Search

The photoefficiency of CsI and CuI photocathodes was measured for photons in the 22–240-eV (50–560-A) energy range. The within-batch and batch-to-batch variation in photoefficiency were studied as was the sensitivity of the samples to storage under dry nitrogen. The effect of exposure to air was investigated. The shape of the photoefficiency curves was found to agree quite well with that expected from the photoabsorption cross sections of the materials. CsI in particular appears useful as a detector in soft x-ray diagnostics, especially as a narrowband detector in the 100-eV photon energy range where peak measured efficiencies can exceed 300%.

Optimized multilayer X-ray spectrometry, using lead myristate and lead stearate analyzers (2d values of 80 and 100 A) has been applied to the measurement of the O--Kα and the C--Kα spectral bands from CO and CO2 in the gas and solid phases. The LII, III spectra were also measured for argon in the gas and solid states under similar conditions in order to identify and to minimize any non-molecular components in the CO and CO2 spectra. These molecular orbital data have been related to those obtained with X-ray and ultraviolet photoelectron spectroscopy and grating X-ray spectroscopy. The consistency of the results of these complementary measurements is excellent. The ionization energies for the C and O 1s levels have been determined to be 295.4 and 542.0 eV for CO and 296.8 and 540.3 eV for CO2. The MO data have also been compared with that predicted from the symmetry, strength and binding energy of the molecular orbital spectral components as calculated using the currently available computational models, CNDO/2, MINDO/3, MNDO, extended Huckel and ab initio. The molecular orbital calculated results for these organic compounds, CO and CO2, are not in as good agreement with the experimental data as previously demonstrated for molecular orbital spectra measured for C--Kα and the LII, III bands of Cl, S and P for both organic and inorganic compounds.

In this talk, measurements of thermal transport in spherical geometry using time-resolved x-ray spectroscopy are presented. The time dependence of the mass ablation rate (m) is determined by following the progress of the ablation surface through thin layers of material embedded at various depths below the surface of the target. These measurements made with 6, 12 and 24 uv (351 nm) beams from OMEGA are compared to previous thermal transport data and are in qualitative agreement with detailed LILAC hydrodynamic code simulations which predict a sharp decrease in m after the peak of the laser pulse. Viewgraphs of the talk comprise the report.

A new spectrographic system has been developed and calibrated in this laboratory for the absolute spectrometry of high‐intensity pulsed x‐ray sources in the 100–10 000‐eV region. This spectral region is analyzed with fixed elliptically curved crystals and molecular or sputtered‐or‐evaporated multilayers of 2d values in the 3–160‐A range. Twin channels are utilized for simultaneous time‐integrated photographic recording and for time‐resolved x‐ray streak camera recording. Absolute calibrations of the elliptical analyzers, of the photographic film, and of the gold and CsI transmission photocathodes have been made using monoenergetic, cw laboratory x‐ray sources. The overall transmission characteristics of the spectrograph have also been determined. The instrument has been designed for mounting through a pneumatically controlled high‐vacuum valve onto a 4‐in. port of a 1‐m‐diameter source chamber and includes an appendage, high‐vacuum, sputter‐ion prepumping station. The initial dynamic testing and application of this new spectrographic system has been on the University of Rochester’s LLE 24 laser beam OMEGA source facility.

The general characteristics are compared for the plane, convex, and concave fixed crystal analyzers which may be applied to the spectrometry of concentrated, intense plasma sources of x radiation involved, for example, in fusion energy and x‐ray laser research. The unique advantages of the elliptical analyzer for precise and absolute spectral measurements are noted and detailed descriptions of its geometrical and physical optics are presented. With a source point at one of the foci of the elliptical analyzer profile, the spectrum is Bragg reflected (45°

A low-energy spectrometer for the X-ray analysis of plutonium and plutonium-containing materials has been built. We use ultra-thin window to maintain different pressures and contamination level in the spectrometers's sample and crystal chambers. Ultra-thin windows are also used on the X-ray tube and detector. Methods have been developed by which the spectrometer can analyze both metal and loose-powder samples. Representative calibration spectra are presented for the fluorine band in polyfluoroethylene, the oxygen band in α-Al2 O3, and the carbon band in graphite. Experimental spectra are presented for the fluorine band in PuF3 and for the oxygen ban in PuO2.

We present results of a laser Doppler‐shift technique which gives the velocity profiles of ablatively accelerated targets. Measurements of the effects of laser beam nonuniformity on the target acceleration are presented and interpreted in the context of laser pellet fusion.

New developments in forming thin-film x-ray tube and detector windows and building large of d-spacing analyzing crystals have resulted in 30- to 50-fold increases in the counting rates for oxygen K alpha in silicates using a vacuum-path x-ray spectrometer. A test of the precision of oxygen determinations over the range 44 to 54% shows that it is now possible to achieve better than 1 percent relative standard deviation in routine rock analyses. This improved precision allows the detection of significant biases in calibration which seem to be caused by an inadequate knowledge of the concentrations of the other elements present and by the lack of adequate standards. /Author/

Investigations of the many transient features of the high density plasmas produced in laser fusion and x-ray laser studies have stimulated the development of many x-ray and XUV diagnostic techniques. We review here a broad range of x-ray diagnostic instrumentation to spatially, spectrally and temporarily resolve x-ray emission from plasmas of direct interest to laser fusion, high density atomic physics studies and x-ray laser investigations performed at the OMEGA irradiation facility over the past few years. Several categories of instruments are described, including time-resolving x-ray crystal and transmission grating spectrographs, soft and hard x-ray spectrometric systems, a streak x-ray photographic system, and approaches to fast-time framing x-ray photography, radiography and spectroscopy. The primary characteristics of each approach are described and illustrated with typical data drawn from experiments performed on the 24-beam IR (1054/nm) and UV (351 nm) OMEGA system.

Recent advances in the development of high resolution time-resolving x-ray spectroscopic instrumentation have considerably improved the capabilities of diagnosing details of electron and radiation transport, implosion dynamics and final compressed core conditions of laser fusion targets. In addition, the current interest in x-ray laser schemes utilizing laser-produced plasmas places even more stringent demands on time- and space-resolved x-ray and XUV diagnostics. In this paper we will summarize some of the recent technical developments made at LLE to meet these needs, and give illustrations of the capabilities of new x-ray spectroscopic instrumentation activated on recent laser fusion and x-ray laser experiments. Technical details, performance criteria and typical experimental results will be presented on several time resolving spectrographic systems. A soft x-ray, transmission grating, streak spectrograph (resolution ~ 1.5 A) time-resolves spectra in the 3-200 A range. A streak elliptical crystal spectrograph permits the resolution of x-rays in a number of spectral regions in the 2-100 A range. We will also present details of (a) a streak planar crystal spectrograph having high spectral resolution and sensitivity, and (b) a novel, high resolving power (λ/Δλ ~ 103) streak spectrograph incorporating a unique crystal geometry permitting high dispersion, and having good collection efficiency. The impact these developments will have on current investigations of high temperature, dense plasmas in laser fusion and x-ray laser research will be discussed.

The moleular and sputtered/evaporated multilayers and the acid phthalate crystals can be applied for relatively fast, high effiiency spectral analysis of constant and pulsed low energy x‐ray sources in the 100 to 2000 eV region. Limits of resolution are about 1 eV. Reviewed here are the basic methods for the theoretical and the experimental characterization of these analyzers as required for absolute x‐ray spectometry. The design and absolute calibration of spectrographs for pulsed low energy x‐ray source diagnostics are described.

In this paper we present measurements of thermal transport in spherical geometry made with 24 uv (351-nm) beams from the OMEGA laser system of the Laboratory for Laser Energetics of the University of Rochester. The measurements, using time-resolved x-ray spectroscopy on solid glass targets coated with varying thicknesses of plastic, provide absolute measurements of the onset times of the resonance x-ray lines of silicon. From these measurements, the scaling of the instantaneous mass-ablation rate with absorbed intensity is obtained for times before and after the peak of the laser pulse. The observed large burnthrough depths and early onsets of the x-ray lines are explained by carrying out detailed hydrodynamic-code simulations for the range of the estimated laser-intensity distribution on target which is obtained from the superposition of the equivalent target-plane intensity distribution of a single beam. We find that neglecting the effects of laser illumination nonuniformities can lead to erroneous conclusions about the heat transport. We conclude from the analysis that the experimental results can be explained by the presence of significant energy at intensities three times the nominal intensity, contained in hot spots of size less than 20 ..mu..m. This is almost twice as much as the maximum intensitymore » obtained from the superposition of the single-beam distribution.« less

X-ray crystal spectroscopy of laser produced plasmas has long been considered an important diagnostic of plasma density and temperature.(1) Absorption spectroscopy of the dense transient plasmas existing in imploding laser fusion targets has the potential of being an important avenue of fuel and shell density and temperature diagnosis.(2,3) Meaningful data, however, will require sufficient space and/or time resolution to pinpoint the region of the plasma being diagnosed. In this paper we review recent progress made in this area in studying spherical fusion targets imploded by the 24 beam OMEGA laser system at LLE.(4) Space resolved spectra have been obtained with a multi-frame imaging planar crystal i)ectrometer,(5) and time-resolved data with the SPEAXS curved crystal streak spectrograph.(6'7) The evolution of the intensity of the spectral features as a function of space for different types of targets has been investigated in order to make estimates of the density and temperature of the shell during the final stages of compression of the imploding fusion target. Comparisons of this technique with other diagnostic approaches are also made.

For the low energy x‐ray region of 100‐2000 eV, the complete atomic interaction, coherent scattering and photoelectric absorption can be desribed by a complex scattering amplitude which may be given through the atomic scattering factor, f1+if2. For this low photon energy region, it is shown by the relativistic quantum dispersion theory that the atomic scattering factors can be uniquely determined from simple relations involving only the atomic photoionization cross section dependence upon photon energy. We have compiled ‘‘state of the art’’ tables for the photoionization cross sections for 94 elements and for the photon energy region of 30−100,000 eV. With this compilation, we have established atomic scattering factor tables for the 100−2000 eV region. By a summing of the complex, atomic scattering amplitudes, a low energy x‐ray interaction can be determined. Even for atoms in the molecular or solid state the scattering cross sections remain atomic‐like except for photon energies very near the thresholds. Using practival examples, the methods of calculation, with the atomic scattering factors, are reviewed here for the followig: 1) x‐ray energy deposition within materials (energy response of x‐ray photocathodes); 2) transmission through a homogeneous medium: refraction; 3) transmission through a random collection of uniform spheres: low angle scattering in an inhomogeneous medium; 4) specular, Fresnel reflection (total and large angle reflection) at smooth boundry; and 5) Bragg reflection from a periodic, layered system‐(reflection by crystals and multilayers).

Our low energy x-ray photoabsorption and scattering factor tables along with methods for their application were published in 1982 (1). The photoabsorption cross sections were compiled for the 30-10,000 eV region, with which, using the Kramers-Kronig dispersion integrals, the zero-angle atomic scattering factors were determined for the 100-2000 eV region. These tables are now being revised, based upon the 1987 experimental photoabsorption data base as extended down to 10 eV and with the calculated zero-angle atomic scattering factors for the extended 50-10,000 eV region. Refined methods of application of these tables to modern problems of x-ray spectrometry design involving filters, mirrors and crystal-multilayer analyzers will be included in this revision.

Transport of energy in laser‐produced plasmas is scrutinized by devising spectrally and temporally identifiable characteristics in the x‐ray emission history which identify the heat‐front position at various times in the heating process. Measurements of the relative turn‐on times of these characteristics show the rate of energy transport between various points. These measurements can in turn constrain models of energy transport phenomena. We are time‐resolving spectrally distinguishable subkilovolt x‐ray emissions from different layers of a disk target to examine the transport rate of energy into the target. A similar technique is used to measure the lateral expansion rate of the plasma spot. A soft x‐ray streak camera with 15‐psec temporal resolution is used to make the temporal measurements. Spectral discrimination of the incident signal is provided by multilayer x‐ray interference mirrors. These synthetic x‐ray crystals have been characterized for reflectivity and bandwidth and exhibit resolutions E/ΔE of 10 to 90.

A procedure is described for the detailed characterization of multilayer analyzers which can be effectively applied to their design, optimization and application for absolute x-ray spectrometry. An accurate analytical model has been developed that is based upon a simple modification of the dynamical Darwin-Prins theory to extend its application to finite multilayer systems. Its equivalence to the optical E&M solution of the Fresnel equations at each interface is demonstrated by detailed calculation comparisons for the reflectivity of a multilayer throughout the angular range of incidence of 0 to 90° . A special spectrograph and experimental method is described for the measurement of the absolute reflectivity characteristics of the multilayer. The experimental measurements at three photon energies in the 100-2000 eV region are fit by the analytical modified Darwin-Prins equation (MDP) for I( 0), generating a detailed characterization of two "state of the art" multilayers, a sputtered tungsten-carbon of 2d 21 70 A and a molecular lead stearate of 2d 100 A. The fitting parameters that are determined in this procedure are applied to help establish the structural characteristics of the particular multilayer.

We present details of an absolutely calibrated twin channel x-ray spectrometer employing elliptically curved x-ray analyzer crystals. The spectrometer utilizes high-energy cut-off grazing incidence mirrors, low-energy cut-off K-edge filters and a stable of analyzer crystals including naturally occurring crystals and molecular multilayers, allowing coverage of the spectral region from 100 to 10,000 eV with a resolution of - 3 eV. One channel of the spectrometer is recorded on photographic film; the second is coupled to an x-ray streak camera of novel design which incorporates a large aperture (40 mm) photo-cathode and has a time resolution of less than 10 ps. All of the components of the spectrometer have been absolutely calibrated using a monochromatic D.C. x-ray source and proportional counter system. By cross-calibrating the time-resolving channel with the time integrating channel we obtain absolutely calibrated time-resolved spectra. This instrument has been used extensively to diagnose laser-produced plasmas at the University of Rochester's Laboratory for Laser Energetics. In this paper we will present some typical time-resolved spectra to illustrate the capabilities of the spectrometer, its sensitivity and wide application. In addition, we discuss the performance characteristics of the x-ray streak camera design.

A procedure is described for a detailed characterization of multilayer analyzers that can be effectively applied to their design, optimization, and application for absolute x-ray spectrometry in the 100 to 10,000 eV photon energy region. An accurate analytical model has been developed that is based upon a simple modification of the dynamical Darwin-Prins theory to extend its application to finite multilayer systems and to the low energy x-ray region. Its equivalence to the optical E&M solution of the Fresnel equations at each interface is demonstrated by detailed comparisons for the reflectivity of a multilayer throughout the angular range of incidence of 0° to 90°. A special spectrograph and an experimental method are described for the measurement of the absolute reflectivity characteristics of the multilayer. The experimental measurements at three photon energies in the 100 to 2000 eV region are fit by the analytical modified Darwin-Prins equation (MDP) for 1(0), generating a detailed characterization of two state-of-the-art multilayers: sputtered tungsten-carbon with 2d 70 A and a molecular lead stearate with 2d 100 A. The fitting parameters that are determined by this procedure are applied to help establish the structural characteristics of these multilayers.

The spectral and temporal nature of the soft x-ray emission from high-Z spherical targets uniformly irradiated with 351 nm laser light has been characterized, and compared to one-dimensional LASNEX calculations.

The soft x-ray contact microscopy station at LBL images wet, living biological specimens with a resolution better than 1000 A. High doses of soft x-rays are required to record a latent image onto a polymer resist which is then developed and examined by electron microscopy. In order to interpret the resulting image, it is necessary to determine whether the structure of the cell has changed during the exposure. We would therefore like to know which components of the cell change, how much radiation is necessary to produce the change, and whether the structural changes affect the soft x-ray micrograph. Before these questions may be answered, we must establish a dosimetric standard for soft x-ray microscopy. The soft x-ray contact microscopy station was calibrated by using radiachromic nylon film which in turn was standardized with a known source at our laboratory.

This report describes a synthesis of more than 10 years of this program's development and application of multilayer analyzers for absolute Bragg spectrometry in the low-energy x-ray region of 50-1000 eV. Multilayers, denned here as systems of periodic layered structures parallel to the analyzer surface, have been applied principally in the diagnostics and application of the new, intense sources of synchrotron and high-temperature plasma x radiation. Detailed absolute reflectivity characterizations are presented for selected examples of these multilayers which have been semiempirically determined for mica, potassium acid phthalate, and the fabricated Langmuir-Blodgett and sputtered multilayer analyzers with d-spacings in the 10-200 Å range. Design requirements for absolute spectrometry are established. Efficient analytical multilayer reflectivity models are derived and parameterized (based upon a modification of the Darwin-Prins model for the low-energy x-ray region), including, for the sputtered multilayers, parameters for defining interface structure. The dependence of the reflectivity characteristics, high-order Bragg diffraction suppression, and overall efficiency upon the model parameters is analyzed. A special spectrograph and procedure for the absolute measurement of the relevant reflectivity characteristics are described. Detailed measurements and semiempirical characterizations are presented. Programs for small laboratory computers have been developed that allow rapid and flexible spectral analysis, transforming measured spectra to absolute Spectra.

Recent developments in high resolution x‐ray measurements are reviewed. Among the more interesting developments are sub‐1000A x‐ray images, multilayer x‐ray interfernce coatings, free standing transmission gratings, 20 psec soft x‐ray streak cameras, normal incidence x‐ray mirrors, and tabulated atomic scattering factors.

In this report we will review recent developments in our x -ray streak camera program. The characterization of thelinearity and dynamic range of these diagnostics is vital for quantitative analysis of the data, which can then be compared tohydrocode simulations. Examples of time -resolved x -ray imaging and x -ray spectroscopy are presented to illustrate our currentcapabilities. Introduction Time -resolving x -ray instrumentation provides an important research tool for studying laser fusion plasmas. These instruments use the ten -picosecond time resolution capabilities of x -ray streak cameras to record the output of an x -ray spectrometer or imaging device. Generally, several x -ray streak cameras are deployed simultaneously on a given experimentto provide a comprehensive data set of the x -ray emission spectrum and target hydrodynamics. Careful synchronization of thevarious streak records to each other and to the incident laser pulse through the use of optical timing fiducials allows us to

Optical density versus exposure data have been obtained at nine photon energies in the 100–2000-eV x-ray region for five spectroscopic films (Kodak films 101-07, SB-392, RAR 2492, RAR 2495, and RAR 2497). These data were determined operationally by a direct comparison of the peak absolute intensities of spectral lines, which were measured with a calibrated proportional counter, with the microdensitometer tracings of the corresponding photographically recorded spectral lines. Film-resolution limits were deduced from an analysis of contact microradiograms of linear zone plates constructed of gold bars. The relationship between the specular densities as measured here and the diffuse densities have been experimentally determined for the five films. Finally, experimental measurements of the optical density versus the angle of incidence of exposing radiation of constant intensity were obtained. These data, relating density to the x-ray intensity, its photon energy, and its angle of incidence, are shown to be fitted satisfactorily in the 100–10 000-eV region by the semiempirical mathematical model relations that were derived in Part I of this research [ J. Opt. Soc. Am. B1, 818– 827 ( 1984)].

A detailed characterization has been established for the new, high-sensitivity double-emulsion Kodak Direct Exposure Film (DEF). The experimental data base consisted of density-versus-exposure measurements that were duplicated at several laboratories for x radiations in the 1000–10,000-eV region. The absorption and geometric properties of the film were determined, which, along with the density-exposure data, permitted the application of a relatively simple analytical model description for the optical density, D, as a function of the intensity, I (photons/μm2), the photon energy, E (eV), and the angle of incidence, θ, of the exposing radiation. A detailed table is presented for the I values corresponding to optical densities in the 0.2–2.0 range and to photon energies, E (eV), in the 1000–10,000-eV region. Experimentally derived conversion relations have been obtained that allow the density values to be expressed as either diffuse or specular. Also presented here is a similar characterization of the complementary, single-emulsion x-ray film, Kodak SB-5 (or 392). For the 1000–10,000-eV region this x-ray film is appreciably less sensitive but has higher resolution.

Relatively simple mathematical models are developed to determine the optical density as a function of the x-ray intensity, its angle of incidence, and its photon energy in the 100–10,000-eV region for monolayer and emulsion types of photographic films. Semiempirical relations are applied to characterize a monolayer film (Kodak 101-07) and an emulsion-type film (Kodak RAR 2497); these relations fit calibration data at nine photon energies well within typical experimental error.

The use of silver halide x‐ray films for imaging and spectroscopy is limited by the range of intensities that can be recorded and densitometered. Using the manufacturers processing techniques can result in 102–3 range in intensity recorded over a 0–5.0 density range. By modifying the chemistry and processing times, ranges of 105–6 can be recorded in the same density range. We report on x‐ray film calibration work and dynamic range improvements. Changes to the processing chemistry and the resulting changes in dynamic range and x‐ray sensitivity will be discussed. Work performed under the auspices of the U. S. DOE by Lawrence Livermore National Laboratory under Contract No. W‐7405‐ENG‐48.