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This research utilizes a valuable data source to explain voter registration and political knowledge by Native Americans, testing theories of the political engagement of minority populations. After taking account of socio-economic resources, American Indians exhibit lower rates of voter registration and political knowledge compared to Caucasians but similar to that of Hispanics. Relative to other racial groups, military service greatly enhances American Indian political knowledge and voter registration. This finding is especially noteworthy given American Indians' high rate of military service.

Objective Compare the impact of being a racial minority for influencing political trust as measured by the standard, NES‐developed measures with its impact on assessments of the capacity of decisionmakers to make racially unbiased spending and hiring decisions. Additionally, to examine the political trust of American Indians, an understudied racial minority. Methods Bivariate and multivariate analysis of 2004 and 2008 National Annenberg Election Study survey data. Results Self‐designation as a racial minority exercises small, inconsistent effects on the standard measures of political trust and external efficacy. When citizens are asked whether Caucasian government officials make decisions on spending and hiring to advantage whites to the disadvantage of blacks and Hispanics, racial minorities state that they expect racial bias. American Indians reveal levels of political trust similar to those held by other racial minorities. Conclusion An increasingly multiracial society will experience considerable tensions as minorities distrust government decisionmakers of a different race. These tensions will continue to be exploited by ambitious political elites.

This research examines the partisan inclinations of American Indians, a minority population with a complicated history with the U.S. government and American society. The empirical analyses identify Native Americans as preferring the Democratic Party over the Republican Party. The impact of being Native American on identification with the Democratic Party is sizable, equivalent to the effect for being Hispanic, Asian, or female. In addition, American Indians demonstrate a pronounced tendency to not affiliate with a major American political party. The higher incidence of non-identification among Native Americans likely results from the importance of their claims for sovereignty and, relatedly, living separate from much of American society. Unlike other broad-based social groups in American politics, Native Americans disseminate cues that reduce the tendency of their members to affiliate with a major political party.

Gated X-ray framing cameras are used to measure important characteristics of inertial confinement fusion (ICF) implosions such as size and symmetry, with ~50 ps time resolution in two dimensions. A pulsed source of hard (>8 keV) X-rays, would be a valuable calibration device, for example for gain-droop measurements of the variation in sensitivity of the gated strips. We have explored the requirements for such a source and a variety of options that could meet these requirements. We find that a small-size dense plasma focus machine could be a practical single-shot X-ray source for this application if timing uncertainties can be overcome.

One expectation for American election campaigns is that they inform citizens about candidates' policy inclinations, clarifying the policy directions advocated by the major party nominees. Evidence from the 1998 elections to the House of Representatives indicates that the more negative issue advertisements were broadcast, the more confident citizens became that they knew the targeted candidate's ideological position. However, the more negative issue advertisements about a candidate aired, the greater citizens' perceptual error of the candidate's ideological position. Issue attack ads lead citizens to believe they know more than they actually do, failing to produce the democratic ideal of an informed electorate.

In inertial confinement fusion experiments, implosion of a cryogenic hydrogen isotope-filled capsule produces a plasma with a high-temperature, low-density core (the hot spot) surrounded by a low-temperature, high-density main fuel layer. Experimental measurements of temperature and density profiles in the hot spot are critical for implosion diagnosis. In this paper, we propose a simple technique for measuring core temperature and density profiles in cryogenic implosion plasmas. This technique uses absolutely calibrated continuum emission spectroscopy coupled with two-dimensional imaging to allow temperature and density profiles to be measured directly. We develop the technique analytically, and validate it using synthetic data and hydrodynamics simulation results. We find that the technique should be sufficiently accurate to measure central temperatures and densities to better than 20%. The technique may also find application to the diagnosis of other types of plasmas.

An intense laser impinging upon dense matter converts a large fraction of its energy into fast electrons. (Here we take “fast” to mean electrons that are much more energetic than the normal Boltzmann-like distribution measured in the tens to hundreds of eV.) Upon transiting the interior of the dense matter, these electrons are responsible for isochoric heating of the material. Just how these electrons traverse the material, and various interfaces within the material, is a subject of substantial amounts of computation and theory, and recently, experiments. Here we outline the nature of the heating mechanisms, and the current level of understanding of the complex physical processes. In particular we discuss new experimental techniques to record essential features of this transport problem.

The use of high-intensity lasers to cause ignition in inertial confinement fusion is presented, with emphasis on current experimental programs and physical concepts that are at the forefront of the field. In particular, we highlight the issues of fast electron transport through dense materials, an essential element of the “Fast Ignitor” concept.

Recent scholarship on American voting behavior contends that political cynicism prompts citizens to support a third party candidate. I maintain this research fails to consider an alternative direction of causality between political trust and third party support. Using an exogenous measure of political trust, one uncontaminated by candidate preference, analysis demonstrates that political cynicism is shaped by preference for an American third party rather than being causally prior to that preference. Students of American electoral behavior must consider the possibility that major third party candidacies shape supporters’ political orientations and concerns in much the same manner as the major political parties do.

Targets for future laser-fusion ignition experiments will consist of a frozen deuterium-tritium ice layer adhering to the inner surface of a spherical shell, and the specifications for the inner surface quality of this ice layer are extremely demanding. We have developed a numerical raytrace model in order to validate backlit optical shadowgraphy as an ice-surface diagnostic, and we have used the code to simulate shadowgraph data obtained from mathematical ice layers having known modal imperfections. We find that backlit optical shadowgraphy is a valid diagnostic of the mode spectrum of ice-surface imperfections for mode numbers as high as 80 provided the experimental data are analyzed appropriately. We also describe alternative measurement techniques, which may be more sensitive than conventional backlit shadowgraphy.

Two-dimensional space-resolved temperature and density images of an inertial confinement fusion (ICF) implosion core have been diagnosed for the first time. Argon-doped, direct-drive ICF experiments were performed at the Omega Laser Facility and a collection of two-dimensional space-resolved spectra were obtained from an array of gated, spectrally resolved pinhole images recorded by a multi-monochromatic x-ray imager. Detailed spectral analysis revealed asymmetries of the core not just in shape and size but in the temperature and density spatial distributions, thus characterizing the core with an unprecedented level of detail., Published online 7 May 2014

When candidates assume issue positions opposite those of their sponsoring political party do citizens recognize these positions? Relatedly, what role do candidates' actual issue positions play in citizens' perceptions of their issue positions? Examining citizens' perceptions of 1996 and 1998 House candidates' position on abortion, this research finds that citizens' perceptions are shaped largely by partisan and, to a lesser extent, gender stereotypes. However, candidates' individuating positions on abortion influence perceptions of the candidates' position, but the effects are considerably stronger for perceptions of Republican candidates. Democratic candidates are likely to adopt anti-abortion positions in districts characterized by lower than average levels of political awareness and education, reducing the likelihood their party-contradicting position is accurately perceived. In contrast, Republican candidates adopt a pro-choice position in districts characterized by high education and political awareness, increasing the likelihood their position is accurately perceived.

This research tests whether the effects of assessments of presidential performance on the senate voting decision are largest for out-party incumbents and smaller for out-party incumbents and candidates in open-seat contests, a pattern suggested by the restricted in-party culpability thesis. Analysis of data from the 1988–1990–1992 Pooled Senate Election Study reveals that the effects of appraisals of presidential performance are greatest in open-seat contests and those with in-party incumbents, contrary to the restricted in-party culpability thesis. For incumbents of the out-party and candidates in open-seat contests, the effects of assessments of presidential performance are principally a function of the competitiveness of the contest. Assessments of presidential performance shape the voting decision in contests with in-party incumbents regardless of the level of electoral competitiveness.

We have developed a hybrid Ti:sapphire-Nd:glass laser system that produces more than 1.5 PW of peak power. The system has produced up to 680 J of energy on target at 1054 nm in a compressed 440/spl plusmn/20-fs pulse by use of 94-cm diffraction gratings. A focused irradiance of up to 6/spl times/10/sup 20/ W/cm/sup 2/ was achieved using an on-axis parabolic mirror and adaptive optic wavefront control. Experiments with the petawatt laser system focused the beam on solid targets and produced a strongly relativistic interaction. Energy content, spectra, and angular pattern of the photon, electron, and ion radiations were diagnosed in a number of ways, including several nuclear activation techniques. Approximately 40-50% of the laser energy was converted to broadly beamed hot electrons, with an associated bremsstrahlung beam. High luminosity ion beams were observed normal to the rear surface of various targets with energies up to /spl ges/55 MeV, representing /spl sim/7% of the laser energy. These and other results are presented.

In recent Petawatt laser experiments at Lawrence Livermore National Laboratory, several hundred joules of 1 μm laser light in 0.5–5.0-ps pulses with intensities up to 3×1020 W cm−2 were incident on solid targets and produced a strongly relativistic interaction. The energy content, spectra, and angular patterns of the photon, electron, and ion radiations have all been diagnosed in a number of ways, including several novel (to laser physics) nuclear activation techniques. About 40%–50% of the laser energy is converted to broadly beamed hot electrons. Their beam centroid direction varies from shot to shot, but the resulting bremsstrahlung beam has a consistent width. Extraordinarily luminous ion beams (primarily protons) almost precisely normal to the rear of various targets are seen—up to 3×1013 protons with kTion∼several MeV representing ∼6% of the laser energy. Ion energies up to at least 55 MeV are observed. The ions appear to originate from the rear target surfaces. The edge of the ion beam is very shar...

This research examines whether citizens utilize gender stereotypes to infer candidates' ideological orientations. Analysis of data from the 1988-1990-1992 Pooled Senate Election Study reveals that even after candidates' individuating ideological orientations are taken into account, candidate gender still exerts substantial effects on citizens' perceptions of candidates' ideological orientations. The consequences of gender stereotypes for vote choice are important but differ for Democrats and Republicans. For Democratic female candidates, gender ideological stereotypes increase the distance between female candidates and voters, increasing the likelihood citizens will vote for the Republican opponent, ceteris paribus. For Republican female candidates, gender stereotypes for ideology reduce the distance between them and most voters, thereby increasing their electoral prospects.

Many of the conditions believed to underlie astrophysical phenomena have been difficult to achieve in a laboratory setting. For example, models of supernova remnant evolution rely on a detailed understanding of the propagation of shock waves with gigabar pressures at temperatures of 1 keV or more, at which radiative effects can be important. Current models of gamma-ray bursts posit a relativistically expanding plasma fireball with copious production of electron-positron pairs, a difficult scenario to verify experimentally. However, a new class of lasers, such as the Petawatt Laser, is capable of producing focused intensities greater than 1020 W cm-2, at which such relativistic effects can be observed and even dominate the laser-target interaction. We report here on the development of a testbed using the Petawatt Laser to study the evolution of strong, radiative shock waves. There is ample evidence in observational data from supernova remnants of the aftermath of the passage of radiative shock or blast waves. In the early phases of supernova remnant evolution, the radially expanding shock wave expands nearly adiabatically since it is traveling at a very high velocity as it begins to sweep up the surrounding interstellar gas. A Sedov-Taylor blast wave solution can be applied to this phase when the mass of interstellar gas swept up by the blast greatly exceeds the mass of the stellar ejecta, or a self-similar driven wave model can be applied if the ejecta play a significant role. As the mass of the swept-up material begins to greatly exceed the mass of the stellar ejecta, the evolution transitions to a radiative phase wherein the remnant can be modeled as an interior region of low-density, high-pressure gas surrounded by a thin, spherical shell of cooled, dense gas with a radiative shock as its outer boundary, the pressure-driven snowplow. Until recently it has not been feasible to devise laboratory experiments wherein shock waves with initial pressures in excess of several hundred megabars and temperatures approaching 1 keV are achieved in order to validate the models of the expanding blast wave launched by a supernova in both of its phases of evolution. This new experiment was designed to follow the propagation of a strong blast wave launched by the interaction of an intense short-pulse laser with a solid target. This blast wave is generated by the irradiation of the front surface of a layered, solid target with ~400 J of 1 μm laser radiation in a 20 ps pulse focused to a ~50 μm diameter spot, which produces an intensity in excess of 1018 W cm-2. These conditions approximate a point explosion, and a blast wave that has an initial pressure of several hundred megabars and that decays as it travels approximately radially outward from the interaction region is predicted to be generated. We have utilized streaked optical pyrometry of the blast front to determine its time of arrival at the rear surface of the target. Applications of a self-similar Taylor-Sedov blast wave solution allows the amount of energy deposited to be estimated. By varying the parameters of the laser pulse that impinges on the target, pressures on the order of 1 Gbar with initial temperatures in excess of 1 keV are achievable. At these temperatures and densities radiative processes are coupled to the hydrodynamic evolution of the system. Short-pulse lasers produce a unique environment for the study of coupled radiation hydrodynamics in a laboratory setting.

Prior studies of third-party movements document both an individual- and aggregate-level relationship between disatisfaction with government and its leaders and third party support. Unfortunately, these studies are unable to determine whether citizen dissatisfaction precedes third-party support or if third-party support results in heightened negativity toward the political system. Using American National Election Study data to ex amine 1992 Perot voters, I demonstrate that the causal direction is from third-party support to decreased trust in government and external effi cacy. Additionally, this research reveals that the Perot campaign increased voter turnout in 1992 by enhancing citizens' interest in that year's cam paigns and strengthening the relationship between interest in campaigns and voter turnout. These findings indicate that American third party movements can perform the mobilizing and mentoring functions com monly associated with the major parties.

Scholarship on congressional elections holds that competitive elections are different from noncompetitive elections. Specifically, some scholars argue that the level of competitiveness determines the criteria or the weight of various criteria for the voting decision. Using the 1988–1990–1992 Pooled Senate Election Study, this research finds that enhanced electoral competitiveness increases the importance of assessments of presidential performance on the voting decision. These effects are particularly large for voters with high levels of educational attainment. Contrary to previous research, in highly competitive elections the role of ideological considerations is smaller than in less competitive elections.

In previous research scholars consistently have documented that women in the United States are less psychologically engaged in the political process than men. Utilizing the unique electoral circumstances surrounding the 1990 and 1992 Senate elections, I determine if the presence of female candidates increases the psychological engagement of women in the electoral process. The empirical analyses suggest that the presence of female candidates by itself does not serve to increase women's engagement in the electoral process. Instead, the combination of issues involving women's representation in politics and female candidates serves to heighten women's psychological engagement in the electoral process. The importance of these results for a symbolic theory of representation and women's engagement in politics is discussed.

X-ray backlit radiographs of dense plasma shells can be significantly altered by refraction of x rays that would otherwise travel straight-ray paths, and this effect can be a powerful tool for diagnosing the spatial structure of the plasma being radiographed. We explore the conditions under which refraction effects may be observed, and we use analytical and numerical approaches to quantify these effects for one-dimensional radial opacity and density profiles characteristic of inertial-confinement fusion (ICF) implosions. We also show how analytical and numerical approaches allow approximate radial plasma opacity and density profiles to be inferred from point-projection refraction-enhanced radiography data. This imaging technique can provide unique data on electron density profiles in ICF plasmas that cannot be obtained using other techniques, and the uniform illumination provided by point-like x-ray backlighters eliminates a significant source of uncertainty in inferences of plasma opacity profiles from area-backlit pinhole imaging data when the backlight spatial profile cannot be independently characterized. The technique is particularly suited to in-flight radiography of imploding low-opacity shells surrounding hydrogen ice, because refraction is sensitive to the electron density of the hydrogen plasma even when it is invisible to absorption radiography. It may also provide an alternative approach to timing shockwaves created by the implosion drive, that are currently invisible to absorption radiography.

Images with 14 MeV neutrons of inertial confinement fusion (ICF) D,T fusion show the regions of most intense fusion burn, while images based on lower-energy “downscattered” neutrons can reveal regions of nonburning D,T fuel. The downscattered images can help to understand ICF implosion dynamics. Recording downscattered images is difficult because the images are relatively weak, and because they may be obscured by residual “afterglow” of more intense 14 MeV images. The effect of afterglow can be estimated by adding a sequence of images for neutron energies from 14 MeV down to the downscatteed energy of interest. The images will be subject to decay factors which depend on the time response of the neutron scintillator. Preliminary analyses suggest that afterglow will not prevent the recording of useful downscattered images.

In this paper we present time-resolved temperature measurements of a radiatively heated, thin tamped foil via Kα absorption spectroscopy. The sample foil was 1500 A MgO, tamped on both sides with 1000 A paralyene, and was heated by soft x-rays transmitted through the back side of a separate laser-irradiated 1500 A Au foil. The resulting plasma was then backlit by a separate laser-irradiated front-surface U foil, providing a time-resolved K -shell absorption spectrum over the duration of the heating phase. We compare the resulting data to synthetic spectra obtained from detailed simulations of the heating and expansion of the tamped foils, and find poor agreement. Much better agreement is obtained when we determine the temperatures through best-fit absorption spectra which assume temperatures ∗> 35% higher than predicted; the reason for this discrepancy is not yet understood.

This paper describes recent x-ray laser spectral linewidth measurements and discusses the consequences of these measurements. The experiments observed the 206.38- and 182.45-A laser transitions in neonlike selenium using an extremely high-resolution soft-x-ray spectrometer, and measured the spectral linewidths and relative spectral intensities of the laser lines from amplifiers of varying lengths. The data allow the intrinsic (unamplified) linewidths of the 206- and 182-A lasers to be extrapolated as 50 and 35 mA, respectively. The intrinsic spectral width of the 206-A laser is somewhat greater than the predicted 43-mA Voigt-profile width based on calculated transition rates and on the expected ion temperature in the plasma, and while the number of data points obtained with the 182-A laser is small and a conclusive comparison with calculations is not possible, the extrapolated intrinsic linewidth of this laser is clearly consistent with the predicted 37-mA Voigt-profile width and is not significantly broader or narrower than expected. The data also show significant gain narrowing of both lines with increasing amplifier length and show no significant rebroadening of the 206-A laser in long, saturated amplifiers. We discuss line broadening and line transfer calculations we have performed which show that the saturated 206-A laser line transfermore » behavior can be treated homogeneously due to non-negligible homogeneous lifetime broadening contributions, which significantly reduce inhomogeneous Doppler saturation rebroadening, and due to collisional redistribution rates which are large enough in any case to homogenize the otherwise inhomogeneous Doppler contributions. We also discuss the implications of these results with regard to earlier suggestions that Dicke narrowing effects could play a significant role in determining the intrinsic line profiles of these laser transitions, and we conclude that Dicke narrowing effects are not likely to be significant for either laser.« less

We point out that existing Ne-like X-ray lasers have sufficient brightness to be used as pump sources in resonant pump-fluorescence experiments, and we discuss some of the potential benefits and limitations of such experiments. In preliminary experiments, we have measured the line overlap of the Ne-like yttrium X-ray laser near 155 A with 4f−3d transitions in H-like Na and He-like Mg. These experiments used a high-resolution grating spectrometer, and calibrated the wavelength of the yttrium laser by comparison against lines of known wavelength. The results indicate that the wavelength of the yttrium laser is 154.985 ± 0.025 A, a factor of 2–4 improvement in precision over previous calibrations. We find that the yttrium laser is ≈ 100 mA to the long-wavelength side of both the He-like Mg line and the H-like Na line, so that neither resonance is perfect; however, Stark broadening could improve the overlap in the latter scheme, and bulk Doppler shifting could improve both resonances. We also find a good resonance between the yttrium laser and an un-identified transition which we tentatively attribute to copper.

This research examines the relationship between citizens' assessments of how much influence the group they identify with is able to exercise in American politics and their subjective political competence and political participation. Appraisals of group influence have a powerful effect on subjective political competence, fulfilling theoretical expectations outlined by Leon Festinger many years ago. Moreover, assessments of group influence affect individuals' decision concerning membership in an interest group that promotes the interest of one's reference group. The work reported here is an improvement over past efforts in that it explicitly defines and assesses the causal importance of a concept that has been featured in prior research.

We report the first observation of hyperfine splitting on an x-ray laser transition. Hyperfine splitting can have a major impact on laser gain and help explain anomalous behavior and poor performance of x-ray lasers with odd [ital Z]. In our experiments we measure the line shape of the [ital J]=0[r arrow]1, 3[ital p][r arrow]3[ital s] transition in Ne-like Nb and Zr and observe a 28 mA splitting between the two largest hyperfine components in the Nb ([ital Z]=41) line at 145.9 A, in good agreement with theory. As predicted, no splitting is observed in Zr ([ital Z]=40).

The purpose of this research is to examine the theoretical considerations and empirical evidence for the operationalization of an important concept. I attempt to determine if group membership is a necessary condition for group identification and discuss the role of group identifications for translating political interests into political preferences.

A novel and simple soft-x-ray grating-spectrograph design for high-resolution plasma-spectroscopy applications is presented and analyzed. This design uses dual, matched, concave varied-groove-density gratings to provide high dispersion and slit magnification and can achieve a very high spectral resolution (λ/Δλ > 25,000) in an instrument that is less than 1 m in length while using detectors, such as microchannel plates, with relatively coarse spatial resolutions. The advantages of this design over other designs with a comparable spectral resolution include its simplicity and small size, whereas the disadvantages include a narrow useful spectral range (λ/Δλ ≈ 50). Potential applications include x-ray laser linewidth measurements.

We report on the first successful measurements of the spectral width of an x-ray laser line. The experiments observed the 206.38-\AA{} laser in Ne-like Se and indicate an unamplified width of 50 m\AA{}, show gain narrowing to 10 m\AA{} in intermediate length amplifiers, and show no significant rebroadening in saturated amplifiers. The unamplified width is 1.4 times the expected Doppler width, and the lack of rebroadening leads to speculation that collisional effects may play a significant role in determining the line profiles.

Laboratory x‐ray lasers are currently being studied by researchers worldwide. This paper reviews some of the recent work carried out at Lawrence Livermore National Laboratory. Laser action has been demonstrated at wavelengths as short as 35.6 A while saturation of the small signal gain has been observed with longer wavelength schemes. Some of the most successful schemes to date have been collisionally pumped x‐ray lasers that use the thermal electron distribution within a laser‐produced plasma to excite electrons from closed shells in neon‐ and nickel‐like ions to metastable levels in the next shell. Attempts to quantify and improve the longitudinal and transverse coherence of collisionally pumped x‐ray lasers are motivated by the desire to produce sources for specific applications. Toward this goal there is a large effort underway to enhance the power output of the Ni‐like Ta x‐ray laser at 44.83 A as a source for x‐ray imaging of live cells. Improving the efficiency of x‐ray lasers in order to produce saturated output with smaller pump lasers is also a goal of this work.

We report on measurements of the output power from the J = 2–1 (λ = 15.5 nm) neonlike yttrium soft-x-ray laser. The results show peak powers of 32 MW in an output pulse width of 200 ps (FWHM) and an integrated energy of 7 mJ. The output is consistent with the expected saturation intensity of this laser and makes this system one of the brightest XUV sources available.

High-brightness and short-pulse-width ( approximately 200 ps) x-ray lasers offer biologists the possibility of high-resolution three-dimensional imaging of specimens in an aqueous environment without the blurring effects associated with natural motions. As a first step toward developing the capabilities of this type of x-ray microscopy we have used a tantalum x-ray laser (lambda = 4.483 nm) together with an x-ray zone plate lens to image a test pattern. The observed image shows a detector-limited resolution of approximately 75 nm and paves the way to three dimensional biological imaging with high spatial resolution (20-30 nm).

Previous studies of group economic voting have not examined how citizens explain group economic problems and how those causal explanations might affect the role of group economic conditions and the consequent formation of citizens' political preferences. This research addresses three questions: (a) How do citizens explain group economic predicaments? (b) Are there meaningful, systematic variations in the explanations offered by citizens for both individual and group economic problems that coincide with our understanding of differing group schemas, societal values, and economic predicaments? (c) Do citizens' explanations of group problems determine the effect that assessments of group economic predicaments have on political preferences? The research presented here indicates citizens are more likely to cite political or social factors to explain group economic problems. Members of disadvantaged groups are more likely to cite political explanations. Assessments of group economic well-being that are explained by reference to political factors have a larger effect on political preferences than those explained by social factors.

We performed a direct side-by-side comparison of a Shack-Hartmann wave-front sensor and a phase-shifting interferometer for the purpose of characterizing large optics. An expansion telescope of our own design allowed us to measure the surface figure of a 400-mm-square mirror with both instruments simultaneously. The Shack-Hartmann sensor produced data that closely matched the interferometer data over spatial scales appropriate for the lenslet spacing, and much of the

We present recent results using multi-monochromatic X-ray imaging of direct drive implosions at the OMEGA laser facility. An array of pinholes coupled to a flat multilayer mirror provides multispectral images distributed over a wide spectral range. Using Argon as a dopant in the DD-filled plastic shells produces emission images in the Ar He-β and Ly-β spectral regions. When used in conjunction with gated imaging detectors the instrument provides images with spatial resolution of ∼10μm and temporal resolution of ∼50ps. A special algorithm has been developed to reconstruct narrow-band images, which will allow the retrieval of temperature, and density maps of the core as it evolves through peak compression.

We are studying the feasibility of utilizing K D x-ray sources in the range of 20 to 100 keV as a backlighters for imagingvarious stages of implosions and high aerial density pl anar samples driven by the NIF laser facility. The hard x-ray K Dsources are created by relativistic electron plasm a interactions in the targ et material after a radiation by short pulse highintensity lasers. In order to understand KD source characteristics such as production efficiency and brightness as a function of laser parameters, we have performed ex periments using the 10 J, 100 fs JanUSP laser. We utilized single-photon counting spectroscopy and x-ray imaging diagnostics to characterize the KD source. We find that the KDconversion efficiency from the laser energy at 22 keV is ~3 x 10 -4 .Keywords: Short pulse laser, K D source, backlighter INTRODUCTION X-ray radiography using back lighter sources has been an important tool for diagnosing and imaging various stages oflaser induced implosion. Until now, implosion experiments at Omega utilize

Neon-like niobium X-ray lasers have been studied using both slab and thin-foil target geometries. Niobium foils of various lengths were irradiated from both sides with two beams of the frequency-doubled Nova laser system using a line focus. We looked for gain by measuring spectrally integrated line intensities at different plasma lengths. Gain was observed in four neon-like niobium lines corresponding to 3s−3p transitions. The line profile of theJ = 0−1 line (λ = 145.9 A) shows splitting due to the hyperfine effect. Improved contrast in the hyperfine structure is observed as the plasma length is increased. Hyperfine splitting may be relevant to other 3s−3p transitions in neon-like niobium as well as other neon-like X-ray laser systems.

The time-dependent gradient structure of a laser-compressed, high-energy-density plasma has been determined using a method based on the simultaneous analysis of time-resolved x-ray monochromatic images and x-ray line spectra from Ar-doped ${\mathrm{D}}_{2}$ implosion cores. The analysis self-consistently determines the temperature and density gradients that yield the best fits to the spatial-emissivity profiles and spectral line shapes. This measurement is important for understanding the spectra formation and plasma dynamics associated with the implosion process. In addition, since the results are independent of hydrodynamic simulations, they are also important for comparison with fluid-dynamic models.

In our experiments, we irradiated solid CH targets with a 400 J, 5 ps, 3 x 10(19) W/cm(2) laser, and we used x-ray imaging and spectroscopic diagnostics to monitor the keV x-ray emission from thin Al or Au tracer layers buried within the targets. The experiments were designed to quantify the spatial distribution of the thermal electron temperature and density as a function of buried layer depth; these data provide insights into the behavior of relativistic electron currents which flow within the solid target and are directly and indirectly responsible for the heating. We measured approximately 200-350 eV temperatures and near-solid densities at depths ranging from 5 to 100 microm beneath the target surface. Time-resolved x-ray spectra from Al tracers indicate that the tracers emit thermal x rays and cool slowly compared to the time scale of the laser pulse. Most intriguingly, we consistently observe annular x-ray images in all buried tracer-layer experiments, and these data show that the temperature distribution is columnar, with enhanced heating along the edges of the column. The ring diameters are much greater than the laser focal spot diameter and do not vary significantly with the depth of the tracer layer for depths greater than 30 microm. The local temperatures are 200-350 eV for all tracer depths. We discuss recent simulations of the evolution of electron currents deep within solid targets irradiated by ultra-high-intensity lasers, and we discuss how modeling and analytical results suggest that the annular patterns we observe may be related to locally strong growth of the Weibel instability. We also suggest avenues for future research in order to further illuminate the complex physics of relativistic electron transport and energy deposition inside ultra-high-intensity laser-irradiated solid targets.

The development of high brightness and short pulse width (200 picoseconds) x-ray lasers now offers biologists the possibility of high-resolution imaging of specimens in an aqueous environment without the blurring effects associated with natural motions and chemical erosion. As a step toward developing the capabilities of this type of x-ray microscopy, a tantalum x-ray laser at 44.83 angstrom wavelength was used together with an x-ray zone plate lens to image both unlabeled and selectively gold-labeled dried rat sperm nuclei. The observed images show approximately 500 angstrom features, illustrate the importance of x-ray microscopy in determining chemical composition, and provide information about the uniformity of sperm chromatin organization and the extent of sperm chromatin hydration.

The use of lasers as the driver for inertial confinement fusion and weapons physics experiments is based on their ability to produce high-energy short pulses in a beam with low divergence. Indeed, the focusability of high quality laser beams far exceeds alternate technologies and is a major factor in the rationale for building high power lasers for such applications. The National Ignition Facility (NIF) is a large, 192-beam, high-power laser facility under construction at the Lawrence Livermore National Laboratory for fusion and weapons physics experiments. Its uncorrected minimum focal spot size is limited by laser system aberrations. The NIF includes a Wavefront Control System to correct these aberrations to yield a focal spot small enough for its applications. Sources of aberrations to be corrected include prompt pump-induced distortions in the laser amplifiers, previous-shot thermal distortions, beam off-axis effects, and gravity, mounting, and coating-induced optic distortions. Aberrations from gas density variations and optic-manufacturing figure errors are also partially corrected. This paper provides an overview of the NIF Wavefront Control System and describes the target spot size performance improvement it affords. It describes provisions made to accommodate the NIF's high fluence (laser beam and flashlamp), large wavefront correction range, wavefront temporal bandwidth, temperature and humidity variations, cleanliness requirements, and exception handling requirements (e.g. wavefront out-of-limits conditions).

A wavefront control system will be employed on NIF to correct beam aberrations that otherwise would limit the minimum target focal spot size. For most applications, NIF requires a focal spot that is a few times the diffraction limit. Sources of aberrations that must be corrected include prompt pump-induced distortions in the laser slabs, thermal distortions in the laser slabs from previous shots, manufacturing figure errors in the optics, beam off-axis effects, gas density variations, and gravity, mounting, and coating-induced optic distortions.