity (ΔI/I< 0.2% with all 36 overlapped beams), and the capability to accelerate relatively thick targets on a low adiabat under conditions scalable to direct drive ICF. In a first set of experiments we determined the effect of the imprinting by varying the uniformity of the foot of the laser pulse and measuring the growth of the subsequent Rayleigh-Taylor instability. We found that the lower the imprint, the longer the mass modulations take to reach a given level. This is in quantitative agreement with our 2-D hydrodynamics simulations. The results are promising for direct drive with a very uniform laser.

The main goal of this paper is to present experimental results on comparison of lasing efficiency for Li III 13.5 nm (2-1 transition) line in LiF microcapillary plasmas using 0.25 and 1 /spl mu/m subpicosecond pumping lasers. A formula for soft X-ray laser efficiency calculation is presented and used for such comparisons. The results for discharge created preplasma in L=4 mm and L=14 mm microcapillaries are also presented and compared with the results for laser created preplasma.

An EUV spectral range of less than 100 A in first order has been found that includes sufficient spectral lines and critical combinations of lines in first and second order to permit dynamic and diagnostic investigations of the solar atmosphere with a relatively simple spectrometer. An optical design of such a spectrometer, based on the performance of the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft, and sample stigmatic solar spectra for the range 1334-1428 A from SUMER are presented to illustrate the utility of this range. Lines of almost all abundant solar elements except H and He are present within this wavelength band in first or second order. The lines cover the large temperature range from 1 × 104 K (chromosphere) to 2 × 107 K (flares). The spectrometer's resolution is sufficiently high to permit measuring line profiles and wavelength shifts which allows plasma dynamical studies of individual solar structures from the chromosphere up into the corona. In addition, electron density diagnostics are available within the spectral range that cover the temperature range from 8 × 104 to 1 × 106 K and an electron density range from 108 to 1013 cm-3.

A portable hard x-ray source has been developed for nondestructive testing, medical imaging, and flash x-ray radiography. The source is powered by a Marx generator that produces a 200 kV, 1.2 kA pulse of 60 ns full width at half maximum. The x-ray tube is composed of a tungsten anode and a mesh cathode. The time dependence of the voltage, current, and x-ray emission were measured and were in good agreement with computer simulations. The simulation model accounted for the 15 capacitors and 15 spark gap switches of the Marx generator and the perveance of the electron flow across the anode–cathode gap. The simulations indicated that the 5 J energy that was stored in the Marx generator was efficiently delivered to the x-ray tube. The measured x-ray exposure, 34 mR at a distance of 30 cm, was in good agreement with the calculated exposure. X-ray images are presented that demonstrate the capabilities of the x-ray source for medical imaging, nondestructive testing, and flash x-ray radiography.

Underdense radiation sources have been developed to provide efficient laboratory multi-keV radiation sources for radiography and radiation hardening studies. In these plasmas laser absorption by inverse bremsstrahlung leads to high x-ray conversion efficiency because of efficient ionization of the low density aerogel or gas targets. Now we performing experiments in the soft x-ray energy regime where the atomic physics models are much more complicated. In recent experiments at the NIKE laser, we have irradiated a Ti-doped SiO 2 aerogel with up to 1650J of 248 nm wavelength light. The absolute Ti L-shell emission in the 200-800 eV range is measured with a diagnostic that uses a transmission grating coupled to Si photodiodes. We will give an overview of the temporally-resolved absolutely calibrated spectra obtained over a range of conditions. Eventually we hope to extend our studies to x-ray production in the EUV range.

The Nike laser group at the Naval Research Laboratory has an ongoing effort to improve and benchmark the radiation hydrodynamic simulations used to develop pellet designs for inertial confinement fusion. A new postprocessor, Virtual Spectro, has been added to the FAST code suite for detailed simulation of non-LTE spectra, including radiation transport effects and Stark line profile. This new combination enhances our ability to predict the absolute emission of soft x-rays. An absolutely calibrated transmission grating spectrometer and a high resolution grazing incidence spectrometer have been used to collect time integrated and time resolved spectra emitted by CH targets irradiated at laser intensities of ∼ 10 TW/cm 2 . Comparison between these observations and simulations using Virtual Spectro demonstrates excellent agreement (within factor of ∼ 1.5) for the absolute emission.

Plastic foils were irradiated by the NRL Nike KrF laser and were imaged in the x-ray and extreme ultraviolet regions with 2D spatial resolution in the 3–10 μm range. The CH foils were backlit by a silicon plasma. The silicon backlighter emission was recorded by an x-ray spectrometer, and the Si+12 1,865 eV resonance line emission was recorded by a fast x-ray diode. A spherically curved quartz crystal produced monochromatic images of the 1,865 eV radiation that was transmitted by the CH foils. Instabilities that were seeded by linear ripple patterns on the irradiated sides of CH foils were observed. The ripple patterns had periods in the 31–125 μm range and amplitudes in the 0.25–5.0 μm range.

X-ray spectra from Molybdenum plasmas were recorded by a Cauchois-type cylindrically bent Transmission Crystal Spectrometer (TCS). The absolutely calibrated spectrometer provides an unprecedented resolution of inner shell transitions (K x-ray radiation). This tool allows us to resolve individual lines from different charge states existing inside the laser-produced plasma. The inner shell transitions from highly charged Molybdenum shown in this report have never been resolved before in such detail in a laser-produced plasma.

The x‐ray emission from plasmas created by the Naval Research Laboratory Nike KrF laser [Phys. Plasmas 3, 2098 (1996) ] was characterized using imaging and spectroscopic instruments. The laser wavelength was 1/4 μm, and the beams were smoothed by induced spatial incoherence (ISI). The targets were thin foils of CH, aluminum, titanium, and cobalt and were irradiated by laser energies in the range 100–1500 J. A multilayer mirror microscope operating at an energy of 95 eV recorded images of the plasma with a spatial resolution of 2 μm. The variation of the 95 eV emission across the 800 μm focal spot was 1.3% rms. Using a curved crystal imager operating in the 1–2 keV x‐ray region, the density, temperature, and opacity of aluminum plasmas were determined with a spatial resolution of 10 μm perpendicular to the target surface. The spectral line ratios indicated that the aluminum plasmas were relatively dense, cool, and optically thick near the target surface. The absolute radiation flux was determined at 95 eV and in x‐ray bandpasses covering the 1–8 keV region. The electron temperature inferred from the slope of the x‐ray flux versus energy data in the 5–8 keV region was 900 eV for an incident laser energy of 200 J and an intensity of ≊1013 W/cm2.

A spherical holographic ion-etched diffraction grating with low-blaze angle has been purchased for the purpose of vendor evaluation. We present the results of surface measurements made on the bare grating substrate using an atomic force microscope. The efficiency of the grating at grazing incidence and at EUV wavelengths was measured using a synchrotron light source. After coating the grating with a multilayer, the normal incidence efficiency was measured. The results of these measurements are compared to those obtained from samples from other vendors.

Instruments incorporating normal-incidence mirrors and gratings have been used to record images and spectra in the extreme u.v. and soft x-ray regions. The multilayer coatings were optimized to reflect wavebands of interest for the diagnosis of dense plasmas. Images at wavelengths of 33.8 and 130 A were recorded with spatial resolution of 5 μm. Using normal-incidence multilayer gratings operating in the wavelength region 130–300 A, spectra with resolution of 14,000 were recorded which allows the use of line profiles to determine Doppler plasma motion an Stark densities. Because of the high throughput of the multilayer optics, the instruments can be located at large distances from the plasmas, and the optics were undamaged by the intense radiation and debris fluxes from laser-produced plasmas. The absolute radiation flux was determined at wavelengths of 33.8 and 130 A.

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 high-resolution x-ray spectrometer utilizing a thin quartz transmission crystal and covering the 6 keV-18 keV energy range has been developed and tested. The spectrometer consists of a cylindrically bent crystal in a vacuum housing. The crystal position and the range of Bragg angles that are incident on the crystal can be adjusted to record an ≈4 keV wide spectrum in the 6 keV-18 keV range. The spectrometer is of the Cauchois type and has a compact linear geometry that is convenient for deployment at laser-produced plasma, EBIT, and other x-ray sources. Test spectra of the W L and Mo K lines from laboratory sources have linewidths as small as 11 eV, approaching the natural widths, and instrumental resolving power as high as 1800. Techniques for enhancing the energy resolution are experimentally demonstrated.

A space-resolved electron density diagnostic of a holmium laser-produced plasma has been performed using the intensity ratios of Cu I--like 3[ital d][sup 10]4[ital l]-3[ital d][sup 10]4[ital l][prime] lines. The atomic theoretical model of the Cu I--like ion included the 3[ital d][sup 10][ital nl] levels with [ital n]=4,5 and [ital l]=[ital s],[ital p],[ital d],[ital f]. The effect of line absorption at high electron densities is discussed and the atomic data obtained with the HULLAC computer code are compared with previously published data.

High-resolution absorption spectra of radiatively-heated low-Z foils (CH and BN) have been recorded at the Nova II laser facility by a grazing-incidence spectrograph. Using a calibration curve for Kodak 101 photographic plates, the plate density was converted to relative intensity transmitted by the foil. Absorption spectra are presented for the elements B, C, and N. The absorption features near the nickel L edge in the wavelength region 11–15 A are also presented.

We review recent experimental results on the path to producing electron-positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 1016 cm-3 and 1013 cm-3, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 1018 cm-3, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter. © 2011 Elsevier B.V.

A zone plate composed of Mo zones having 4 mm outermost zone diameter, 100 nm outermost zone width, and supported on a silicon nitride membrane was characterized using monochromatic synchrotron radiation in the 2 to 20 nm wavelength range. The zero and first order efficiencies were measured and compared to ab initio calculations that account for the optical properties of the materials, the width and shape of the zones, and multiple-layer thin-film effects. It is shown that the thicknesses of the Mo zones and the membrane and the ratio of the zone width to zone period can be independently determined from the measured diffraction efficiencies in the zero and first orders and that the computational code can be used to reliably design zone plates that are optimized for applications such as solar irradiance monitors in the extreme ultraviolet region.

In an ionized atom the Kα and Kβ fluorescence lines have different, and usually slightly higher, energies than the same lines in a cold, un-ionized atom. The increase in fluorescence line energy Δ(hv) that pulsed power discharges can produce in high atomic number atoms is usually much smaller than the line energies hv themselves: typical numbers are hv = 60 keV and Δ(hv) = 10–20 eV, while the resolution obtained so far with a transmission crystal spectrometer developed for the purpose is around 100 eV. Hence any change in the energy of the fluorescence x-rays, from tungsten weakly ionized in the tungsten of the Plasma-Filled Rod Pinch (PFRP), could not be observed.

The efficiency of an ion-etched blazed holographic grating was measured by the use of synchrotron radiation in the 125–133-A wavelength range and at near-normal incidence. The grating had a Mo–Si multilayer interference coating that resulted in a peak normal-incidence efficiency of 13% in the second grating order and at a wavelength of 128 A. This is the highest efficiency obtained to date from a multilayer-coated grating in this wavelength region and at normal incidence. These measurements are compared with similar measurements performed on the same grating 4.5 years later. Over this time the peak grating efficiency decreased from 13% to 8%, and this result is attributed to the decrease in the reflectance of the multilayer coating from 55% to 42%. Oxidation and contamination of the multilayer with carbon appear to be the causes of these losses. The groove efficiency of the grating substrate in the second order is 23%.