This paper reports on a novel approach for producing high energy femtosecond pulses without external amplification. The so-called chirped-pulse oscillator (CPO) concept is based on an extended-cavity oscillator, operating at small net positive intracavity group delay dispersion (GDD), over a broad spectral range by the use of chirped multilayer mirrors. The resultant chirped picosecond pulses are compressed by a dispersive delay line external to the laser cavity. Utilizing this technique, sub-30 fs pulses with an energy exceeding 200 nJ at a repetition rate of 11 MHz were produced. The demonstrated peak power in excess of 5 MW is the highest ever achieved from a cw-pumped laser and is expected to be scaleable to tens of megawatts by increasing the pump power and/or decreasing the repetition rate. The demonstrated source allows micromachining of any materials under relaxed focusing conditions.

This paper summarizes experimental results on the injection and transport of intense, wide cross-section H+ plasma (PB), and ion beams (IB), in vacuum and ambient H+ plasma across an applied B-field. The injection of plasma and ion beams into magnetic confinement devices have the potential to heat and support current in these systems (e.g., field-reversed configurations). The translational energies of the PB and IB ranged between Epb = 60 to 120 eV and EIB = 60 to 120 keV, with temperatures and densities in the range of Tb ∼ 2 to 10 eV, nb ∼ 1012 to 1013 cm−3, and Tb ∼ 200 eV, nb 1010 to 1011 cm−3, respectively. Compared to earlier studies (Peter et al., 1979; Wessel et al., 1988, 1990), this research extends the experimental parameter space to higher beam current densities (up to 30 A/cm2) and higher B-field strengths up to 1.6 kG. The PB and IB were both about 10 cm in diameter at the injection port, and the ratio of beam specific energy to ambient B-field specific energy, β, was in the range of 0.1 to 10. Ratios of beam Larmor radius to beam size, ρ, ranged from 10−1 to 1 and 1 to 10 for the PB and IB, respectively. Cross B-field propagation of the PB in vacuum was undeflected as a whole with a sharp increase (one order or more) in the current density of the central beam core at B-field levels > 1 kG accompanied by a significant loss of beam peripheral layers, beam “braking” and preferential beam expansion along the B-field lines. Cross B-field propagation of the PB in ambient plasma did not differ substantially from the case without B-field, that is, no deflection of the PB as a whole, which could be due to an insufficient neutralization of the induced E-field inside the PB. Cross B-field propagation of the IB in ambient plasma followed a single particle trajectory deflection with a simultaneous significant loss of IB intensity without any detectable bunching, indicating an adequate shorting of the polarization E-field inside the IB.

This paper represents the results of a study of angular distribution of laser produced ions (LPI) of Al, Cu, and Ag. The angular distribution is studied by CR-39 (SSNTD) and ion assisted sputtering experiments. A Q-Switched Nd:YAG laser (1.064 μm, 1.1 MW) with 10 mJ pulsed energy was used to produce the Ag ions, which were detected by CR-39 detector mounted at −17.5°, 0°, 17.5°, 30°, 60°, and 90° from the normal to the target placed at a distance of 9 cm from the target. Etched CR-39 detectors then observed under the Motic DMB Series optical microscope. A bunch of ions was detected along the normal of target due to self generated collimation of ions. This is termed as Forward Peaking of Laser Produced Ions. Similar results were also observed from sputtering of polished Al substrate by laser produced ions of Cu and Sputtering of polished Cu substrate by laser produced ions of Al. The surface morphology of the ion irradiated samples were observed under the Scanning Electron microscope (SEM) S 300 Hi-tech. Formation of a circular damage on the surface of the substrates by irradiation conforms the ions collimation along the normal or Forward Peaking of ions.

The compression of a cryogenic hydrogen cylindrical sample contained in a hollow gold target driven by an intense co-axial uranium beam has been studied. The ion distribution is assumed to be Gaussian in space and parabolic in time. The hydrodynamics of the target is analyzed by means of one- and two-dimensional numerical simulations. A parametric study is performed to achieve the maximum average hydrogen density and temperature as a function of the sample radius, total number of ions and spread of the spatial ion distribution. A window in the beam-target parameters for which hydrogen compression is higher than a factor of 10 and temperature is below 0.2 eV has been found by considering a single bunch that contains 2 × 1011 uranium ions delivered in 100 ns. In this range of high densities and low temperatures, it is expected that hydrogen may become metallic.

The possibilities of producing ultrahigh-current-density ps ion fluxes by the skin-layer interaction of a short (≤ 1ps) laser pulse with plasma were studied using two-fluid hydrodynamic simulations, and the time-of-flight measurements. Backward-emitted ion fluxes from a massive (Au) target as well as forward-emitted fluxes from various thin foil targets irradiated by a 1-ps laser pulse of intensity up to 2 × 1017 W/cm2 were recorded. Both the simulations and the measurements confirmed that using the short-pulse skin-layer interaction of a laser pulse with a thin pre-plasma layer in front of a solid target, a high-density collimated ion flux of extremely high ion current density (∼ 1010 A/cm2 close to the target), can be generated at laser intensity only ∼ 1017 W/cm2. The ion current densities produced by this way were found to be comparable to (or even higher than) those estimated from recent short-pulse experiments using a target normal sheath acceleration mechanism at relativistic laser intensities. The effect of the target structure on the current densities and energies of forward-emitted ions is demonstrated.

The dynamics of the expansion plasma produced by excimer laser ablation of a silicon target into oxygen and mixed O2/Ar atmosphere were studied by means of time-resolved imaging of the expanding plume. Experiments were performed in pure oxygen, ranging between 0.13 and 13.33 Pa, and at different O2/Ar ratios at a fixed total pressure of 13.33 Pa. The occurrence of a shock wave (SW) generated by the supersonic expansion of the plasma was observed at high pressure values. The presence of the SW had a strong influence on the structure of SiOx thin films. In fact, silicon dioxide thin films were always obtained in presence of the SW, irrespective of the oxygen content in the gaseous mixture. On the contrary, suboxide thin films were obtained when the expansion occurred at lower pressure values (no SW presence). The temperature rise following the developing of the SW, is supposed to enhance the oxygen molecules dissociation by increasing the efficiency of the silicon oxidation reaction.

Hydrodynamic instabilities play an important role in the target compression for inertial confinement fusion (ICF). We present the analytical solution of a perturbed isentropic implosion. We compare the analytical solution to the results obtained with perturbation and bi-dimensional Lagrangian hydrodynamic codes. We also compare results from bi-dimensional code and perturbation code on an ICF like test case.

Plasma-based accelerators have been proposed for the next generation of compact accelerators because of the huge electric fields they can support. However, it has been difficult to use them efficiently for applications because they produce poor quality particle beams with large energy spreads. Here, we demonstrate a dramatic enhancement in the quality of electron beams produced in laser-plasma interaction: an ultrashort laser pulse drives a plasma bubble which traps and accelerates plasma electrons to a single energy. This produces an extremely collimated and quasi-monoenergetic electron beam with a high charge of 0.5 nanocoulomb at energy 170 ± 20 MeV.

Experiments on laser ablation of metals in air, in vacuum, and in similar irradiation conditions, revealed that the ablation thresholds in air are up to three times lower than those measured in vacuum. Our analysis shows that this difference is caused by the existence of a long-lived transient non-equilibrium surface state at the solid-vacuum interface. The energy distribution of atoms at the surface is Maxwellian-like but with its high-energy tail truncated at the binding energy. We find that in vacuum the rate of energy transfer from the bulk to the surface layer to build the high-energy tail, which determines the lifetime of this non-equilibrium state, exceeds other characteristic timescales such as the surface cooling time. This prohibits thermal evaporation in vacuum for which the high-energy tail is essential. In air, however, collisions between the gas atoms and the surface markedly reduce the lifetime of this non-equilibrium surface state allowing thermal evaporation to proceed before the surface cools. It was experimentally observed that the difference between the ablation depth in vacuum and that in air disappears at the laser fluencies 2–3 times in excess of the vacuum threshold value. The material removal at this level of the deposited energy density attains the features of the non-equilibrium ablation similar for both cases. We find, therefore, that the threshold in vacuum corresponds to non-equilibrium ablation during the pulse, while thermal evaporation after the pulse is responsible for the lower ablation threshold observed in air. This paper provides direct experimental evidence of how the transient surface effects may strongly affect the onset and rate of a solid-gas phase transition.

The Prague Asterix Laser System (PALS) research program covers a broad spectrum of laser–plasma experiments in the range of power densities of 1014-5 × 1016 W/cm2, aimed at development and applications of laser plasma-based ion and soft X-ray sources of plasma based ultra-bright XUV lasers in particular. In parallel to these two main lines of research, various principal tasks of laser plasma physics are being studied, such as generation and propagation of laser-induced shock waves, laser ablation, and crater creation processes or laser imprint treatment. Results selected of numerous experimental projects performed at PALS within the period 2002–2004 are surveyed in the paper, experiments with intense soft XUV laser beams being highlighted on the first place.

In order to develop a high repetition rate X-ray lasers, the longitudinal-pumped transient collisional excitation (TCE) X-ray laser is one of the most effective pumping schemes. The high directive Ni-like Mo 18.9 nm soft X-ray laser pumped by modest laser energy has already been demonstrated by using the tabletop size Ti:sapphire/Nd:glass laser system that delivering energy of 150 mJ in 475 fs at the center wavelength of 1054 nm. The total energy in the pre-pulse and the main pulse was 150 mJ, which will make possible multi-hertz operation. To pursue the high repetition rate of the laser-driven TCE X-ray laser, we have designed a new 20 TW Ti:Sapphire laser system (600 mJ, 30 fs, 10 Hz). Special attention was paid to improve the contrast ratio, control of pulse shape as well as phase by an acoustic optic programmable dispersive filter (AOPDF) and 1 kHz preamplifier. Preliminary data have shown good laser characteristics. As the preliminary experiments, we have investigated high order harmonics generation from low-density laser plasma by using the solid target irradiated by a femtosecond laser pulse. The highest order was the 51st. harmonic at wavelength of 15.61 nm.

Imploding indirect-drive double shell targets may provide an alternative, non-cryogenic path to ignition at the National Ignition Facility (NIF). Experiments are being pursued at OMEGA to understand the hydrodynamics of these implosions and the possibility of scaling it to the NIF design. We have used 40 beams from the OMEGA laser to directly drive the capsules, and we have used the remaining 20 beams to backlight the imploding shells from two different directions at multiple times. We will review the recent experiments to measure the hydrodynamics of the targets using two-view X-ray radiography of the capsules. We will present data on measured yields from the targets. We will present a measured time history of the hydrodynamics of the implosion. Experiments were pursued using direct drive in which the M-band effect (experienced in the indirect drive experiments) could be eliminated or controlled. It was learned in the direct drive experiments that the best performing capsules were those that had a thin outer layer of gold. This effectively causes M-band pre-heat effects giving implosion hydrodynamics and performance closer to the indirect drive case. We will review the methods used to radiograph the targets and the techniques used to extract useful information to compare with calculations. The effect of imperfections in the target construction will be shown to be minimal during the initial stage of implosion. The yields from the targets were observed to be uniformly low compared to indirect-drive.

Very high plasma densities can be obtained at the end of the implosion phase in inertial fusion targets, particularly in the so-called fast-ignition scheme (Tabak et al., 1994; Mulser & Bauer, 2004), where a central hot spark is not needed at all. By properly tailoring the fuel compression stage, degenerate states can be reached (Azechi et al., 1991; Nakai et al., 1991; McCory, 1998). In that case, most of the relevant energy transfer mechanisms involving electrons are affected (Honrubia & Tikhonchuk, 2004; Bibi & Matte, 2004; Bibi et al., 2004). For instance, bremsstrahlung emission is highly suppressed (Eliezer et al., 2003). In fact, a low ignition-temperature regime appears at very high plasma densities, due to radiation leakage reduction (León et al., 2001). Stopping power and ion-electron coulomb collisions are also changed in this case, which are important mechanisms to trigger ignition by the incoming fast jet, and to launch the fusion wave from the igniting region into the colder, degenerate plasma. All these points are reviewed in this paper. Although degenerate states would not be easy to obtain by target implosion, they present a very interesting upper limit that deserves more attention in order to complete the understanding on the different domains for inertial confinement fusion.

In this work, we first presents a review of the work that research teams have developed in collaboration in order to determine the optical properties of plasmas during the recent years, and showing the achievements reached. The second part of this paper is devoted to one of these improvements, which is to include reabsorption of the radiation in the calculations of dense optically thick plasmas in non-LTE conditions. Two models recently developed for this purpose are presented. The quantitative study was focused on aluminum plasmas, which was obtained recently at LULI experiments.

Laser technology developments, including construction of a 286-TW Ti:Sapphire laser with a focused intensity of 1021W/cm2, installation of the TIL, prototype of the SG-III, and operation of the SG-II laser are presented. Results of the experiments on hohlraum physics, indirect-drive implosion, Thomson scattering, EOS, and X-ray laser are briefly introduced. Simulations and a code package, LARED, for target physics are outlined.

We present in this paper a theoretical modeling and a numerical simulation devoted to the problem of transport and energy deposition profile of high current light ion beams interacting with dense matter. A numerical code, named MBC-ITFIP, is used to follow the trajectories of light atomic or molecular ions inside plasma targets with non-uniform density, temperature and composition profiles. MBC-ITFIP has been more specifically optimized for application of ion beams generated by the new high intensity laser sources, such as radiography and isochoric heating of dense plasmas.

The electromagnetic acceleration of a metallic ring carrying a high current, combined with the mutual interaction of a concentrical conductor carrying the same current, in the presence of a DC magnetic field, results in a converging beam of particles reaching a velocity above 1000 km/s. Lithium, gold, and uranium rings are considered and transient temperatures ranging from 108 to 1010 °K are expected. In the presence of deuterium and tritium fusion reactions will occur and the capture of the released neutrons may result in the synthesis of heavier elements. The considered device lends itself to a varied treatment allowing to consider velocities in the range of 2000 km/s.

Explicit relations are developed to estimate the outflux of migrating isotopomers iQF6 to the outskirts of a supersonic supercooled free jet whose core is irradiated by a co-axial laser beam and intercepted by a skimmer that separates core gas from peripheral gases. The QF6 target gas is diluted in carrier gas G (G = He, N2, Ar, Xe, SF6, etc.) which determines the jet's supersonic characteristics and forms QF6:G dimers at low temperatures. Under isotope-selective laser excitation, excited iQF6* convert their vibrational energy V into kinetic energy T after forming transient iQF6*:G dimers that dissociate in sub-microseconds. Three migrating groups with different transport parameters are created in the jet: thermal monomers, faster-moving epithermal monomers, and slower-moving dimers. Jet-core-fleeing QF6 is enriched in iQF6 due to enhanced outwards migration of iQF6! epithermals and reduced escape of jQF6:G dimers in the jet. Isotope enrichments in the rim gases are highest for heavier carrier gases such as G = Xe or G = SF6.

The requirements of matching shell ICF target parameters, parameters of compressing, and triggering drivers under direct (fast) ignition are developed. Thin shell target, which represents a shell-ablator with a DT-ice layer, frosted on the inner surface of the shell are considered. Design of a target which ensures the energy supply from the triggering driver to the central part of thermonuclear fuel, in both spherical and cylindrical geometry is developed. Spherical target is furnished with one or two conical channels for the injection of the triggering driver radiation. The ends of the cylindrical target are protected by heavy material walls that have the holes of the radius equal to the final radius of compressed fuel. It was found that the parameters of fast ignition spherical and cylindrical targets, which provide high thermonuclear gain of 500–2000 in the range of the compressing driver energy of 1–10 MJ, may be matched with the drivers parameters at low aspect ratios of the targets, 10–20. The operation of spherical targets at the moderate radius convergence ratio of 15–20, may be provided at the triggering driver energy not higher than 30 kJ. The operation of cylindrical target with spin-oriented DT-fuel at radius convergence ratio of 20–25 may be provided at 150–200 kJ of the triggering driver energy.