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We present optimization of laser plasma x-ray experimental conditions for ultrafast x-ray absorption spectroscopy measurements on broad range of transition metal oxides. First, the x-ray flux generated from a laser plasma source was optimized with an emphasis on the Bremsstrahlung by investigating the influence of the angle of the incidence of laser beam on a Cu tape target. The x-ray flux emitted in both the front and transmitted side of the target was found to be optimal at the incident angle of 15 ~ 25 degrees. Moreover the manipulation of the Bremsstrahlung peak energy by the laser focus distribution was discussed. In addition to the source optimization, we present a scheme to find the time-delay zero position in a pump-probe experiment together with a normalization scheme for x-ray source fluctuations. As a feasibility check, we present the transmitted spectra of two materials, Ni and NiO.

In this paper the route towards the current optimum of laser generated ion beams by subsequently changing the important parameters such as target thickness, laser pulse contrast, angle of incidence and laser pulse polarization is sketched. Beginning with parameters of isothermal target normal sheath acceleration (TNSA), we reached the regime where the plasma expansion can be described adiabatically and results in a symmetric ion acceleration. Further we demonstrated a way to phase match the accelerating electron population with the ions, namely coherent acceleration of ions by laser pulses (CAIL), which finally lead to radiation pressure acceleration (RPA) if the laser polarization was changed from linear to circular. These findings of ion acceleration with transparent solid targets are additionally supported by analyzing the optical properties of the transmitted laser pulse (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

New perspectives have been opened up in the field of laser–matter interactions due to recent advances in laser technology, leading to laser systems of high contrast and extreme intensity values, where the frontier of maximum intensity is pushed now to about 1022 W/cm2. Many striking phenomena such as laser-acceleration of electrons up to the GeV level, fast moving ions with kinetic energies of several 10s of MeV, as well as nuclear physics experiments have already actuated a broad variety of theoretical as well as experimental studies. Also highly relativistic effects like laser induced electron-positron pair production are under discussion. All these activities have considerably stimulated the progress in understanding the underlying physical processes and possible applications. This article reviews recent advances in the experimental techniques as well as the associated plasma dynamics studies at relativistic intensities performed at the Max-Born-Institute (MBI). Interactions of a laser pulse at intensities above 1019 W/cm2 with water- and heavy-water droplets, as well as, with thin foils are discussed. Rear and front side acceleration mechanisms, particle dynamics inside the dense target, proton source characteristics, strong modulations in proton and deuteron emission spectra, and finally generation of quasi-monoenergetic deuteron bursts are the topics covered in the article.

Intense and stable laser operation with Ni-like Zr and Ag was demonstrated at pump energies between 2 J and 5 J energy from the PHELIX pre-amplifier section. A novel single mirror focusing scheme for the TCE x-ray laser (XRL) has been successfully implemented by the LIXAM/MBI/GSI collaboration under different pump geometries. This shows potential for an extension to shorter XRL wavelength. Generation of high quality XRL beams for XRL spectroscopy of highly charged ions is an important issue within the scientific program of PHELIX. Long range perspective is the study of nuclear properties of radioactive isotopes within the FAIR project.

Highly energetic negative ions have been observed by irradiating water and heavy water micro droplets with ultrashort (35 fs) and highly intense ((0.8–1.2) × 1019 W cm−2) laser pulses. The creation of negative hydrogen (H−), deuterium (D−) as well as oxygen (O−) ions is suggested due to a process in which first their formation takes place in the hot plasma followed by an acceleration together with the positive ions. The negative ions are pulled by the energetic positive ions and propagate with them contributing to the quasineutrality of the beam. The observed phenomenon is discussed on the basis of possible formation and acceleration mechanisms of negative ions.

Propagation of a high intensity (∼1019 W/cm2) ultrashort (∼35 fs) laser pulse through a cloud of water spheres (150 nm diameter) results in hot electron driven proton acceleration up to 1 MeV. It is suggested that during the propagation of the short pulse through the low density wing of the cloud, the leading pulse pedestal is reduced owing to absorption by the preplasma created. Then, the high-intensity peak of the pulse propagates through this underdense plasma and interacts with the high-density inner part of the cloud, which has not been transformed into an underdense plasma so that a sheath acceleration process at each individual microsphere can take place. The observed proton spectra show strong modulations, which are interpreted within the framework of a known fluid-expansion model incorporating two hot-electron populations with significantly different densities and temperatures.

Structured proton spectra and a two-temperature electron distribution were simulated using a 1D3V particle-in-cell code for a plasma created by 35-fs laser pulses with an intensity of I≥1019 W/cm2. Such a two-temperature electron distribution was used as a prerequisite for a fluid dynamical model allowing us to describe the experimentally measured deep dips in the proton energy spectra of laser-produced plasmas from water-droplet targets.

We studied extreme ultraviolet (EUV) emission from Xe cluster jet targets irradiated with high repetitive ps and ns laser pulses in the intensity range between 10(11) and 10(15) W/cm(2). It was fou ...

A simple model of dynamics of a collisional X-ray laser is given applying Maxwell-Bloch equations in a uniform approximation. The main considered parameters include polarization and coherence of the emitted radiation. Speckle pattern, typical for a radiation source of partial coherence, especially, if involving process of the amplified spontaneous emission (ASE), are used as an alternative source of information on the processes occurring in the active medium of an X-ray laser. A level of partial coherence is deduced by statistical analysis of the speckle pattern generated in the output beam of the laser. It is shown that plasma fluctuation and non-Gaussian character of the statistics are needed to reproduce the transverse coherence values reported in the experiment.

If regions of localized strong fields at plasma-vacuum interfaces are probed longitudinally with laser accelerated proton beams their velocity distribution changes sensitively and very fast. Its measured variations provide indirectly a higher temporal resolution as deduced from deflection geometries which rely on the explicit temporal resolution of the proton beam at the position of the object to probe. With help of reasonable models and comparative measurements changes of proton velocity can trace the field dynamics even at femtosecond time scale. In longitudinal probing, the very low longitudinal emittance together with a broad band kinetic energy distribution of laser accelerated protons is the essential prerequisite of the method. With a combination of energy and one-dimensional spatial resolution, we resolve fast field changes down to 100 fs. The used pump probe setup extends previous schemes and allows discriminating simultaneously between electric and magnetic fields in their temporal evolution.

The satellite structure accompanying the Al Lyα emission from plasma regions close to the surface of the laser-irradiated targets is studied. In spectra produced at constant laser energy but variable pulse duration we identify the situations where the resonance line is suppressed and only the emission from long-wavelength satellites is observed. The experimental data are compared with results of calculations based on two-dimensional hydrodynamics and multilevel collisional-radiative codes. Simulations indicate that these spectra originate from cold dense plasma created inside the crater several tens of micrometers under the surface of the solid target.

We describe an experiment demonstrating XUV amplification following collisional excitation in a discharge-created plasma waveguide irradiated by a picosecond optical laser pulse. A capillary discharge was used to generate a plasma radiation pipe with a radially concave electron density profile. Temporally resolved transmission characteristics and guiding effect have been measured. An intense short laser pulse rapidly heated the electrons, producing amplification in the 3p 1 S 0 -3s 1 P 1 transition of Ne-like S at 60.84 nm. The integrated gain-length product obtained within a 3 cm active medium with a laser energy of 0.46 J was -6.8. The pump energy depletion has been analysed as well. This new, hybridly pumped soft X-ray laser with the transient gain offers a new way towards efficient tabletop coherent XUV sources.

Results from particle-in-cell simulations of the three-dimensional regime of proton acceleration in the interaction of laser radiation with a thin spherical target are presented. It is shown that the density of accelerated protons can be several times higher than that in conventional accelerators. The focusing of fast protons created in the interaction of laser radiation with a spherical target is demonstrated. The focal spot of fast protons is localized near the center of the sphere. The conversion efficiency of laser energy into fast ion energy attains 5%. The acceleration mechanism is analyzed and the electron and proton energy spectra are obtained.

For laser plasma diagnostic purposes, a specific Thomson spectrometer with a multi-pinhole array at the entrance aperture is proposed. The ion beam under investigation is thus divided into small beamlets and the obtained spectral image combines the recorded spectra of the ions, which are emitted under different angles of the source. This resembles a simultaneous measurement with many independent spectrometers. Thereby, the emission characteristic of the ion source can be reconstructed. The quantitative analysis of the ion emission spectra allows one to gain detailed information about the accelerating sheath field profile and dynamics.

We describe an experiment demonstrating XUV amplification following collisional excitation in a capillary discharge plasma irradiated by a picosecond IR laser pulse. Guiding and temporally resolved transmission of the pump laser beam are also demonstrated and analysed. The short pump laser pulse heated rapidly the electrons producing amplification in the 3 p 1 S 0 –3 s 1 P 1 transition of Ne-like sulphur at 60.84 nm. The estimated gain–length product was equal to 6.8, while the beam divergence reached 2.5 mrad for 30 mm capillary. This new, hybridly pumped collisional soft X-ray laser with the transient gain offers a new way towards efficient table-top XUV sources.

Simulations are presented for the collisionally pumped germanium X-ray laser working in the transient gain scheme. The influence of the shape, length, intensity and energy of the preforming pulse on the gain and X-ray output are analysed. The hydrodynamics simulations post-processed with 3D raytracing give additional information about the effective gain and the output signals determined by the refraction due to the plasma density gradients. The modelling presented shows to what extent the plasma preforming plays a deciding role for the improvement of the lasing conditions. Dependence on the main pulse delay is tested as well. There are indications that significant gain and output signal could be created with a subpicosecond main driving pulse of reduced total energy provided the preforming pulse is optimised.

Information about the energy distribution of hot electrons generated by the interaction of short-pulse (0.7 ps pulse duration at laser wavelength) and high-intensity laser beams with solid targets is derived from measurements of the spectral and angular distribution of hard x-rays with energies above 10 keV. The measurements were carried out with thermoluminescence dosemeters and a nine-channel spectrometer. A comparison of experimental data and model calculations shows that under the conditions of our experiment the hot-electron distribution deviates significantly from a Maxwell - Boltzmann shape with a single-electron temperature parameter.

Lasing in a titanium XII plasma at 32.6 nm and ∼ 30 nm as well as in vanadium XIII at 30.4 nm using a short pulse driven transient inversion population has been realized. Gain performances and temporal characteristics of the X-ray signal output at only few Joules of pump energy are described.

A novel two-step excitation scheme for an efficient table-top x-ray laser has been realized for the first time. A nanosecond pulse creates a plasma of neonlike ions of titanium, followed by a subpicosecond pulse which excites a nonstationary population inversion. With only a few joules of pump energy, a compact x-ray laser at 32.6 nm with a very high gain coefficient of $g\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}19{\mathrm{cm}}^{\ensuremath{-}1}$ and a gain-length product of $gL\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}9.5$ was achieved.

Calibrated thermoluminescence dosimeters have been used to measure the angular and spectral dependence of hard x‐ray emission produced from intense subpicosecond laser irradiation of solid targets. A dosimeter detector set with nine filter channels (13.5–400 keV) has been tested successfully. Total bremsstrahlung conversion up to 0.23% and conversion of 8×10−5 from laser energy to Ta Kα line emission (photon energy ≊57 keV) was determined. The scaling of the hard x‐ray yield with laser intensities ranging from 3×1016 to 3×1018 W/cm2 was investigated.

New excitation channels for the explanation of the strong emission of Li-like and Be-like satellite transitions in numerous picosecond and subpicosecond laser-produced plasma experiments are proposed. `Blue Li-like satellites' of the He-like resonance line W are predicted. Corresponding spectral simulations exploiting new calculated atomic data for these mechanisms are in rather good agreement with experimental single-shot spectra of plasma produced at the intensities up to and recorded by means of a high-resolution spherically bent mica crystal technique.

Hard x‐ray emission in the range of 100 keV has been measured from plasmas produced by irradiation of solid targets with ps laser pulses up to 7×1017 W/cm2. The experimental data obtained for oblique incidence of p‐polarized laser light at different illumination angles are compared to computer calculations, which include the processes of resonance absorption and vacuum heating. The scaling of hard x‐ray emission with varying laser flux is consistent with the theoretical model of bremsstrahlung emission of hot electrons. From this, together with an absolute radiation dose measured with calibrated detectors, a transfer of up to 50% of the incident laser energy to suprathermal (∼10...100 keV) electrons is estimated.

A 1.5 picosecond laser pulse with an intensity of more than 1018 W/cm2 was used to heat solid state magnesium targets. The unique characteristics of this plasma source together with a high resolution recording system ( λ Δλ = 10 4 ) allowed us to study multicharged ions with L- and M-shell dielectronic satellite structures in the wavelength range of 9.2–9.5 A. Ten spectral lines determined by 1s2p4l–1s24l and 1s2p3l–1s23l transitions in Mg X and of 43 spectral lines of Mg IX were identified and measured. Parameters of the plasma in the process of its evolution were deduced.

The interaction of 2 ps FWHM laser pulses with solid targets at intensities ${10}^{16}$-${10}^{18}$ W/${\mathrm{cm}}^{2}$ is studied for two essentially different cases of laser front steepness resulting in preplasma and preplasma-free interaction. Red and blue frequency shifts of a backscattered fundamental wave and its second harmonic depending on the incident laser pulse shape are observed. They are associated with Doppler shifts corresponding to inward or outward movement of the critical density surface. A model including ponderomotive force was developed to explain the experimental results.

The x-ray emission spectrum of a magnesium plasma produced by a picosecond laser has been studied. Dielectronic satellites of the resonance line of the He-like Mg XI ion have been identified for the first time. These satellites result from radiative transitions from 1s2l2l'3l'' autoionizing levels of the Be-like Mg IX ion.

The properties of a magnesium plasma heated by picosecond laser pulses have been determined by x-ray spectral methods. Experiments were carried out at a laser power density ~ 1.5 1018 W/cm2. The x-ray spectra were detected by spectrographs with a plane CsAP crystal and a mica crystal bent into part of a spherical surface 10 cm in radius. The experimental data are compared with predictions of a calculation on the time-varying kinetics of multiply charged magnesium ions.

It has been shown experimentally that a source based on a plasma produced by a picosecond laser is extremely promising for systematic research on the satellite structures of multiply charged ions which have electrons in L or M shells. The combination of the unique characteristics of this source and the particular measurement apparatus used (with a spectral resolution Δλ/λ~10−4) has made it possible to refine the wavelengths of several transitions of Mg IX and X ions which had been identified previously, to identify for the first time ten spectral lines due to 1s2p4l → 1s24l and 1s2p3l → 1s23l transitions of the Mg X ion, and to measure the wavelengths of 47 spectral lines which have tentatively been attributed to the Be-like ion Mg IX.

Spatially resolved x-ray spectra of the Al Lyman α group emitted from the surface of the laser- irradiated targets display plasma regions where the resonance line is suppressed and the dielectronic satellites dominate. Calculations based on multilevel collisional-radiative code and two-dimensional hydrodynamic simulations relate this spectral distribution to a presence of the cold overcritical density plasma inside the crater at the target surface.

Laser-driven acceleration of particle beams is a burgeoning field of research, based on the possibility of creating ultra-large electric fields in plasma, largely exceeding current limits of conventional acceleration technology. Research in this area has led to very significant progression regarding the acceleration of electrons and ions. Laser-driven ion sources have unique properties: high brightness (about 1013 protons/ions per shot), high current (in kiloAmpere range), ultra-low emittance, and short pulse duration (less than 1 ps), opening prospects for a broad range of applications. Recent advances in the laser technology have led to even further enhancements in the provision of extremely short and high-intensity pulses, which can further improve the accelerated ion beam specifications particularly regarding maximum ion energy and ion flux which are demanding most of the potential applications. These developments have stimulated an emergence of advanced diagnostics for measuring complex plasma effects. The absorption mechanisms of laser radiation at the target are the basic processes, which indeed defines the whole ion acceleration scenario. For laser intensities, where the classical normalized momentum of electrons quivering in the laser electric field: a = 8.53×10−10 (μm) I1/2 (W/cm2) > 1, the electrons become relativistic and the effect of the laser magnetic field is no longer negligible. The perpendicular component of the Lorentz force ev×B couples with the electric force to drive the electrons in the laser propagation direction (Wilks et al., 1992, Lefebvre & Bonnaud, 1997, Kruer & Estabrook, 1985) in contrast to inverse bremsstrahlung and resonance absorption, which causes the quiver motion of the electrons in the laser field. The ponderomotive force drives the electrons with a stepor plateau-like density profile and has a strong directionality along the laser propagation direction. Electron temperatures about 1 MeV have been measured (Malka & Miquel, 1996). The laser energy transfer to the hot electrons can also be out carried by fast plasma waves through the nonlinear ponderomotive force (Tajima & Dawson, 1979) and by laser field itself (Pukhov et al., 1999).

We are reporting on the development of a diode-pumped chirped-pulse-amplification (CPA) laser system based on Yb:YAG thin-disk technology with a repetition rate of 100 Hz and output pulse energy in the joule range. The focus lies with the first results of the preamplifier--a regenerative amplifier (RA) and a multipass amplifier (MP). The system consists of a front end including the CPA stretcher followed by an amplifier chain based on Yb:YAG thin-disk amplifiers and the CPA compressor. It is developed in the frame of our x-ray laser (XRL) program and fulfills all requirements for pumping a plasma-based XRL in grazing incidence pumping geometry. Of course it can also be used for other interesting applications. With the RA pulse energies of more than 165 mJ can be realized. At a repetition rate of 100 Hz a stability of 0.8% (1sigma) over a period of more than 45 min has been measured. The optical-to-optical efficiency is 14%. The following MP amplifier can increase the pulse energy to more than 300 mJ. A nearly bandwidth-limited recompression to less than 2 ps could be demonstrated.

Laser accelerated proton beams have been used for field characterization in expanding plasmas. The Thomson parabola spectrometer, as a charged particles analyzer, also allows precise measurement of the charged particles' trajectories. The proton's deflections by fast changing plasma fields can be measured with the new design of the Thomson parabola spectrometer and, therefore, it can be applied for proton deflectometry. It is shown that from resulting spectrograms the plasma field dynamics can be reconstructed with high temporal resolution. In a proof-of-principle experiment, a weakly relativistic plasma expansion is studied as an example.

The present trends in the development work on X-ray lasers are shown and discussed on a background of a brief history of the collisionally pumped X-ray lasers. The presentation is focused on two variants of the transient inversion pump method succesfully applied in the experiments - slab target geometry and single profiled laser pulse. Recently, another scheme referred to as GRIP (GRazing Incidence Pumping) has been proposed and demonstrated. This pump geometry opens the new real possibility to construct a repetitive X-ray laser. Some aspects of tile pump scheme implementation are discussed in detail. Finally, a specific injector-amplifier system giving a new perspective on the future of X-ray lasers is dicussed briefly as well.

The operation of a Ni-like Mo x-ray laser at 18.9 nm with a repetition rate of 10 Hz has been demonstrated. The laser has been pumped applying the grazing incidence pump arrangement, where a short (picoseconds) pulse irradiates a Mo plasma column generated by a long (a few hundred picoseconds) pulse. The delayed short pulse is incident at a grazing angle on the plasma to heat it efficiently. We used a total energy of less than 450 mJ ( 150 mJ in the long and 250-300 mJ in the short pulse) in a line focus of 7 mm by 50 microm .

Some prospects for development of collisional X-ray lasers with a high repetition rate based on the output characteristics of a transient Ni-like Ag soft X-ray laser pumped by a single picosecond laser pulse are analysed. Such problems as target technology, new driver development and the active medium parameters are discussed.

We discuss progress in numerical and experimental research of table-top X-ray lasers based on several schemes that have emerged successfully in recent years. We discuss the progress, trends and major differences of modern approaches in X-ray laser design to previous efforts. The efficiency issues and main properties of X-ray lasers based on laser-produced and electrical discharge-created plasmas that have made this improvement possible will be outlined.

Particle-in-cell simulations of the absorption of an ultrashort and ultraintense laser pulse at structured targets are presented. The targets consist of a bunch of parallel or tapered carbon nanowires. Such targets are effective in generating large currents of relativistic electrons, propagating along the wires and following their curvature. Focusing the electron beam into one wire makes it possible to reduce the transverse size of the electron cloud in comparison to the diameter of the laser pulse. The density of the energy flux of the hot electrons in such a bunch, propagating along one nanowire, is in the excess of several times the intensity of the laser pulse.

This paper summarizes our recent progress achieved in the characterization and understanding of the Ni-like Ag transient x-ray laser pumped under traveling wave irradiation. At the Rutherford Laboratory CPA laser facility, we measured the temporal history of the 13.9 nm laser pulse with a high-resolution streak camera. A very short, approximately 2 ps x-ray laser pulse was directly demonstrated for the first time. More recently we carried out an experiment at the LULI CPA laser facility. Several diagnostics that recorded the plasma emission at the XRL wavelength or in the keV range indicate the presence of small-scale spatial structures in the emitting XRL source. Single-shot Fresnel interferograms at 13.9 nm were successfully obtained with a good fringe visibility. Strong lasing was also observed on the Ni-like 4f-4d line at 16 nm.

Analysis of the capillary discharge plasma as a possible preformed active medium of the collisionally pumped soft X-ray lasers (XRLs) working within the transient inversion scheme is presented. Temporal dependence of the plasma column resistance is compared with a 1D-model used in the numerical simulations of the plasma dynamics. Numerical analysis of the laser absorption determines the pump parameter range for efficient excitation of the longitudinally pumped hybrid XRLs.

In this article we describe a laser plasma source for Extreme Ultraviolet Lithography (EUVL) based on a liquid water jet target. Although jet targets are known for some time now, no attempts have been made to prove the functionality of the target under conditions similar to an EUVL production-line facility, that means illumination with high average power laser systems (in the multi-kW regime) at repetition rates in the kHz region. Such systems are currently under development. We used the MBI-burst laser to simulate these extreme illumination conditions. We examined the hydrodynamic stability of the target as a function of the laser repetition rate at different average laser powers (0.6kW and 5kW per burst). Additionally, the dependence of the conversion efficiency on pulse duration in the range from 30ps to 3ns was investigated. From our results one can conclude parameters for future design of driver lasers for EUVL systems.

Summary form only given. The temperature of hot electrons achieved in the dense plasma at moderate intensities of 10/sup 16/-10/sup 17/ W/cm/sup 2/ has been proved to be enough to provide excitation of low energy nuclear stable isomers. Besides promising applications of this process such as quantitative spectroscopy of low energy levels in metastable nuclear isomers, nuclear isotope separation, the ultimate goal of G-lasing using metastable isomers seems feasible. Between different main mechanisms responsible for such excitation - photoexcitation by plasma X-rays, excitation through inelastic electron scattering and inverse internal electronic conversion, the first one has the highest cross section in hot dense femtosecond laser plasma. We discuss the impact of nuclear line broadening in plasma (due to ion-ion collisions, Doppler effect, Zeeman broadening by plasma self-generated magnetic field, Stark broadening, etc.) on the total number of excited nuclear isomers.

Results of measurements on a plasma created by a discharge in a sulfur capillary and irradiated by a picosecond laser pulse are presented. Time-resolved transmission measurements and the corresponding XUV spectra are discussed. It is found that the transmission of the laser through the capillary decreases abruptly after the peak of the discharge current, and that the profile of the output laser beam is symmetrized before the onset of the opaque period. The spectra are evidently affected by the laser pulse and show significant intensification on the 3p-3s transition in Ne-like sulfur at 60.84 nm. This observation, combined with the fact that the emission of this line appears spatially displaced from all other lines in the detector and presents a lower divergence, suggest that lasing is occurring.

For the development of a heavy ion driven inertial confinement fusion scenario a detailed knowledge of the interaction processes of the ions with the converter material is crucial. As this converter will be predominantly in the plasma state one of the main topics of the plasma physics group at Gesellschaft fuer Schwerionenforschung (GSI) is the interaction of heavy ions with dense hot plasma. Based on the latest result on interaction experiments with laser generated plasma targets presented here and concerning the high current upgrade of GSI a new high energy laser system is proposed. It will serve as a driver for interaction experiments with heavy ions as well as a diagnostic tool for heavy ion generated plasmas. In addition, with the combination of high current heavy ion beams and intense lasers innovative, fundamental research in the field of high energy density physics will be accessible for the first time.

Low pump energy transient gain x-ray lasers in Ti at 32.6 nm, 30.15 nm, in V at 30.4 nm and Ge at 19.6 nm using picosecond pulse heating of a long pulse preformed plasma of neonlike ions has been realized for the first time. Gain saturation was demonstrated in Ti and Ge XRL. Results of pump consumption, x- ray divergence and output energy are given.

Numerical modeling of transient inversion and capillary discharge x-ray lasers were performed for the purposes of understanding of recent experiments, improving the laser efficiency and planing their further development. The first demonstration of saturation of a low pump energy x-ray laser utilizing a transient inversion mechanism on the 3p - 3s transition at 32.63 nm in Ne-like Ti has been confirmed. A close to saturation amplification was simultaneously achieved for the 3d - 3p, J equals 1 - 1 transition at 30.15 nm. Small signal effective transient gain coefficients of g approximately equals 46 cm-1 and approximately 35 cm-1 and effective gain-length products of 16.7 and 16.9 for these lines were obtained. Experiments and calculations demonstrate that it is possible to achieve saturated laser action in a transient regime with Ne-like Ti for a pump energy as low as approximately 5 J. With such energies just recently the lasing on Ni-like Pd at 14.7 nm has been achieved. MHD simulations of capillary discharges were performed for several elements with shorter lasing wavelengths. A new approach which intends to combine advantages of electrical discharge plasma preparation with CPA-laser excitation was investigated. It will enable a kind of x-ray lasers to be built with ultrashort pulse duration and the high efficiency. In this case the well preformed cylindrical shell of discharge plasma and the transient population inversion combined with the traveling-wave excitation will enable to achieve lasing at much shorter wavelengths.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present observations of intense beams of energetic negative hydrogen ions and fast neutral hydrogen atoms in intense (5 × 1019 W/cm2) laser plasma interaction experiments, which were quantified in numerical calculations. Generation of negative ions and neutral atoms is ascribed to the processes of electron capture and loss by a laser accelerated positive ion in the collisions with a cloud of droplets. A comparison with a numerical model of charge exchange processes provides information on the cross section of the electron capture in the high energy domain.

The scenario of “electron capture and loss” has been recently proposed for the formation of negative ion and neutral atom beams with up to MeV kinetic energy [S. Ter-Avetisyan, et al., Appl. Phys. Lett. 99, 051501 (2011)]. Validation of these processes and of their generic nature is here provided in experiments where the ion source and the interaction medium have been spatially separated. Fast positive ions accelerated from a laser plasma source are sent through a cold spray where their charge is changed. Such formed neutral atom or negative ion has nearly the same momentum as the original positive ion. Experiments are released for protons, carbon, and oxygen ions and corresponding beams of negative ions and neutral atoms have been obtained. The electron capture and loss phenomenon is confirmed to be the origin of the negative ion and neutral atom beams. The equilibrium ratios of different charge components and cross sections have been measured. Our method is general and allows the creation of beams of neutral atoms and negative ions for different species which inherit the characteristics of the positive ion source.

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.

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.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

X-ray emission and laser absorption have been studied with pulses of 1.5 ps duration irradiating solid targets at intensities of 1018 W/cm2. Absorption as a function of the incident laser flux and the irradiation angle in respect to the polarization reaches maximal values of 50% and is discussed in comparison to theoretical works published recently. This gives basic guidelines for efficient x-ray production which we have investigated in the hard (Ex > 50 keV, Bremsstrahlung) and soft (Ex < 1 keV, line emission of ions) spectral region. The feasibility of a short pulse and a plasma source with an extension of only some microns is proofed with an experiment using a spherically bent Mica crystal for collimation of the x-ray beam. The brightness and divergence of that x-ray beam being relevant for applications are given.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.