We present our recent efforts to produce X-ray lasers in the 200 angstroms range by using the moderate power drive of the LULI facility in Palaiseau. The 4 - 5 transitions of Li-like sulfur exhibit large gain-length products in recombining plasmas, and appear to be less sensitive to plasma non-uniformity than the 3 - 4 and 3 - 5 transitions previously studied. From numerical simulations this is likely due to smaller radiative and collisional excitation from 4f than from 3d levels. In collisional scheme, neon-like zinc gives analogous results to similar works on other elements for the 3p - 3s, J equals 2 yields 1 transitions, but the J equals 0 yields 1 transition shows a surprisingly large gain coefficient of 4.9 cm^-1. From a detailed comparison of time-dependent intensities of the J equals 0 yields 1 and the J equals 2 yields 1 lines, we conclude that transitions from J equals 0 and from J equals 2 are not emitted in the same region of the plasma.

It is shown that curved slab targets are effective in compensating x-ray refraction due to electron density gradient in the expanding plasma. Significant improvement in the beam divergence and laser intensity has been observed. Soft x-ray laser of 1 mrad divergence has been generated in double- pass amplification of a collisionally-excited Ne-like Ge laser with the curved target. Generation of a polarized beam with a polarizing half cavity is described. Initial results of in-line holography as well as Fourier transform holography using the Ge laser as the light source are also presented.

An injector-amplifier architecture for XUV lasers has been developed and demonstrated using the Ge XXIII collisional laser. Results are described for injection into single and double plasma amplifiers. Prismatic lens-like and higher order aberrations in the amplifier are considered. Limitations on ultimate brightness are discussed and also scaling to operation at shorter wavelengths. A preliminary study has been made of UV multiphoton ionization using 300 fs pulses at high intensity.

Research on X-ray lasers at Max Planck Institute of Quantum Optics is reviewed. The main part of this work is performed using the Asterix IV high- power iodine laser, an installation capable of delivering a maximal output energy of 1.2 kJ for a pulse duration of 450 ps. The research areas investigated include photo-resonant pumping, charge transfer X-ray lasers and recombination lasers.

Much progress has been made recently in characterizing the emission from neon- like Yttrium exploding foil x-ray lasers. Concomitant with that effort, we have carried out detailed modeling to enhance our understanding of the experiments and improve their design. Our modeling includes target hydrodynamics, calculation of gain, and both ray and wave optics propagation. We will describe our modeling of Yt x-ray lasers, including first simulations using a two transverse dimensional gain calculation. Our calculations indicate that the time-integrated signal is very sensitive to the time history of the gain, because of the rapid sweep of the beam in angle measured with respect to the plane of the foil.

A calculational theoretical model of the recombination X-ray lasers has been developed describing the level population kinetics in an active medium. A comparison with the experiment shows that it describes correctly the main physical processes in such a laser. A scheme for calculating the angular spectrum of pulsed laser radiation is given and it is shown that it can be utilized for the description of experimental results.

A theoretical basis of ASE action in collisional excitation slab lasers is described. Good agreement with experiment for the germanium laser is obtained, and reasonable agreement with limited data for yttrium. It is found that the gain on the 0-1 transition is only accounted for if the collision rate to its upper state is reduced by a factor 1/2 over the predicted value.

The efficient generation, by a fast discharge, of capillary plasma channels containing Ne-like and Ni-like ions for collisionally excited soft-x-ray lasers is reported. Rapid pulse excitation of capillary channels 1.5 mm in diameter with currents of less than 70 kA produced Ca and Ti plasmas in which atoms are ionized up to the F-like state. Line emission at the wavelengths corresponding to the 3p - 3s and 3d - 3p transitions of Ne-like Ca has been observed.

We present recent results on the development of a small scale soft X-ray laser with low pumping laser energy using a multi-fin target in a two-target chamber. With only 4 J (2 ns) laser beam energy a maximum gain of 7.1 cm^-1 was measured for the CVI 18.2 nm line for a single 6 mm long target. Similar gain (6.5 cm^-1) was also measured for the CVI 13.5 nm line. Control of the gain region in the plasma was demonstrated by changing the influx of iron into the plasma. We also present results from our attempt to generate gain on the 2-1 transition in LiIII at 13.5 nm using a powerful sub-picosecond KrF laser system following work by the RIKEN (Japan) group.

Intensity versus length experiments showed some exponentiation in Ni-like Nb at 204 angstroms, at pump energies of 1 to 2 Joules per pulse of 1 (mu) pump radiation. The largest total gain observed in these experiments is about (alpha) L approximately equals 3 as determined by a Linford fit. Streak camera results indicate that emission at 204 angstroms can persist for u to a nanosecond. More recent experiments indicate that the pump pulse width was variable during this campaign, and that the pump energy calibration was imprecise. Ni-like Nb appears to require on the order of 10¹³ watts/cm² to drive gain, and we plan to increase our ump intensity to improve total gain.

In this paper we report results of a model of a fast capillary discharge (FCD) and discuss them in comparison with experiments. The overall good coincidence between theory and experiment and the observation of stable reproducible compression are beneficial properties of FCD which open the possibility for achieving X-ray laser action in a compact discharge device. The required discharge parameters for lasing in different atomic elements have been calculated.

Laser energy requirements for the creation of active plasma media with Ne- and Ni-like ions with a `long' subnanosecond prepulse (100 - 1000 ps) and a `short' picosecond main pulse (0.1 - 10 ps) have been determined for foil and low density targets (foams, gases, vapors, etc.). RADEX hydrodynamics and atomic kinetics calculations show that X-ray laser action in the 200 - 400 A can be obtained with 1 - 2 J in 100 - 1000 ps prepulse followed of an approximately 1 ps pulse of similar energy. Transient gains of approximately 100 cm^-1 level have been calculated. For the wavelengths 38 - 46 A (`red' edge of `water window' spectral band) a short pulse of only approximately 5 - 10 J is required.

Using Saturn as a driver, we are pursuing both photoresonantly pumped and photoionization/recombination lasers. Our lasing targets are gas cells with thin windows that are pumped by a z pinch 2 cm away radiating 10 TW. In both schemes the lasant and gas fill is neon. We will present evidence for inversion in the sodium/neon photoresonant scheme but we have yet to detect the lasing transition itself. To increase our chances of measuring this line we have introduced potassium into a sodium z-pinch and have eliminated oxygen from the gas cell windows.

We will present results which show lasing on the 3p yields 3s (J equals 0 yields 1) transition in neon-like chromium (Z equals 24), iron (Z equals 24), iron (Z equals 26), and nickel (Z equals 28) at 285, 255, and 231 angstroms respectively. This destroys the myth of titanium being unique and makes highly unlikely that the previously mentioned photo-pumping mechanism is playing a significant role in the titanium laser. The chromium, iron, and nickel experiments all require a prepulse in order to lase and our calculations suggest that the prepulse is an exciting new way to create a uniform low density plasma when illuminating a thick slab target. This allows the proper conditions for gain and laser propagation for low Z neon-like ions and may also be applicable to other systems such as low Z nickel-like ions. We also will present experiments done on other low-Z materials and offer an explanation as to how the hyperfine effect is destroying the gain of neon-like ions with odd Z.

Experimental and theoretical investigations of `self-pumped' photo-resonant X- ray lasers are reported. In these lasers the same kind of ion is used as active medium and for excitation. Simulations of the realization of this idea in a transient X-ray laser and first experiments towards demonstrating a quasi-cw self-pumped X-ray laser are reported.

The high brightness and short pulse duration of soft x-ray lasers provide unique advantages for novel applications. Imaging of biological specimens using x-ray lasers has been demonstrated by several groups. Other applications to fields such as chemistry, material science, plasma diagnostics, and lithography are beginning to emerge. We review the current status of soft x- ray lasers from the perspective of applications, and present an overview of the applications currently being developed.

Collisionally pumped soft x-ray lasers now operate over a wavelength range extending from 35 - 300 angstroms. These sources have high peak brightness and are now being utilized for x-ray imaging and plasma interferometry. In this paper we will describe our efforts to probe long scalelength plasmas using Moire deflectometry and soft x-ray imaging. The progress in the development of short pulse x-ray lasers using a double pulse irradiation technique which incorporates a travelling wave pump will also be presented.

Many applications in material science, chemistry, and atomic physics require an x-ray source that has a repetition ate of 1 Hz to a few kHz. In these fields, a very wide range of photon energies is of interest. One application is time-resolved surface photoelectron spectroscopy and microscopy where low energy (< 1 (mu) J) pulses are required to avoid space charge effects but high-repetition rates (approximately equals 1 kHz) provide the high average power which is needed to obtain the desired resolution. In pump-probe experiments, it is desirable to have the repetition rate of the x-ray source be comparable to the repetition rate of the corresponding IR, optical, or UV laser. We show that the very high-repetition rate of synchrotrons (1 - 1000 MHz) results in an inefficient use of x rays for these types of experiments and that a kHz repetition rate x-ray laser would be an excellent source for many experiments.

We will present experimental and theoretical characterizations of germanium line-focused and stripe x-ray lasers (XRLs). Key experimental parameters we will study include images of emission profiles of the laser blow-off, angular divergences, XRL output intensities, and ionization balances as we vary XRL designs. We will compare the experimental results with 2D laser deposition and hydrodynamics simulations using LASNEX, and study the changes in ionization balances and level populations from post-processing LASNEX results.

Ne-like Se X-ray laser experiments have been performed to examine the effects in line focus width narrowing on amplification in a collisional excitation scheme. Variation from 40 micrometers up to 180 micrometers has been investigated. Significant changes in temperature and ionization balance have been observed and explained from theoretical considerations.

The high throughput soft X-ray optical system was designed, constructed and tested for obtaining of magnified images of nonradiating objects at wavelength (lambda) equals 175...200 angstroms. The optical system consists of normal incidence multilayer mirrors including condenser and Schwarzschild objective with 10^X magnification and it was applied together with laser produced plasma as an X-ray source. The magnified images with 0.7 micrometers resolution were produced in one shot exposure at 0.8...1 J of incident laser energy. These results show the potential for development of table-top soft X-ray microscopes with 1 nanosecond exposure and submicron spatial resolution.

Problems of short period multilayer mirrors fabrication are discussed. Results of synthesis of multilayer structures with nanometer period are presented. The shortest period observed is 13 angstroms for W - Si and W - B₄C sputtered multilayers. Measurements of near normal incidence reflectivity at (lambda) equals 31 - 32 angstroms are described for W - Sc multilayers with period about 16 angstroms. Measured reflectivity achieves 3.3% and is in good agreement with theoretical model.

A number of high-performance normal-incidence multilayer mirrors (MMs) have been fabricated on concave (r equals 1.6 - 2.0 m) fused silica substrates using laser deposition and a magnetron ion sputtering source. The resonance wavelengths (lambda) ₀ equals 2nd of the MMs synthesized are proximate to 45, 130, 175, 190, and 304 angstroms. The MMs have been subjected to scrutiny by a spectroscopic technique employing a laser-plasma broadband XUV radiation source. The spectral shapes of the resonance reflection curves, the (lambda) ₀ values, and the aperture uniformity (topography) of the mirrors have been determined spectroscopically. Normal-incidence reflection maxima, which correspond to higher-order reflection (k(lambda) equals 2n_(lambda )d, k > 1), have been observed for all of the Mo-Si MMs with (lambda) >= 175 angstroms.

A novel diffraction spectroscopic instrument comprising two focusing multilayer mirrors (MMs) at near-normal incidence and a conventional blazed plane grating at grazing incidence has been implemented. A nearly perfect stigmatism and a theoretical resolving power above 6 X 10⁴ are due to the separation of the focusing and dispersing functions. For higher throughput, MMs with nearly identical resonance reflection curves around (lambda) ₀ approximately equals 135 angstroms have been synthesized employing a magnetron ion sputtering source. The instrument performance has been assessed using a laser-plasma XUV radiation source. The spectral resolution in excess of 4 X 10³ and the applicability to space-resolved spectroscopy and plasma diagnosis have been demonstrated.

Stark line broadening for the n equals 5,4 to n equals 3 transitions of Li-like Al and for the n equals 5 to n equals 4 transitions of Li-like Mo and Na-like Rh in multicharged ion plasmas is considered. Line profiles are calculated with the quasi-static approximation for plasma ion broadening and the impact approximation for the electron broadening. The dependence of the linewidth of the Al XI 5f - 3d line on plasma temperature and density is investigated in the electron density and temperature domains typical for the conditions of recombination X-ray laser experiments. Calculated widths of the 5f - 3d line and the profiles of the Al XI 4f - 3d line are compared with experimental and other theoretical data. Tangible effect of Stark line broadening due to plasma ions for the 5g - 4f and 5f - 4d transitions of Li-like Mo and Na-like Rh is demonstrated at plasma conditions reasonable for theoretical investigation of a potential resonantly-photopumped X-ray laser schemes utilizing these transitions.

Laser pulses with high intensity (up to 10¹⁸ W/cm²) and short duration (100 fs) were focused on gases and solids. The result was ionized material, and emission of short pulse x-rays and unicycle electromagnetic pulses with subpicosecond duration.

The interaction of an intense subpicosecond laser pulse with a planar aluminum target is investigated to determine the characteristics of the evolving plasma. In particular, attention is focused on the emitted x-ray pulse, its spectra including K_(alpha ) emission, and intensity. The interaction is simulated with a non-LTE radiation hydrodynamics model self-consistently coupled to a Helmholtz wave equation describing the absorption of S- and P- polarized incident laser radiation. A fraction of the absorbed laser energy is redistributed and expended in fast electrons, which are transported and deposit their energy producing local heating, inner-shell atomic vacancies and K_(alpha ) radiation. The feasibility of creating conditions conducive to the formation of atomic population inversions leading to gain in selected K- and L-shell transitions is explored.

The experimental application of a scheme for travelling-wave excitation along a line focus to x-ray laser development is reported. The scheme utilizes an appropriately stepped prism or mirror inserted into the beam ahead of the focussing optics. It can be used for pulsed excitation down to about 1 ps. X- ray emission travelling with the velocity of light along a line focus is observed in an experiment using 500 fs to 1 ps KrF laser pulses.

Energy level populations and spectral line intensities in plasmas are studied using an advanced uniform approach for the calculation of ion energy levels and elementary processes rate coefficients in plasmas. The spectrum of Ne-like argon for the uniform steady-state plasma is calculated for a wide variation of electron temperature and density. Hence the most efficient lasing at 5 3p - 3s transitions with wavelengths 697.6, 860.6, 727.5, 725.7, 670.7 angstroms should be expected at 10¹⁹ < n_e < 10²⁰ cm^-3 and T_e approximately 60 eV. It is shown that at electron densities of 10¹⁵ < n_e < 10²¹ cm^-3 ratios of the strongest 3p - 3s line intensities are sensitive to electron density; their dependence on electron temperature is much less pronounced.

As z-pinches are powerful sources of X-radiation, the present work treats the possibility of their stratification by a standing light wave with the purpose of regularizing the radiation process. The ponderomotive force push out the plasma from the antinodes of the standing wave. Once the pinch shell has decreased up to the transverse dimensions of the laser beam, further compression takes place only in the wave nodes because of the unbalanced magnetic pressure. Since the temperature (and the pressure) in the plasma remain constant all along the pulse length, in the wave antinodes the process of the plasma ejection in radial direction begins. The resulting linear structure of the hot points of the plasma can be used as a spatial radiator and X-ray undulator.

The possible parameters of the X-ray Free-Proton Lasers (FPLs) based on the high energy storage rings like SSC and LHC are discussed. FPLs programs at the storage rings can start in a parasitic mode like the programs of the first generation of the Synchrotron Radiation sources at the electron synchrotrons and storage rings. Dedicated FPLs based on the storage rings on the energy approximately 50 TeV and more could become the unprecedented monochromatic continuously tunable powerful sources of the hard radiation.