The main feature of x-ray laser research at LULI is the development of a saturated laser at 212 angstrom with a relatively small pump laser of 0.4 kJ in 600 ps. The laser works with the 3p- 3s J equals O yields 1 transition of neon-like zinc, by using the double-pass of amplified radiation in the active medium. Plasma parameters (temperature, density, homogeneity), and x-ray laser emission properties (intensity, pointing angle, divergence, and coherence) have been studied. Lasing action needs the main laser pulse to be preceded by a ten-prepulse train (contrast ratio less than 10³) due to the remnant oscillator. The effect of a single prepulse was investigated as a function of contrast ratio and delay between the prepulse and the main pulse.

Line profiles taking into account ion (Stark) broadening, ion dynamic effect, and electron collisions are calculated for the Al¹⁰⁺ lines at 154.7 and 105.7 angstrom, and for the S¹³⁺ line at 206.5 angstrom in recombination lasers. The first two lines are formed of three fine structure components, while the third is constituted of nine components, and the resulting gain may be defined accordingly. The electron collisions yield an homogeneous broadening, while the Stark interaction with neighboring ions is responsible for an asymmetry of the whole profile. Consistently with the experimental determination of the gain, we calculate the total intensity involving the population inversions of the set of components which contribute to the lasing radiation, and deduce an effective small-signal gain coefficient. We discuss our results and compare them to experimental gains.

Experimental progress in Ne-like Ge x-ray lasers (19.6 nm and 23.6 nm) has been made by using a curved target and multiple-short pulse. The curved target was introduced to compensate x-ray laser beam refraction in a laser produced plasma. The pulse shape of the pumping laser was varied in search for the improvement in the pumping efficiency. For generation of shorter wavelength lasers, the scheme using a curved target pumped with a multiple-short pulse laser was extended to the amplification studies in Ni-like lanthanide elements (Nd, Sm, Gd, Tb and Dy) corresponding to the spectral range of 6 nm to 8 nm.

Current successful approaches for achieving soft x-ray lasing typically require pumping laser pulses of duration approximately ns and energy approximately kJ (collisionally pumped schemes) or approximately ps pulses and powers of approximately several TW (recombination-pumped schemes). For applications, it is important to improve the efficiency of soft x-ray lasers and so reduce the required power of pumping lasers. The effect of pre- pulse on neon-like collisionally pumped lasers has been investigated using the LULI laser (Ecole Polytechnique, France). A small pre-pulse level approximately 10^-3 of the main pulse energy was found to increase the J equals 0 minus 1 neon-like zinc laser output at 21 nm by an order-of-magnitude with a comparable increase in efficiency. A double pumping laser pulse on neon-like yttrium lasing output at 15 nm obtained with the VULCAN laser (Rutherford Appleton Laboratory, England) was also found to increase the x-ray lasing efficiency. With adiabatically cooled recombination lasing, it is shown that approximately 2 ps pulses are optimum for achieving the desired ionization balance for lasing output. The possibility of achieving recombination lasing at short wavelengths on lithium-like ions with longer pulse lasers has been investigated using the ASTERIX laser (Max-Planck Quantenoptik, Germany). These results are presented and interpreted to provide possible directions for improving the efficiency of x-ray lasers.

Neon-like ions are routinely pumped by electron collisional excitation from the ground 2p⁶ state to levels in the n equals 3 manifold, generating a number of different transitions. The experiments are performed in two geometries: foils and slabs. In this paper we examine slab systems using germanium as the prototype medium. The aim is to identify ways in which design modifications can be used to improve the output performance of the x- ray lasers. We examine the role of pump laser pulse modification and target curvature (bending) to reduce refraction effects in the radial direction, and the potential of density wells to produce a guiding effect in the transverse direction.

In this paper we present the results of the first experiments on x-ray laser using a laser- irradiated gas puff target. The gas puff targets were created by pulsed injection of gas from a high-pressure valve through a nozzle into a vacuum. An x-ray laser active medium in a form of an elongated plasma column was produced by the perpendicular irradiation of the gas puff target in a form of a long sheet of gas, created using the nozzle having a linear exit aperture, with the laser beam focused to a line. The x-ray laser experiments were carried out at Garching using the ASTERIX IV high-power iodine laser. Up to 3-cm-long hot and dense plasma columns were produced. Lasing in neon-like argon at 46.9 nm and in nickel-like xenon at 10.0 nm was demonstrated for the first time.

This communication presents the results of wavelength calculations for neon-like ions to verify the resonance condition for a recently proposed x-ray laser scheme which is resonantly photopumped by Ly-(alpha) radiation from H-like Mg and which would lase on several 2p yields 2s transitions in Ne-like Ge. The energies of the excited and ground states were obtained using multiconfigurational Dirac-Fock (MCDF) method with the employment of different methods of the energy functional optimization. Particular attention has been given to the evaluation of the correlation corrections to the transition energies of neon-like ions within the combined MCDF+MZ approach, which uses the results of the MCDF calculations along with the Z-expansion data.

An investigation of the rapid rise time of x-ray emission from targets heated by an ultrashort- pulse high-intensity optical laser was conducted for use as a pump for inner-shell photo- ionized x-ray lasing. Results of x-ray rise times from instantaneously heated Au rod targets show little benefit for using optical pulse widths less than 30 fs. Gain calculations for inner- shell photo-ionized lasing show that large gains can be obtained for pulse widths between 30 and 100 fs. Calculated spectra, using the hydrodynamic/atomic kinetics code LASNEX, from a 1 J, 65 fs FWHM pulse optical laser incident on a structured Au target gave a gain of 11.5 cm^-1 in C at 45 angstrom.

Soft x-ray amplification by optical-field-induced ionization (OFI) of a preformed plasma is investigated. Experimental and numerical results ensure that we have produced a plasma with a significantly lower electron temperature than what is expected by an above-threshold ionization model. In order to explain the results, a two-component plasma model in which relatively high temperature electrons are produced by OFI in a cold electron bath of the preformed plasma is presented. The model indicates that the average electron temperature of the OFI plasma rapidly decreases since a high-temperature part of the electrons escapes from the focal volume without interaction. The initial electrons produced prior to the field ionization which survive after the OFI also significantly contribute to the rapid three-body recombination. Based on the ionization-induced refractive-index change, the pulse propagation of a high-intensity pump laser during the OFI is also discussed.

An experimental evidence is now emerging: high gain coefficients and brightnesses can be easily obtained along the Ne-like (1s²2s²2p⁵)3p ¹S₀ yield 3s ³P₁ (historically anomalous) lasing line, in intermediate-Z [(Ti) 22 less than or equal to Z less than or equal to 34 (Se)] plasmas, using low intensity prepulse techniques. An attempted theoretical explanation of the exact prepulse role in the amplification mechanism is reported, based on recent simulations of a European campaign conducted at the LULI (France) facility.

To obtain the proper conditions for inversion and gain in 'pure' photopumped x-ray laser systems it is normally considered necessary to separate the pump and lasant. This is due to the fact that a plasma which produces adequate pump power is usually too hot and/or dense to sustain lasing. Thus there is a need for separate plasmas at significantly different conditions. In this paper we explore the question of whether the recent rapid development of ultraintense, short-pulse lasers can change this picture by altering the relationship of electron temperature to degree of ionization.

We are developing techniques to shorten the time duration of neon-like x-ray lasers while maintaining their high brightness in order to optimize their usefulness as a plasma diagnostic. Adjusting the duration of the pump laser pulse is shown to directly influence the duration of neon-like x-ray laser transitions. Using slab targets, multiple 100 ps pulses and traveling wave geometry we have shortened the duration of lasing transitions down to 45 ps for both the neon- like germanium and yttrium x-ray lasers. However for the neon-like yttrium laser the intensity of short duration pulses are down two orders of magnitude from the long duration pulses because of limitations of the driving laser. We are presently looking at curved targets and pulse shaping in order to more efficiently pump the Ne-like x-ray laser system and increase the output intensity of the lasing lines. The relative merits of using the germanium x-ray laser at 196 angstrom compared to the yttrium x-ray laser at 155 angstrom are discussed.

Coherent radiation in the extreme ultraviolet and soft x-ray spectral regions can be generated as high-order harmonics by focusing a high-power, short-pulse laser into a jet of free atoms or ions. This process is of basic physics interest, as a probe of the behavior of an atom strongly perturbed by an electromagnetic field. At the same time, the generated radiation has unique properties of short pulse length, high peak power, and high spectral brightness which can be utilized in various applications. The perspectives for optimizing this process, both in efficiency, spectral range, and characteristics are discussed. Examples are presented, illustrating how this new source of coherent radiation can be used in different applications.

The above-threshold ionizations (ATI) in intense laser field are studied by the methods of S- matrix and classical dynamics, respectively. It is shown that from the viewpoint of gauge invariance, the Keldysh theory is more reliable than Reiss theory. Then, the Keldysh theory is developed further to satisfy the law of parity conservation and to give more reasonable results. The ionization rate predicted by classical dynamics is in agreement with tunneling theory as the field strength is near and above threshold field and approaches Keldysh's rate as the field strength is higher than threshold field. The space charge effect is analyzed using the technique of multiple-time-scale perturbation. It is found that the effect on residual energy is great as the half plasma period is larger than pulse length or the plasma density approaches critical density, however, it cannot reduce the ATI energy significantly over whole density range. Finally, it is pointed out that for a given pump laser there may be a density range available for optical field ionization (OFI) x-ray laser over which only the ATI heating plays a role.

We have performed a systematic investigation of lasing on the neon-like 3p - 3s J equals 0 - 1 line in low-Z elements ranging from Cl to Ge using the prepulse technique. Laser pulses from the Asterix iodine laser (lambda equals 1.315 micrometers) were applied to slab targets with a low intensity prepulse 5 ns ahead of the main pulse. Prepulse energies ranged from 0.1% to 15% of the main pulse energy. In all materials lasing on the J equals 0 - 1 line was observed. In vanadium two J equals 0 - 1 lines were found to lase with approximately equal strength. The spatial position of lasing was determined for several materials and two prepulse levels. In addition, the sensitivity of lasing with respect to the mainpulse/prepulse ratio is reported.

Through the use of time-integrated space-resolved keV spectroscopy, we investigate line plasmas showing gain for irradiation using the prepulse technique. The experiments were conducted with the LULI laser of the Ecole Polytechnique, Palaiseau (France), at 1.06 micrometer with prepulse-to-main pulse intensity ratio ranging from 10^-6 to 10^-2. The particular x-ray lasers which were studied were the collisionally excited Ne-like zinc, copper and nickel systems. The effect of the prepulses on plasma conditions are inferred through spectroscopic line ratio diagnostics. It is observed that the value of the electron temperature for each system does not vary significantly with prepulse levels, nor does their spatially resolved profile along the line. The lateral width and density of the Ne-like regions in the plasmas of all three x-ray lasers are seen to increase with the prepulse level.

We present results which show lasing at 79 angstrom in nickel-like neodymium (Z equals 60) when a series of short 100 - 150 ps pulses which are 400 - 500 ps apart are used to illuminate slab targets of neodymium. This multiple pulse technique was first used successfully with germanium and selenium targets where strong lasing was observed on the neon-like 3p yields 3s(J equals 0 yields 1) transitions at 196 and 182 angstrom, respectively. We also present results which use this technique on both higher and lower Z targets of neon-like ions. For the higher-Z ions such as yttrium, zirconium, and molybdenum we observe the usual lasing dominated by the pair of 3p yields 3s(J equals 2 yields 1) transitions as seen in other experiments using single pulse illumination. For lower-Z ions such as iron, nickel, and zinc we see dominant lasing from the 3p yields 3s(J equals 0 yields 1) transition however it is relatively weak for iron and increases with Z to become quite strong for zinc. We present results which show the advantages of coupled slab targets and of using a traveling wave geometry to drive targets with these short pulses. The main result of this work is combining the advantages of the double slab targets, the traveling wave geometry, and the multiple pulse technique to improve the output of the nickel-like neodymium laser at 70 angstrom.

An electron collsional mechanism of the intense line radiation generation in a high density and high electron temperature plasma is elucidated in principle, and demonstrated by numerical simulations. The simulation code is described. Three kinds of targets -- low density targets, solid targets, and cavity targets -- are simulated. The function of electron thermal conduct is discussed. Laser pulse width effects on the intense line radiation generation are numerically investigated, and the optimum pulse width is given. The prepulse behavior on the latter two kinds of targets is observed.

We present recent work on the development of the compact ('table top') soft x-ray lasers (SXLs) using two approaches. In one approach we use low energy Nd/Glass laser (pulse duration, (tau) equals 1.5 nsec, beam energy E equals 3 - 5 J), and in the second approach we use powerful subpicosecond (PSP) laser ((tau) equals 200 fsec, E equals 0.1 - 0.3 J, maximum power density P approximately equal to 2 multiplied by 10¹⁸ W/cm²). We discus generation high gain at 18.2 nm and 13.5 nm in CVI line focussed Nd/Glass laser on a carbon target and the unexplained difficulty to obtain gain-length GL greater than 4.5 in such a configuration. The time evolution of intensities of spectral lines and their correlation with time averaged spectra are analyzed. We also present measurement of plasma refraction as a possible explanation of the limitation of GL. More recently we changed the configuration of this experiment using as a target polyethylene microcapillary with focussing Nd/Glass laser at the entrance of the microcapillary. Very encouraging results were obtained for CVI 18.2 nm line and the possibilities of generation high GL in the near future are discussed.

Low energy, pump-laser pulse lengths of 210 ps are found to create hotter plasmas for low-Z slab targets than 24 ps pulses. A survey of several elements has been conducted in order to identify suitable lasants for a table-top extreme ultraviolet laser. Transverse and longitudinal pumping of the lasant plasma has been investigated.

Operation of a discharge-pumped 46.9 nm Ne-like Ar amplifier at gain length products up to gl approximately equal to 14 is reported. The laser line intensity is observed to increase exponentially for plasma column lengths up to 15 cm, above which it is observed to saturate. The saturation behavior is discussed. Results of the parameterization of the discharge pumped amplifier and the measurement of the soft x-ray laser pulsewidth also are reported. The use of an axial magnetic field, that limits the maximum plasma compression and decreases the density gradients, is observed to cause a moderate increase of the soft x-ray laser intensity and a beam profile that is more Gaussian.

A recently developed laser-produced plasma channel is shown to be a promising means to produce an efficient, compact soft x-ray laser. The channel provides a route for efficient high power laser pumping through optical waveguiding of the pump. The channel also acts as a waveguide for generated soft x-rays, since it has wavelength independent mode structure. Channel creation and guided laser pulses of moderate duration and energy can be highly effective in driving nonequilibrium behavior of these plasmas to generate substantial population inversions.

ASEs of two Li-like Al lines (105.7 angstrom and 154.7 angstrom) were observed using a pulse-train laser with only 2.3 J/cm pumping energy. Gain coefficient of 105.7 angstrom was improved up to over 4 cm^-1 when laser intensity of the second half of a pulse- train laser was reduced to 25% of the first one. The time duration of the gain was about 1 ns within the 3 ns total time duration of pulse-train laser. Also an experiment on double-pass amplification of Al¹⁰⁺ 154.7 Angstrom line was carried out by using an x-ray multi- layer mirror and increase of the line intensity by a factor of 4.4 was observed.

The propagation of the optical laser (pump) used in optical-field ionized recombination x-ray lasing schemes [D. C. Eder et. al, Phys. of Plasmas 5, 1744 (1994)] is examined. A model which self consistently evolves the laser radiation as it ionizes a neutral gas is presented. The model allows for multiple ionization stages and for spatial variations in the neutral gas density appropriate for studying propagation through gas jets and laser evaporated gases. Typical experimental conditions are examined and it is found that ionization induced refraction plays a dominant role in the evolution of the laser pulse.

Flat and spherical Os - Si multilayer mirrors were synthesized and studied. Measured normal incidence reflectivity was 20% at the wavelength lambda equals 380 angstrom. The effect of impurities in silicon layers on the multilayer reflectivity in the ultrasoft x-ray region is discussed.

Mode analyses for the soft x-ray laser (SXRL) cavity has become more sophisticated due to the non-uniform reflectivities of the multilayer cavity mirrors (non-uniform cavity). Analytical investigations show that the effect of mirror surface roughness is greater than that of the incident angle dependence of the mirror reflectivity. The effect of mirror surface roughness on the diffraction losses is notable.

We describe the use of a dispersive Young's slits coherence diagnostic for determining the transverse coherence length of a soft x-ray laser source. W have studied the emission from the Ne-like germanium x-ray lasing lines at 23.2/23.6 nm for comparison with the 19.6 nm lasing line obtained with the use of a prepulse. The effective source size has been determined for both these output modes from the calculated coherence length. We conclude that the use of a prepulse leads to a significant reduction in effective source size at 19.6 nm.

A theoretical investigation has been anticipated to study the possible transverse mode distributions in soft x-ray laser (SXRL) cavity configurations. Numerical simulations show that for a uniform rectangular plane-parallel cavity of Fresnel number 50 the field approaches its stable distribution after 310 transits whereas for a non-uniform unstable cavity it needs only a few transits to approach a stable field.

Collisionally pumped soft x-ray lasers now operate over a wavelength range extending from 4 - 40 nm. With the recent advances in the development of multilayer mirrors and beamsplitters in the soft x-ray regime, we can utilize the unique properties of x-ray lasers to study large, rapidly evolving laser-driven plasmas with high electron densities. Using a neon-like yttrium x-ray laser which operates at a wavelength of 15.5 nm, we have performed a series of x-ray laser interferometry experiments to characterize plasmas relevant to inertial confinement fusion. In this paper we describe experiments using a soft x-ray laser interferometer, operated in the Mach-Zehnder configuration, to study CH plasmas and exploding foil targets commonly used for x-ray laser targets. The two-dimensional density profiles obtained from the interferograms allow us to validate and benchmark our numerical models used to study the physics of laser-plasma interactions.

A novel diagnostic application of XUV lasers has been developed for the study of the hydrodynamic imprinting of laser speckle pattern on directly driven laser fusion targets. A neon-like yttrium laser operating at 15.5 nm is used to probe thin foils of Si irradiated with an SSD smoothed laser at 0.35 mm wavelength and 6 10¹² Wcm^-2 intensity, simulating the initial phase of irradiation of a laser fusion capsule. Measurements of the perturbations in target opacity are made by XUV radiography through the foil. The magnitude and Fourier composition of the perturbations has been determined both before and after Rayleigh Taylor growth, showing the mode spectra of both the initial imprint and the subsequent RT growth.

Over the past several years we have developed a variety of techniques for probing plasmas with x-ray lasers. These have included direct high resolution plasma imaging to quantify laser produced plasma uniformities and moire deflectometry to measure electron density profiles in one-dimension. Although these techniques have been valuable a need existed for direct two dimensional measurements of electron densities in large high density plasmas. For this reason we have worked on developing an xuv interferometer compatible with the harsh environment of laser produced plasmas. This paper describes our design and presents some results showing excellent fringe visibility using the neon-like yttrium x-ray laser operating at 155 angstrom. The coherence properties of this x-ray laser source were measured using interferometry and are also discussed.

We have implemented a variety of stigmatic high-throughput high-resolution spectroscopic configurations in the XUV using focusing multilayer mirrors (MMs), transmission gratings (TGs), and conventional plane reflection gratings. A Type-I 1-m-long spectrograph, which comprises a couple of identical MMs with reflection peaks centered at 180 angstrom and a 1800 line/mm blazed grating operating in the second outside spectral order, has a residual astigmatism of 16 microns, a plate scale of 0.35 Angstrom/mm, a bandwidth of approximately 15 angstrom (FWHM), and a resolution of 24,000 (demonstrated). The solid angle of acceptance is a square which measures 0.03 rad multiplied by 0.015 rad. A density-dependent Stark shift of the 2p⁴3s levels of Mg IV was observed in a laser plasma. A Type-II highly versatile spectrometer, which comprises one focusing MM and a TG used to disperse a converging beam, offers a high throughput and a moderate dispersion, with a plate scale typically in the range 5 - 50 angstrom/mm. With respect to these applications, a number of Mo-Si MMs were synthesized on fused silica substrates (r equals 2000 mm, D equals 60 mm). In combination with a point-like laser-plasma broadband radiation source, the Type-II configuration is by itself inherently suited for spectroscopic characterization of imaging MMs. Our capacity to evaluate the spectral response of MMs has improved dramatically after invoking a 5-cm²-aperture TG with a density of about 1000 lines/mm initially intended for x-ray astronomy. Stigmatic line spectra in a range of 165 - 185 angstrom were obtained in the Type-II configuration, and a resolution of 500 was demonstrated.

Using soft x-ray multilayer mirrors (MMs) and a laser-plasma broadband radiation source, we have implemented a pulsed 0.5-Hz-repetition-rate source of polarized quasimonochromatic radiation in the XUV. The x-ray optical setup comprises a focusing MM at near-normal incidence, a plane polarizing MM at 41 degrees off axis, and a plane multilayer analyzer which can be rotated by 90 degrees with respect to the polarizer. A stigmatic broadband spectrometer comprising a grazing incidence toroidal mirror and a large-aperture (5 cm²) transmission grating (TG) has proved to be useful in spectroscopic characterization of plane multilayer mirrors and the laser-plasma source. The second (reference) x-ray optical channel comprises a focusing MM and serves to monitor the energy of individual pulses. The focusing MMs image the laser-plasma source onto the sodium-salicylate-covered surfaces of flexible 0.7-cm-long light guides 13 mm in diameter coupled through light-guide disks to photomultipliers outside the vacuum tank. The visible and VUV radiation outside the resonance reflection peak is rejected by free-standing Al filters placed before the detectors. The dimension of the x-ray source was measured at 100 microns (width at base) using a CCD array covered with sodium salicylate. The polarizance of the plane MM was measured at 98.2% while the peak theoretical value for this Mo-Si multilayer structure (2d equals 240 angstrom, N equals 25, lambda_o equals 171.4 angstrom, 41 degrees off axis) is 98.75%. The polarized source yields of the order of 5 (DOT) 10⁸ photons per pulse in the resonance reflection band of the MMs.

A dense jet of a plasma consisting of multiply charged ions was generated in the interaction of a laser plasma with a strong external axial magnetic field. It is shown that use of high- luminosity x-ray specroheliograph technique allows us to measure plasma emission spectra with 2-dimensional spatial resolution even in the cases when these spectra have a small intensity. The x-ray spectroscopy and interferometry methods are used to measure plasma parameters distributions. The dependencies of N_e(z) and T_e(z) measured in this paper can be used to calculate the evolution of plasma ionization state during plasma expansion. The quasihomogeneous laser jet, which appears when a laser plasma interacts with an external magnetic field, can be used not only to form an active medium of a shortwavelength laser, but probably also to tackle the urgent problem of transport in a laser ion injector.

Conditions favorable for the achievement of population inversion and gain in laser produced plasmas have been reported on previously. However, the required density profiles can be difficult to achieve in conventional laser heated plasmas. We have explored the feasibility of accelerating plasma with a laser, and letting it collide with a solid density (wall) plasma. The density of the resulting shocked plasma can be controlled and refraction can be reduced in this design. A radiation hydrodynamics model is used to simulate the collision of the laser produced plasma with the wall plasma. In addition, the detailed configuration non-equilibrium atomic populations and the radiative response of both the shocked plasma and the wall plasma are calculated.

The temperature growth of the electron part of plasma due to the electron-ion collisions at the superstrong laser field is investigated. A series of collision process peculiarities at such field are demonstrated. The comparison of developed theory with known experiments is discussed.

The structuring of Z-pinch by a standing laser wave is used to control the process of radiation. The additional relativistic electron beam coaxial with the pinch is supposed for an undulation. The theory of a free electron laser for such an undulator is done for the 'weak' field regime.

In this work we present the results of a numerical investigation of the MHD, atomic and amplification properties of a capillary discharge collisional soft x-ray laser. The comparison of the results of the developed model with the experiment reveal good timing, correct laser pulse duration and temporal features of the amplified line that are similar to those observed in the experiment. Also an encouraging correlation of the laser output angular distribution was obtained. The computed variations of the 3p-3s J equals 0 - 1 ArIX lasing line intensity with discharge parameters have been compared to experiments and show good agreement.

The results are presented of investigations of extremely dense plasmas generated from exploding wires using a new method, monochromatic x-ray backlighting. In this method, shadow images of a bright, dense plasma can be obtained with high spatial resolution using monochromatic radiation from a separate plasma, permitting a major reduction in the required backlighting source power. The object plasma is imaged utilizing x-ray optical elements with spherically bent mica crystals. In particular, shadow images of exploding Al wire plasmas in the 1s²-1s3p line radiation of He-like Al XII were obtained. The images confirm the existence of a low density 'corona' around the wire at an early stage of the wire explosion process, with a dense core at the original wire position. Test experiments were also done with laser produced backlighter plasmas. Spatial resolution of 10 microns was demonstrated. The scheme described here is useful for backlighting extended high density plasmas, and could be a less costly alternative to using x-ray lasers for such purposes.

Capillary discharge with moderate energy contribution (100 - 300 J) working in a pinch regime mode seems to be a promising way to build a really compact and inexpensive soft x- ray laser. A simple snow-plow model of a collapsing plasma, and the statement of experimental efforts toward construction and characterization of an x-ray laser in BYU are presented.

We report x-ray spectra emitted from plasmas generated by focusing 130 mJ/120 fs pulses of the MPQ Ti:Sapphire laser facility on solid targets. Low-Z elements (from Li, Z equals 3 to K, Z equals 19) were chosen as the target materials. By means of two cylindrical lenses a line focus was produced, and in combination with a stepped mirror the laser pulse can be brought to travel along the line focus with the velocity of light. X-ray spectra were observed in the direction of the axis of the line focus by a transmission grating spectrometer coupled to a backside illuminated x-ray CCD. Special attention was given to the emission of those lines which are candidates for lasing. We report systematic investigations with varied laser intensity and line focus geometry. Implications of the observed spectra on the development of a table- top x-ray laser are discussed and plans for similar experiments with an upscaled version of the pump laser are presented.

A collisionally excited transient population inversion XUV-laser on [Ne]-like titanium has been realized using a table top terawatt laser. At the lasing wavelength of 32.6 nm a high gain value of 19 plus or minus 1.4 cm^-1 has been obtained using plasma columns of 2 to 5 mm length.

In order to investigate the possibility of recombination -- pumped lasing in the extreme ultraviolet (XUV) spectral range a fast ablative capillary discharge has been developed. Discharge currents of up to 15 kA with minimum rise-times of 20 ns could be achieved using Li₂CO₃ and SiO₂ capillaries with diameters ranging from 1 mm to 2 mm and lengths ranging from 1 cm to 5 cm. Time-integrated as well as temporally and spatially resolved spectroscopic measurements have been performed. Using a Li₂CO₃ capillary (diameter: 2 mm, length: 5 cm) the Li III (2 $IMP 3) 729 angstrom line showed a significant increase of intensity during the cooling phase of the discharge while its spatial divergence was found to be decreasing. Indication of gain on the O VI (3d $IMP 4f) 520 angstrom transition could be obtained by varying the length of a SiO₂ capillary (radius: 0.5 mm) from 3 cm to 5 cm.