The spectra of multicharged ions produced by laser irradiation of moderate-Z (Z ≈ 40) and high-Z (Z ≈ 75) elements are dominated by tne dipole resonance lines of the isoelectronic sequences of neon and nickel, respectively. These spectra have been obtained for a large number of elements at the GRECO-ILM laser facility using both 0.26 μm and 0.53 μm laser wavelengths and 10¹³-10¹⁵ W/cm² laser intensities. In addition to numerous electric dipole transitions, electric quadrupole resonance transitions have been measured and identified. The relativistic parametric potential method and the unresolved transition array (UTA) formalism support the identifications. Applications to laser-plasma diagnostics and laser-plasma X-ray sources will be emphasized.

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.

We report a new diagnostic technique that allows us to measure simultaneously time- and space-resolved x-ray spectra of high-powered laser-produced plasmas. The simultaneously time- and space-resolved x-ray spectra were measured using a multiframe, electrically-gated, imaging x-ray spectrometer with 100 ps time resolution, and an x-ray streaked crystal spectrograph with a spatial imaging slit. A 4-frame holographic interferometer was used to measure the electron density profiles of the plasma. All three instruments were run simultaneously and allow for the first direct comparison of electron density spatial profiles determined via interferometry and spatially-resolved emission spectra from the plasma at the same instant in time. The CHROMA laser facility at KMS Fusion has been used to irradiate a variety of microdot targets. These targets include aluminum and magnesium microdots as well as targets consisting of a mixture of bromine and magnesium. Preliminary comparison between density and temperature profiles derived from line-intensity-ratio techniques and determined from holographic interferometry and free-bound continuum measurements are presented.

Extreme ultraviolet (XUV) emission from hot, dense plasmas produced by the OMEGA laser at the Laboratory for Laser Energetics has been studied using a 3 meter grazing incidence spectrograph. Targets were composed of elements with atomic numbers in the range Z=14-92. These targets were irradiated by the 24 beams of the OMEGA laser focused to intensities between 10 14 wicm2 and 5 x 1016 W/cm2. High-resolution spectra were recorded in the wavelength region 6 I to 370 A, and spectral lines have been identified from ions in the isoelectronic sequences H I through Zn I. Based on these spectra, we have investigated relativistic and quantum electrodynamic (QED) effects in highly-charged ions, XUV continuum emission from high-Z plasmas, XUV spectroscopy of interest for x-ray laser research, and electron temperature and density in the coronal plasma.

The presence of intermediate ionization stages of a 1( ma can give rise to absorption lines corresponding to ini tum number 1 and 2. These transitions only occur when thi ions belong to helium-like to fluor-like isoelectronic s( in silicon laser produced plasmas (1). They have been der shock heated plane targets (2) and of the compressed she:

An experiment to measure the distribution of ionization states in an argon plasma proliaced by irradiating a gas-jet with 351-nm radiation from the OMEGA laser is described. The gas-jet was provided by Plasma Research Corporation. Its low divergence makes it possible to create a disk-shaped plasma region 1.5 mm diam x 1.5 mm thick over which the temperature and density are slowly varying. The experiment was performed at the Laboratory for Laser Energetics, University of Rochester, as part of the Department of energy's National Laser Users Facility Program. Eight beams of 60 J each were used to teat the argon gas-jet plasma. In the present experiment, a plasma temperature of about 65 eV was achieved at an electron density of about 1.0 x 1018. Lines in argon charge states VIII-XI have been ileatified in the spectra, and the results are compared with theoretical models which ,directly solve the time-dependent charge-state rate equations. It was found necessary to preionize the argon in order to couple in sufficient energy from the laser to produce a plasmasma.

Transport of intense soft x-ray radiation generated from a laser-produced plasma through a high density material is studied. Experimental observations of ionization burn-through and shock wave generation arising from radiation transport through solid density aluminum are reported. From the experimental results, ablation pressure due to soft x-ray driven ablation is determined.

Conversion of 351-nm laser light to soft x-rays has been studied using spherical gold targets irradiated at 5 x 1012-4 x 1015 W/cm2. Spectra and time histories of sub-keV and M-band emission are presented. Results have been compared to detailed models (LASNEX) to better determine the dynamics of the plasma processes which lead to x-ray emission.

A detailed understanding of the interaction of laser light with high Z materials is important for the development of indirect drive inertial confinement fusion. To improve our understanding of the interaction of 0.35 um light at intensities between 1014 and 1015 W/cm2 with high Z materials, we have performed a variety of experiments to address important physics issues. Hydrodynamics and ablation, transport Processes, and x-ray conversion have been studies with thin Au dot targets and Au and Be mixture taraets.

Measurements of x-ray conversion efficAncies9have been made for plasmas produced by KrF laser pulses at intensities of 2.5-7.5x10 ''W cm Initial measurements of x-ray fluence have been made using a simple set of filtered x-ray diodes and an x-ray calorimeter for targets with atomic numbers from 4 to 82. More detailed measurements have been made of three elements: aluminum, titanium and gold. These have included measurements of the angular dependence of emission, the spectral characteristics of emission in the 100-1000 eV range and time dependent measurements of the spectrum using an x-ray streak camera. The angular and spectral characteristics have been used to more accurately determine the energy conversion efficiency for these elements.

The present status of the theoretical and experimental studies on the laser generation of soft x-rays in open and closed geometry, performed at the Max-Planck-Institut fiir Quantenoptik (MPQ) at Garching , is reviewed.

Preliminary characterisation of a laser generated plasma source of soft x rays in the wavelength range of approximately 40 to 60 A has been undertaken using a Nd:YAG laser emitting 0.5 J at a wavelength of 1.064 itm radiation in 8 ns pulses at 20 Hz repetition rate. The effects upon x-ray production of moving the target through focus and the consequences of target cratering have been investigated. Results from these experiments have been used for preliminary optimisation of the process of contact replication of test specimens, resulting in the replication of feature sizes of 700 Å.

The observation of soft x-rays from a tungsten plasma produced by intense subpicosecond laser pulses is reported. X-ray emission up to several keV photon energy was observed with just a few millijoules of laser energy. From correlation measurements of the x-ray signal from a plasma generated by two consecutive pulses we obtained an initial information on the dynamics of the plasma and the x-ray emission.

Laser-produced tungsten plasmas have been investigated in respect to their suitability as radiometric source standards covering the wavelength range from 7 nm to 100 nm. The laser system used was a Nd:YAG/Glass system working at X = 1.064 pm with a pulse duration of 17 ns (FWHM) and pulse energies ranging from 100 mJ to 800 mJ in combination with a focusing system of 85 mm focal length. The time-integrated spectral concentration of radiant intensity has been determined with an overall uncertainty of 8 % using the electron storage ring BESSY as a primary standard. Within this uncertainty reproducebility in radiation emission was demonstrated over periods of several months at specific operating conditions. The spectral radiati9p emission reached its maximum at 16.5 nm. For 800 mJ pulse energy an emission of 3.5 x 10 photons/nm/sr was found at 16.5 nm. At present the development of a low cost, single stage YAG-laser based, transportable standard is under way.

Several X-ray and XUV diagnostic techniques have been stimulated by research on high density plasmas produced in laser fusion, by X-ray laser studies, astrophysics and by studies using synchrotron generated X-rays. Most of these techniques can be crudely divided in two classes : The first class includes in particular time resolved spectroscopy and one dimensional (1D) space-time imaging. A comprehensive description of several time resolved devices can be found in Ref. 1. The se-cond class includes purely space resolved imaging systems. This paper in no way attempts to review all progress in X-ray diagnostics. However since most of the diagnostic devices use some imaging system, generally of microscope type, we shall review the principal two-dimensional (2D) or three-dimensional imaging systems with emphasis on the relative image properties and on the progress introduced by the advent of X-ray multilayers.

A grazing incidence concave toroidal mirror, is used to relay soft X-rays and reduce the debris, generated by a laser-plasma source, to the window of a "wet-cell holder" built for the purposes of soft X-ray contact microscopy of hydrated, living cells. It is shown that algal material remains in a hydrated state during and after the imaging process, however this process is complicated by many problems concerned with the polymers which make up the recording medium.

Double reflections in single crystals and in two crystals in series may be used to obtain monochromatic x-ray images of x-ray sources. Thus ion distributions of the various ions in laser produced plasmas and other hot plasmas may be obtained. Moreover, strictly monochromatic parallel beams of x-rays, produced with this method from e.g. a synchroton source, may he used for lithography, with the mask not necessarily in close contact with the photoresist. The beam will be parallel enough not to be broadened by the distance between them. Theory yields a spatial resolution of 100Å at 1.5 wavelength, with the distance between mask and photoresist of about 1 mm. Similar results with two crystals in series may be obtained, if the two planes of reflection, each containing the incoming and outgoing beam, are not parallel. The angular broadening of a monochromatic beam obtained by either method of double reflection is given as function of diffraction width of the second reflecting crystal plane and of the angle between the planes of reflection.

We present a small laser facility set up to calibrate and check X-ray instrumentation. The laser is a 4J-4ns neodymium YLF laser working at 1.053 gm and 0.53 gm with 50% efficiency conversion. We present X-ray pinhole images of Al and Copper created plasmas using different filters to obtain radiation from 1 to 2 keV. We present also V-UV images at different wavelengths from 100 to 300 ang. showing the large spectral range emissibity of the plasma used as source. In a further step crystal spectrograph and grating spectrograph will be set up around this source to select narrow band emission and to check for example the reflectivity of multilayered mirrors, the spatial resolution of V-UV objectives as Schwarzschild microscopes.

We have measured the response of W/C multilayers to x-ray fluxes on the order of 150 MW/cm² using laser generated plasmas and found that these multilayers will maintain near peak reflectivity for at least 1 ns but are eventually destroyed. A description of the experiments and data analysis methods is given. The results of the experiments will be compared with hydrodynamic code simulations.

Tri-dimensional imaging of X-rays emitted by laser induced plasmas can be performed by Coded Aperture Imaging (C.A.I.) using a "multislit" code and linear CCD detectors in order to provide real-time imaging. We present the realization of this Multislit CCD camera.

A time resolving XUV spectrograph has been developed for x-ray laser research. A grazing incidence flat field grating is coupled to a soft x-ray streak camera to provide high temporal resolution over a large spectral range. Wavelengths between 50 Å and 400 A are focused onto a flat field, allowing detectors to be easily coupled to the spectrograph. Time resolved spectra covering any ''100 A window within flat field can be recorded using a streak camera. The spectrograph and detector were absolutely calibrated in the XUV spectral region using synchrotron radiation. The instrument and its characterization will be described. The wavelength range of the spectrograph has been extended to approximately 11 R through the use of a higher periodicity flat field grating. Preliminary spectroscopic results will be presented.

An apparatus for time-resolved X-ray absorption measurements is discussed. The apparatus consists of a 15 ns, 20 J Nd:YAG/glass laser system, a polychromator for soft X-rays and a multichannel detector system. X-ray emission spectra of a laser produced plasma (LPP) for 15 different target materials are shown. Time resolved X-ray absorption measurements (90-190 eV) on clouds of Si particles, produced by laser irradiation of bulk Si, are presented. From these measurements the following results were obtained: Clusters are formed at an irradiance as low as 3.0 J/cm2; at an irradiance of 14 J/cm2 ionized species up to Si 4+ are formed; at an irradiance of J/cm2 at 15 ns pulse duration, a Si layer thickness of 80 Å is removed.

Photoconductive detectors (PCDs) offer an attractive alternative for the measurement of pulsed x-rays from laser produced plasmas. These devices are fast (FWHM '000 ps), sensitive and simple to use. We have used InP, GaAs, and Type IIa diamond as PCDs to measure x-rays emission from 100 eV to 100 keV. Specifically, we have used these detectors to measure total radiation yields, corona temperatures, and hot electron generated x-rays from laser produced plasmas.

Over the last few years new technologies for the production of fast, high voltage pulses have emerged. The production of kilovolt amplitude pulses has long been a requirement for many high speed camera systems and the appearance of convenient and fast bench top pulsers has greatly sped up shutter tube development in the last two to three years. Although suitable electrical pulses have been produced for some time by large facilities such as electron LINACs and laser driven photoconductive switches, the ability to tinker on the bench top, away from the constraints of a large system, has allowed several new shuttering schemes to progress very rapidly.

We present time resolved images of the rear side of thin foils illuminated by a 0.26 pm laser with an intensity of several 1014 W/cm2. Aluminium and gold targets of several thicknesses are used. The images are recorded with 2 Schwarzchild Microscopes having their peak reflectivity at 304 A and 155 A. Comparison with simulations shows that the expected temperature put these wavelengths of imaging around the peak emissivity of the rear side of the thin illuminated targets.

X-ray transmission photocathodes are limited in sensitivity at soft x-ray energies (⪅100 eV) due to absorption in the photocathode substrate. We report on the design of a streak camera incorporating a reflection mode photocathode which will extend the detectable spectral range through the VUV. The slot aperture in the accelerating electrode of our standard large format x-ray streak cameras provides a clear access window to the photocathode. This instrument will be used to detect the soft x-ray spectrum as dispersed by an x-ray transmission grating.

A conically-curved crystal x-ray spectrograph of a design proposed previously has been implemented, and combined with an x-ray streak camera to produce a streak spectrograph. The spectrograph design differs from more common curved crystal designs in that it collects a solid angle of x-rays and produces a line focus spectrum perpendicular to the axis from the source. Initial efforts using a mica crystal have produced a time-resolving spectrograph of especial interest to time-resolution of weak laser-plasma emission, having moderate spectral resolving power (λ/Aλ 600-1000), collection efficiency 50-100 times that of a comparably deployed planar crystal spectrograph and streak camera, and time resolution of 20-40 ps. The device is demonstrated in experiments time-resolving the temperature and density of thin aluminum signature layers isolated in spherical plastic targets.

Laser-produced plasma continuum X-ray sources have been generated using the high power VULCAN glass laser system at the SERC Rutherford Appleton Laboratory, and used for a range of X-ray absorption spectroscopic measurements. EXAFS (extended X-ray absorpticn fine structure) spectra have been recorded in transmission mode for various low Z materials using both time-integrated and time-resolved techniques, and experiments have been performed to study ion correlation effects in a strongly coupled plasma via nearest neighbour distance measurement. A reflection geometry has also been demonstrated in which grazing incidence reflection EXAFS (ref lEXAFS) spectra have been recorded, and experiments performed to investigate surface effects occurring during pulsed laser irradiation of thin nickel overlays on silicon. An assessment is made of the usefulness of such experimental methods, and comparisons made with alternative techniques.

Plasma X-ray sources for biological microscopy in the water-window have been produced by focusing tige 200 3, 50 ns Sprit q KrF laser onto carbon targets at irradiance between 2.2 x 10" W/cm4 and 3.7 x 10i3W/cm. Absolute measurements of X-ray production have been made using a calibrated, vacuum X-ray diode detector. A peak conversion efficiency . 10% is measured from KrF laseri)Tight tcto wate-window X-rays at 280 eV < hv < 530 eV for a target irradiance . 1 x x 10 W/cm'. Some measurements with gold and tungsten targets give conversion efficiencies 2$25% at a similar laser irradiance.

The use of a laser produced plasma as an x-ray source for high resolution microradiqgraphy has several advantages over conventional x-ray sources: a very small source size (<100 pm in diameter) and a pulsed exposure with a less than 1 ns duration. The former provides the possibility of high spatial resolution, and the latter produces high temporal resolution. It has been proposed that the pulsed exposure is ideal for imaging living biological specimens. In order to obtain high resolution images, modern microradiography uses high molecular wight polymers (photo-resists) as the photochemical detector on which a surface relief image is formed. Therefore, one of the factors affecting image resolution is the surface roughness of the resist. This paper reports the surface roughness on the resist polymethyl methacrylate (PMMA) which has been exposed to the radiation from a laser-produced plasma x-ray source. The surface roughness was investigated by transmission electron microscopy using a metal replica technique.

Experiments to demonstrate the feasibility of a small laser for x-ray lithography are discribed. Resist exposure experiment was performed by x-rays from a plasma produced by a KrF laser, 0.6 J/ 20 ns. With 50 shots exposure, a very fine pattern of 0.5 μm line & space was printed onto a resist EBR-9 at 3 cm from an iron plate target. The conditions for a laser-plasma to be a practical source for x-ray lithography are discussed.

Laser-plasma X-ray sources suitable for lithography with silicon-substrate masks are generated by focusing 2a low energy, repetitive, commercial KrF laser onto targets at irradiances 101N/cm2. Conversion efficiency to X-rays at hv m 1 keV has been measured as a function of target irradiance and target atomic number. The best quantitatively measured conversion efficiency of 0.3% is obtained using a Ni target (Z = 28). A repetitive (2Hz) Ag target X-ray source is used to demonstrate microlithography by printing 0.5 pm lines and spaces into EBR-9 resist.

Laser created X-ray sources have been investigated both theoretically and experimentally using X = 1.06 pi and X = 0.26 wm and short pulses (T = 0.5 nsec). We also report the first detailed X-ray measurements using a low energy commercially available KrF laser (τ = 25 nsec). The conversion efficiency is given for various target atomic numbers and a large range of laser intensities. Finally, we introduce lithographic considerations and examine the laser requirements for an X-ray lithography source acceptable for industrial applications.

When a crystal is annealed or shocked the spacing of the interatomic planes is altered, and a measurement of the lattice spacing can yield information on the temperature or compression respectively. We have used the JANUS research laser at LLNL to perform such measurements of transiently strained crystals. JANUS is a two beam laser system, with separate synchronized oscillators for each beam. One beam of the laser, containing ~10 -100 J of 1.06pm light in a pulse of 1 ns FWHM, was focused to a 3.9 cm diameter spot on the surface of a silicon crystal; the crystal was either annealed or shock-compressed, depending on the absence or presence of a variety of thin coatings applied to the crystal surface. At some time during or after the perturbing pulse, the second synchronous but delayed laser beam, containing ~10 J of 0.53pm light in a pulse of 100 ps (FWHM), was focused to a 40pm diameter spot onto a separate target containing calcium, potassium, and chlorine. Thus, a short pulse of the helium-like line radiation of these atoms was produced, and this radiation was Bragg diffracted from the surface of the strained crystal. Measurements of the change in Bragg angle, caused by thermal expansion or shock compression, gives a direct measurement of one component of the strain within the crystal. A single laser shot gives recordable x-ray levels. A number of shots at different irradiances and delay times gave information about the lattice spacing as a function of time. The potential applications of such results is discussed.

A scheme for a resonantly pumped, laboratory x-ray laser has been developed and the results from preliminary investigations are presented. The scheme uses a gas-jet target, developed by G. H. Dahlbacka of Plasma Research Corp., as the lasing medium. The resonant pump for the scheme comes from a solid target which can be heated to the appropriate temperature by the remaining laser light after it heats the gas medium. The particular scheme that will be presented uses a Be IV 2μ-* is transition to pump a principal quantum number 2 -*4 excitation in Ne VII, with the objective of creating a population inversion between the Ne VII 4 and 3 levels. Time-integrated x-ray emission spectra from the Ne plasma, Ne spectra with and without pumping by radiation from the Be plasma, and calculations which predict the effects of the pump upon the target plasma, and which are compared with the experimental results, are described.

Significant progress toward the goal of producing high Power, high coherence x-ray lasers has been made. Lasing at wavelengths as low as 66 A has been achieved in a nickel like laser scheme which is scalable to sub-44 Å wavelengths. In addition, x-ray laser cavities, x-ray holography, and an applications beamline have been demonstrated.

The sequence of Li-like ions represents an attractive avenue to progress to laser action at soft X-ray wavelengths shorter than those of current X-ray lasers1,2 (see also Refs. 3-6). We are exploring the possibilities for laser action at 15.4 nm in Li-like A1XI and 12.9 nm in Li-like SiXII in a magnetically confined recombining plasma. A ti 1 kJ CO2 laser is focussed onto an aluminum or silicon target assembly and the resulting plasma confined in a solenoidal magnetic field of up to 90 kG. This approach is similar to our previous work on hydrogen-like carbon, CVI, which led to lasing action on the n = 3 to m = 2 transition at 18.2 nm. For lithium-like ions we measure a maximum gain-length (gL) on the 4f-3d transition, of gL Rs 3-4 at 15.4 nm and gL % 1-2 at 12.9 nm. The 18.2 nm laser has been applied to microscopy and first results from a soft X-ray laser microscope are presented.

Recent x-ray laser research carried out at the Rutherford laboratory has concentrated on examining recombination pumping in H-like and He-like ions. Laser irradiation of thin fiber targets establishes a rapidly expanding plasma column in which population inversions are created during the recombination cascade. Experimental results in H-like carbon and fluorine systems will be presented along with the preliminary analysis of Li-like Al and Cl systems.

A recent series of experiments have provided spatially resolved near field images of several candidate x-ray lasing transition in neon-like, nickel-like, and hydrogen-like ions from laser-produced plasmas. From these time-gated, spatially, and spectrally re-solved measurements the source size for the J=0-1 and the J=2-1 transitions in Ne-like selenium have been determined. Source regions as small as 50 pm have been observed on transitions with gain-length products >9. In addition, we have obtained the first experimental evidence for the amplification of spontaneous emission in the nickel-like ions of europium and ytterbium. Gains of order 1 cm-1 I,dnd gain-length products of up to 3.8 are observed on the J=0-1,4d-Lip transitions in Eu+35 at 65.83 and 71.00Å. Analogous transi tions in Yb+42 have been identified and some evidence for ASE has been observed.

Laser produced plasmas have been extensively used as suitable media for soft x-ray lasers. Recently, amplified spontaneous emission at the 130-200 Å range has been observed in experiments involving laser-produced plasmas.1-3 Gain coefficients of about 5^-6 cm-1 were measured on 2s²2p53p - 2s²2p53s transitions in neon-like selenium, yttrium and molybdenum.

In a low-Z plasma subjected to photoionizing radiation, stationary inversions on hydrogenic level populations occur. A collisional-radiative model is used to calculate gains for the case where the electron temperature is determined by radiative cooling alone, and for the case where additional electron cooling is provided. In the first case, measurable gain on the Balmer-a line is found. In the second case, the Balmer-a gain is dramatically enhanced and, moreover, sizeable gain on the Lyman-a line is predicted.

By irradiation of thin foil targets with line-focused 526nm laser, XUV amplifications have been observed in the following transitions : C 3d-2p 182A, 0 3d-2p 102Å and al 5f-3d 105Å and 5d-3p 104A. New diagnostic setup for time-resolved XUV spectroscopy for x-ray laser research is also presented.

The new geometries for x-ray laser targets described in the preceding paper were experimentally examined at the Laboratory for Laser Energetics. These target are proposed as improvements on the single foil geometry used for x-ray laser generation at other laboratories.1-5 We describe a series of experiments which were aimed at measuring the spatial density profile of Ne-like nickel plasmas produced by double-foil targets. The initial experiments utilized a 1.5 mm line focus which was of sufficient length for studying the hydrodynamic behavior of the proposed new geometries. Results of experiments, using a 1-cm line-focus, which indicate gain in these targets are also presented. In all cases the target material was nickel.