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For direct drive inertial confinement fusion, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing and uniformity of illumination affect the seeding of instabilities at the ablation front. We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an extreme ultraviolet (XUV) backlighter. We use multilayer XUV optics to relay the x-ray laser onto the directly driven foil, and then to image the foil modulation onto a charged coupled device camera. This technique allows us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 mu m drive beam incident on a 3 mu m Si foil using an yttrium x-ray laser on Nova. We present results from a similar technique to measure the imprinted modulation due to a low intensity 0.53 mu m drive beam incident on a 2 mu m Al foil using a germanium x-ray laser at the Vulcan facility. (C) 1997 American Institute of Physics.

The optical reflectance of a strong shock front in water increases continuously with pressure above 100 GPa and saturates at ∼45% reflectance above 250 GPa. This is the first evidence of electronic conduction in high pressure water. In addition, the water Hugoniot equation of state up to 790 GPa (7.9 Mbar) is determined from shock velocity measurements made by detecting the Doppler shift of reflected light. From a fit to the reflectance data we find that an electronic mobility gap ∼2.5 eV controls thermal activation of electronic carriers at pressures in the range of 100–150 GPa. This suggests that electronic conduction contributes significantly to the total conductivity along the Neptune isentrope above 150 GPa.

Simultaneous measurements of shock velocity and optical reflectance at 1064, 808, and 404 nm of a high pressure shock front propagating through liquid deuterium show a continuous increase in reflectance from below 10% and saturating at approximately (40-60)% in the range of shock velocities from 12 to 20mgr;m/ns (pressure range 17-50 GPa). The high optical reflectance is evidence that the shocked deuterium reaches a conducting state characteristic of a metallic fluid. Above 20mgr;m/ns shock velocity (50 GPa pressure) reflectance is constant indicating that the transformation is substantially complete.

We present experimental work exploring displacement and velocity interferometry as high spatial and temporal resolution diagnostics for measuring target preheat and the speed, planarity, and steadiness of a shock wave. A chirped pulse reflectometry experiment is also proposed as a frequency domain alternative for shock speed measurements. These techniques fill a need for high-precision diagnostics to derive accurate laboratory-based equation-of-state data at shock wave-driven pressures directly relevant to astrophysical systems. The performance of these optical laser probe techniques may exceed conventional passive techniques such as temporally streaked recording of optical emission upon shock breakout or side-on streaked X-ray radiography. Results from Nova laser and high-intensity ultrashort pulse experiments are presented.

A high-intensity laser was used to shock compress liquid deuterium to pressures between 0.22 and 3.4 megabars (Mbar). Shock density, pressure, and temperature were determined using a variety of experimental techniques and diagnostics. This pressure regime spans the transformation of deuterium from an insulating molecular fluid to an atomic metallic fluid. Data reveal a significant increase in compressibility and a temperature inflection near 1 Mbar, both indicative of such a transition. Single-wavelength reflectivity measurements of the shock front demonstrated that deuterium shocked above {approx}0.5 Mbar is indeed metallic. (c) 2000 The American Astronomical Society.

A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 {mu}m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10{sup 17} W /cm{sup 2} . Cross sections of the channel were obtained which show a 30 {mu}m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front. (c) 2000 The American Physical Society.

Although high intensity lasers offer the opportunity to explore the equations of state (EOSs) of materials under high energy density conditions, experimental difficulties have limited the application of laser-driven shocks to EOS measurements. However, we have recently performed absolute EOS measurements on the principal Hugoniot of liquid deuterium near one Mbar and of polystyrene from 10 to 40 Mbar. The D2 measurements were made with direct drive; the polystyrene experiments were indirectly driven. The data were sufficiently accurate to differentiate between existing EOS models and were surprising, particularly for D2. The results demonstrate that laser driven shocks can be used effectively to investigate high pressure EOSs.

In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. An x-ray laser is used as an extreme ultraviolet backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and by spectral dispersion for both 0.35 and 0.53 mu m irradiation, and by induced spatial incoherence for 0.53 mu m irradiation. Measurements of the imprinted modulation due to a single optical mode generated by two beam interference, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process are demonstrated. (C) 1997 American Institute of Physics.

The understanding of the collision and subsequent interaction of counter-streaming high-density plasmas is important for the design of indirectly-driven inertial confinement fusion (ICF) hohlraums. We have employed a soft x-ray Mach-Zehnder interferometer, using a Ne- like Y x-ray laser at 155 {angstrom} as the probe source, to study interpenetration and stagnation of two colliding plasmas. We observed a peaked density profile at the symmetry axis with a wide stagnation region with width of order 100 {mu}m. We compare the measured density profile with density profiles calculated by the radiation hydrodynamic code LASNEX and a multi-specie fluid code which allows for interpenetration. The measured density profile falls in between the calculated profiles using collisionless and fluid approximations. By using different target materials and irradiation configurations, we can vary the collisionality of the plasma. We hope to use the soft x-ray laser interferometry as a mechanism to validate and benchmark our numerical codes used for the design and analysis of high-energy- density physics experiments.

We present two-dimensional, high-resolution, spatial images of the 196-{Angstrom} laser emission from the output aperture of a neonlike germanium laser which is created by illuminating a slab target with a series of short 100-ps pulses from the Nova laser. Simulations of the gain which are propagated through the plasma density gradients to calculate the spatial distribution of the laser intensity are compared with the experiments and show good agreement. The importance of refraction in the propagation calculation manifests itself in the laser intensity peaking 150 {mu}m from the target surface, even though the gain peaks 50 to 60 {mu}m from the target surface. {copyright} {ital 1997} {ital The American Physical Society}

X-ray lasers (XRLs) have experimental average gains that are significantly less than calculated values and a persistently low level of spatial coherence. An XRL has been used both as an injected signal to a short XRL amplifier and as an interferometer beam to measure two-dimensional local gain and density profiles of the XRL plasma with a resolution near 1 micrometer. The measured local gain is in agreement with atomic models but is unexpectedly spatially inhomogeneous. This inhomogeneity is responsible for the low level of spatial coherence observed and helps explain the disparity between observed and simulated gains.

In this paper we describe experimental and computational studies of multiple‐pulse‐driven laser plasma, which is the gain medium for a neon‐like yttrium x‐ray laser. Near‐field emission profiles have been measured both with and without reinjection of the x‐ray laser photons to couple with the amplifying medium created by later pulses using an external multilayer mirror. From the temporal and spatial evolution of the near‐field emission profiles we can examine the pulse‐to‐pulse variation of the x‐ray laser plasma due to changes in the hydrodynamics, laser deposition, and the injecting of x‐ray laser photons back into an amplifying x‐ray laser plasma. Using a combination of radiation hydrodynamics, atomic kinetics, and ray propagation codes, reasonable agreement has been obtained between simulations and the experimental results.

A novel diagnostic application of x.u.v. lasers for the study of the hydrodynamic imprinting of laser speckle pattern on directly driven laser fusion targets is proposed and discussed. Initial tests of the diagnostic system are reported.

Collisionally pumped soft x‐ray lasers now operate over a wavelength range extending from 35 to 300 A. These well‐characterized sources have high peak brightness (GeV blackbody temperature) and narrow bandwidth making them ideal for x‐ray imaging and interferometry. We will describe experiments which have used the yttrium neon‐like x‐ray laser operating at 155 A to probe plasmas at electron densities exceeding 4×1021 cm−3. The short pulse duration of this x‐ray laser (∼150 ps) has made it possible to image directly driven thin foils with 1–2 μm spatial resolution. Advances in multilayer mirrors and beam splitters have now also made it possible to develop x‐ray laser interferometers. We will describe initial experiments to probe plasmas relevant to ICF using x‐ray laser interferometry. The progress in the development of short pulse x‐ray lasers (∼30 ps) which are ultimately necessary to extend x‐ray laser diagnostic techniques to higher densities will also be presented.

We report on experiments using traveling wave excitation of neon-like germanium to produce amplification of 3p–3s soft X-ray transitions. The laser pulse consisted of three 100 ps Gaussian laser pulses separated by 400 ps. Targets were 3 cm long germanium slabs. Traveling wave excitation was employed by tilting the wave front of the driving laser by 45 degrees to match the propagation speed of the X-ray laser photons along the length of the target. We compare cases with the traveling wave, with no traveling wave, and against the traveling wave. Significant enhancement of the X-ray laser intensities is observed using the traveling wave technique due to the short gain duration of these plasmas. Gain was inferred from line intensity measurements at two lengths. Our results are compared to a numerical model.

The morphology of the 33.8 A emission from laser‐irradiated targets was studied using a concave mirror with a W/B4C multilayer coating. The mirror had peak normal‐incidence reflectance of 1.8% at a wavelength of 33.8 A. The emissions from a variety of targets were imaged on film with a spatial resolution of 30 μm in the target plane. Radiatively heated, low‐density plastic and silica foams, x‐ray laser targets, and a gas‐filled enclosure were imaged. Several targets were simultaneously imaged at wavelengths of 33.8 and 130 A using two normal‐incidence microscopes.

We have developed compact collisional-radiative models to describe the ionization balance and excitation mechanisms in neon-like selenium x-ray laser plasmas. These models can be used for calculations of the ionization dynamics, detailed emission spectra, and gain coefficients. Careful attention has been paid to indirect processes such as dielectronic recombination, excitation-autoionization, and resonant excitation. We discuss the importance of different atomic processes and model approximations in the ionization balance and gain calculations. These results will be compared to experimental measurements and to previous calculations.

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 authors demonstrate three new X-ray lasers in neon-like zirconium, niobium and bromine which lase on 3p to 3s transitions. By observing the wavelengths and relative intensity of the lasing lines they hope to shred some light on the anomalous lasing in neon-like yttrium, where one laser line dominates the spectrum. In this work they report the wavelengths of five new lasing lines in bromine and six lasing lines each in zirconium and niobium.

We report the observation of high-gain lasing in laser-heated exploding-foil Ag targets at pump irradiances \ensuremath{\ge}6\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W/${\mathrm{cm}}^{2}$. The measured gain coefficients on the dominant Ne-like J=2\ensuremath{\rightarrow}1 transitions are determined to be 9.4\ifmmode\pm\else\textpm\fi{}1.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for (2${\mathit{p}}_{3/2}$)3${\mathit{p}}_{3/2}$\ensuremath{\rightarrow}(2${\mathit{p}}_{3/2}$)3s at 9.9365 nm and 6.${4}_{\mathrm{\ensuremath{-}}1.5}^{+2.0}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for (2${\mathit{p}}_{1/2}$)3${\mathit{p}}_{3/2}$\ensuremath{\rightarrow}(2${\mathit{p}}_{1/2}$)3s at 10.0377 nm. These are the highest gain coefficients yet observed to our knowledge for any short-wavelength laser. Gain is observed on three other Ne-like lines including a J=0\ensuremath{\rightarrow}1 transition at 8.1563 nm, the shortest wavelength yet observed to our knowledge for a Ne-like x-ray laser.

Novel opacity calculations, which treat in detail the spectra of medium-Z ions [Rogers and Iglesias, Astrophys. J. Suppl. Ser. 79, 507 (1992)], produce results that are substantially different from opacity calculations extant in the literature. These new opacities provide solutions to a number of outstanding problems in astrophysics, thus providing an indirect validation of the theory. We report the results of an experiment measuring the photoabsorption in the spectral region from 50 to 120 eV of x-ray-heated iron which corroborate these new opacity calculations.

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 investigated the fringe visibility produced by a Mach-Zehnder interferometer illuminated by a collisionally pumped yttrium x-ray laser operating at 15.5 nm. Fringe visibility varied as a function both of relative path delay and of relative spatial overlap of the beams. This visibility information was extracted quantitatively from several interferograms and analyzed to produce a characterization of the temporal coherence, yielding a gain-narrowed linewidth of 1.3 pm for the 15.5-nm laser transition and spatial coherence consistent with an effective source size of approximately 220 microm +/- 50% at the x-ray laser output.

Using a series of 100-ps optical pump pulses separated by 300 ps, we have produced 45-ps FWHM output pulses in neonlike yttrium operating at a wavelength of 15.5 nm. This is to our knowledge the shortest-pulse collisionally pumped x-ray laser yet produced. The importance of using a traveling-wave pump to increase the output power is also discussed.

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).

We report an observation of soft-x-ray lasing in Ti, at 326.5 \AA{}, based on recent experiments conducted on the Glass Development Laser (1.054 \ensuremath{\mu}m) at the Laboratory for Laser Energetics and the Nova laser (0.53 \ensuremath{\mu}m) at Lawrence Livermore National Laboratory. This Ti laser, which has been identified as a 3p\ensuremath{\rightarrow}3s transition in Ne-like Ti, is unusual in several ways; the J=0\ensuremath{\rightarrow}1, 3p\ensuremath{\rightarrow}3s transition is observed to be the dominant laser line in a Ne-like spectrum, the laser output has a very narrow divergence, and lasing is observed only in experiments where the main optical pulse is preceded by a low-intensity prepulse. We describe the experimental results and present evidence that suggests the gain is enhanced by resonant photopumping of the Ne-like Ti 2p\ensuremath{\rightarrow}4d transitions by 3s\ensuremath{\rightarrow}2p C-like and 3d\ensuremath{\rightarrow}2p N-like Ti lines, which results in lasing on the 3p\ensuremath{\rightarrow}3s transitions in Ne-like Ti.

A transition analogous to the strongest 4{ital d}-4{ital p} nickel-like x-ray laser transition has been observed in cobaltlike ions within the same plasma. Amplified spontaneous emission from Co-like ions has been identified in laser-produced exploding-foil plasmas of Yb and Ta. The Co-like line exhibits similar time history to the Ni-like laser line and has a gain coefficient consistent with a significant Co-like population. The observation of this transition is of interest as fluorinelike analogs to neonlike 3{ital p}-3{ital s} x-ray lasers have never been seen although they are predicted to have gain.

The Ni-like 4d-4p laser scheme has been extended to wavelengths near the K absorption edge of carbon. A gain of 2.3 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ with a duration of 250 psec was observed in Ni-like Ta at 44.83 \AA{} (a wavelength close to optimal for holographic imaging of live cells). Ni-like W produced a gain of 2.6 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ with a total of seven gainlengths of amplification at 43.18 \AA{}. This is the first demonstration of an x-ray amplifier on the short-wavelength side of the carbon K edge, within the ``water window.'' Both lasers should be scalable to coherent power sufficient for holographic imaging and other applications.

We describe a velocity interferometer used to measure the velocity and trajectory of laser driven shocks in liquid deuterium accurately and continuously. This demonstration of velocity interferometry to measure shock velocity and shock trajectory in condensed matter shows strong potential for future studies of laser-driven shocks in transparent media. Accuracy of this technique can be better than 1% in velocity and ±0.2 μm in position during a 10 ns interval.

The X-ray laser is being used at LLNL as a tool for measuring the behaviors of hot dense plasmas. In particular, we have used the 155 /spl Aring/ Yttrium laser to study transient plasmas by both radiography and Moire deflectometry. These techniques have been used to probe plasma at electron densities exceeding 10/sup 22/ cm/sup -3/. The short pulse of this X-ray laser probe has made it possible to directly image ion densities in directly driven thin foils to an accuracy of 1-2 /spl mu/m. In addition, we are constructing an X-ray laser interferometer using multilayer beamsplitters. If successful, this will lead to /spl mu/m spatial resolution measurements of electron densities in plasmas.

Collisionally pumped X-ray lasers have been demonstrated to have sufficient energy, and narrow bandwidth to make them one of the brightest laboratory X-ray sources available. Furthermore, with their relatively small source size and narrow divergence they have enough spatial and temporal coherence to be applied in interferometric applications. A program to develop plasma diagnostics based on the X-ray laser probing has been underway at Lawrence Livermore National Laboratory (LLNL) for several years.

This paper describes our theoretical, numerical, and experimental development of short-pulse-duration, high brightness, and enhanced coherence X-ray lasers (XRLs) as sources suitable for applications as imaging diagnostics for laser plasmas.

We present equation of state points for iron, in the pressure range 10-45 Mbar, the first obtained with laser-driven shock waves. The experiment has been performed with the high energy laser Phebus, optically smoothed with Kinoform phase plates. Our results double the set of existing experimental data at very high pressures showing good agreement with the predictions of the quotidian equation of state model and with previous results.

Hugoniot measurements of liquid molecular deuterium were made using laser-driven shocks. The equation-of-state data are in agreement with the dissociation model (AIP)

Results of a niobium absorption experiment are presented that represent a major step in the development of techniques necessary for the quantitative characterization of hot, dense matter. The general requirements for performing quantitative analyses of absorption spectra are discussed. Hydrodynamic simulations are used to illustrate the behavior of tamped x-ray-heated matter and to indicate potential two-dimensional problems inherent in the technique. The absorption spectrum of a low-Z material, in this case aluminum, mixed with niobium provides a temperature diagnostic, which together with radiography as a density diagnostic fully characterizes the sample. A discussion is presented of opacity calculations and a comparison to the measurements is given that illustrates the need for experiments to provide a critical test of theory. The experimental technique is placed in context with a review of previous measurements using absorption spectroscopy to probe hot, dense matter. It is shown that the overall experimental concepts, although understood, were not always achieved in previous experiments. \textcopyright{} 1996 The American Physical Society.

The reliability and characteristics of collisionally pumped soft x-ray lasers make them ideal for a wide variety of plasma diagnostics. These systems now operate over a wavelength range extending from 35 to 400 {Angstrom} and have output energies as high as 10 mJ in 150 ps pulses. The beam divergence of these lasers is less than 15 mrad and they have a typical linewidth of {Delta}{lambda}/{lambda} {approximately} 10{sup -4} making them the brightest xuv sources available. In this paper we will describe the use of x-ray lasers to probe high density plasmas using a variety of diagnostic techniques. Using an x-ray laser and a multilayer mirror imaging system we have studied hydrodynamic imprinting of laser speckle pattern on directly driven thin foils with 1-2 {mu}m spatial resolution. Taking advantage of recently developed multilayer beamsplitters we have constructed and used a Mach-Zehnder interferometer operating at 155 {Angstrom} to probe 1-3 mm size laser produced plasmas with peak electron densities of 4 x 10{sup 21} cm{sup -3}. A comparison of our results with computer simulations will be presented.

The reliability and characteristics of collisionally pumped soft X-ray lasers make them ideal for a wide variety of plasma diagnostics. These systems now operate over a wavelength range extending from 35 to 400 /spl Aring/, and have output energies as high as 10 mJ in 15 ps pulses. The beam divergence of these lasers is less than 15 mrad and they have a typical linewidth of /spl Delta//spl lambda///spl lambda/-10/sup -4/ making them the brightest XUV sources available. In this talk I'll describe our use of X-ray lasers to probe high density plasmas using a variety of diagnostic techniques. Taking advantage of recently developed multilayer beamsplitters we have constructed and used a Mach-Zehnder interferometer operating at 155 /spl Aring/ to probe 1-3 mm size laser produced plasmas with peak electron densities of 4/spl times/10/sup 21/ cm/sup -3/. A comparison of our results with computer simulations is presented. We have also used X-ray lasers and a multilayer mirror imaging system to study hydrodynamic imprinting of laser speckle patterns on directly driven thin foils with 1-2 /spl mu/m spatial resolution. Results from these experiments as well as our use of X-ray laser moire deflectometry to measure the electron density profile in ICF hohlraums are discussed.

We have developed and used for the first time a soft x-ray interferometer to probe a large laser-produced plasma with micron spatial resolutions. A neonlike yttrium x-ray laser operating at 155 A was combined with a multilayer coated Mach-Zehnder interferometer to obtain electron density profiles in a plasma produced by laser irradiation of a CH target. The measured electron density profile has been compared to hydrodynamic simulations and shows good agreement near the ablation surface but some discrepancy exists at lower densities.

We have employed an x-ray laser (XRL) in a multilayer mirror optical system to obtain high resolution side-on radiographs of laser-accelerated and x-ray heated metallic foils. The XRL served as a bright monochromatic backlighting source. This is the first time such images have been made with a resolution on the few-micron scale. In spite of the fact that the drive laser beam was smoothed, small-scale breakup of the accelerated foil was observed. Slightly asymmetric expansion of x-ray heated foils was predicted and observed indicating near-volumetric heating.

Collisionally pumped soft x‐ray lasers now operate over a wavelength range extending from 35–350 A. These well characterized sources have high peak brightness (Gev blackbody temperature) and narrow bandwidth making them ideal for x‐ray imaging and interferometry. The yttrium neon‐like x‐ray laser operating at 155 A has already been used to image directly driven foils with 1–2 μm spatial resolution and probe plasmas at electron densities approaching 1022 cm−3 with moire deflectrometry. Advances in multilayer mirrors and beam splitters have now also made it possible to develop x‐ray laser interferometers. We will describe initial experiments to develop x‐ray laser interferometry for probing plasmas relevant to ICF.

This paper describes our recent experimental and computational development of short‐pulse, enhanced‐coherence, and high‐brilliance x‐ray lasers (XRLs). We will describe the development of an XRL cavity by injecting laser photons back into an amplifying XRL plasma. Using a combination of LASNEX/GLF/SPECTRE‐BEAM3 codes, we obtained good agreement with experimental results. We will describe the adaptive spatial filtering technique used to design small‐aperture shaped XRLs with near diffraction‐limited output. Finally we will discuss issues concerning the development of high‐brilliance XRL architecture, with emphasis on scaling the XRL aperture. Combining these advances in XRL architectural components allows us to develop a short‐pulse, high‐brilliance, coherent XRL suitable for applications in areas such as biological holography, plasma interferometry, and nonlinear optics.

We describe initial experiments to produce soft x‐ray interferograms using a collisionally‐pumped Y soft x‐ray laser at 155 A as the probe source. Successful operation of the interferometer requires tight alignment tolerances: spatial overlap of the beams to within 50 μm, and temporal overlap to within a 150 μm path difference. Beamsplitter vibrations were found to be a strong factor influencing the quality of the interferograms.

Fresnel zone plates are now routinely used to produce two dimensional x‐ray images of organic and inorganic specimens. We describe one possible approach of achieving three‐dimensional x‐ray imaging which utilizes non‐circular Fresnel zone plates. This approach is ideally suited for applications in the x‐ray laser community where specimen and zone plate alignment must be performed off lines.

Traveling wave excitation has been shown to significantly increase the output intensity of the neon-like germanium x-ray laser. The driving laser pulse consisted of three 100 ps Gaussian laser pulses separated by 400 ps. Traveling wave excitation was employed by tilting the wave front of the driving laser by 45 degrees to match the propagation speed of the x-ray laser photons along the length of the target. The authors show results of experiments with the traveling wave, with no traveling wave, and against the traveling wave and comparisons to a numerical model. Gain was inferred from line intensity measurements at two lengths.