Here we study the problem of a focused laser beam propagation in plasma with the initial density, which is much higher than the critical one. The Helmholtz equations, together with the equations of single fluid hydrodynamics, with the relativistic ponderomotive force were solved. It was shown that the stable waveguide with the cross-section of wavelength size was formed when plasma was affected by the laser radiation with the intensity exceeding the critical one while the laser radiation pulse was as long as (10–100) ps.

Results of turbulent mixing research of thin Al and Au layers under laser acceleration of the three-laser targets Si/Al/Au are presented. Analyses of experimental data under the program SND-TUR, where the Nikiforov model is used for turbulent mixing description, testify to the essential impact of hot spots on the examined processes in distribution of laser radiation intensity on the surface of the target. Experimental setup on the laser beams' smoothing by the “foam” coated on the target, has been considered. The results of the first experiments are presented.

In this paper, we report on a new laser facility called PALS (Prague Asterix Laser System), which is currently under construction, and which will house the high-power iodine laser Asterix IV. Upon its completion in late 1999, the PALS facility will be capable of providing single- or multiple-pulse irradiation with a variable pulse duration ranging from 100 to 500 ps. Wavelengths available will be 1.315 μm, 658 nm, and 438 nm. The system will provide one main beam with energy up to 1200 J and two smaller auxiliary beams with a combined energy of up to 100 J. A wide variety of geometries and variable pulse timings is available. We assess PALS' potential for investigating the physics of laser plasmas in inertial confinement fusion, the development and applications of X-ray lasers, X-ray spectroscopy, and radiation transport, using multiple-pulse and extended beam capability.

Multistage, e-beam-pumped, 100 J-class KrF laser installation “GARPUN” is described with the emphases to high-power laser beam control and target irradiation experiments. The ablation pressures in the megabar range were measured and hydrodynamic flow was investigated both experimentally and by numerical simulations for laser intensities up to 5×1012 W/cm2, pulse duration of 100 ns, and focal spot diameter 150 μm. Graphite-diamond phase transformation under laser loading was observed by dynamic and Raman scattering methods. Some approaches to the fast ignition inertial confinement fusion, using the simultaneous amplification of long and short laser pulses in KrF drivers, are considered.

A novel approach for injection of a freestanding target into an ICF chamber is described which could significantly reduce both the dead volume of the target system and the fill time of cryotarget. The extremely short flight time of a target inside the ICF target chamber (less than 100 ms) allows one to keep the quality of the cryolayer up to the very moment of target irradiation. The possibility of improving the quality of the inner surface of the cryogenic layer by using the target illumination by the electron beams during the free fall of the target in the fusion chamber is also discussed.

LULI will play an important role as a major laser ICF and IFE support facility in Europe after recent or future changes (ASTERIX-Garching, CEA-Limeil) in large laser system programs. We will review the research activities which have been carried out at LULI during the last 2 years both in the nanosecond regime and in the subpicosecond ultraintense regime. As part of the LULI upgrade project, a new 30-J, 300-fs, 100-TW ultraintense laser chain has been commissioned in 1997. This laser has allowed the first complete demonstration of wakefield electron acceleration and is presently used to study new concepts in laser fusion and laser–plasma interaction experiments in the relativistic regime.

Phase conjugation process at intracavity degenerate four wave mixing of a long pulse CO2 laser radiation in its active medium has been studied experimentally. Dependencies of energetic and temporal characteristics of the phase conjugation signal upon specific energy stored into electric discharge, Q-factor of laser resonator, laser mixture composition and pressure, interaction angle, optical delay between probe and co-propagating waves, intensity ratio for these waves J3/J1, a degree of linear polarization, and laser spectrum are analyzed. Reflectivity of the phase conjugation signal is shown to increase with specific input energy rise and a decrease of the ratio J3/J1, being up to 7.5%. An increase of nitrogen content and a decrease of helium content in the laser mixture results in reflectivity rise and peculiar laser pulse profile with two maximums being due to amplitude and phase nonlinearities of the active medium. Specific input energy rise and an increase of Q-factor leads to a decrease of response time for the phase conjugation signal. Nonlinear properties of degenerate four wave mixing on amplitude gain and phase thermal diffraction gratings in the active medium of a long pulse CO2 laser are analyzed theoretically. An interconnection of nonlinear parameters of the amplifying media with the temporal behavior of phase conjugation reflectivity is determined. A comparison of the theoretical calculations and the experimental data has been done.

In the present study we performed an experimental investigation of the Rayleigh–Taylor instability (RTI) in a mixing zone between two gases entrapped into accelerated motion by a nonstationary compression wave. Acceleration g was ∼1.5·107 cm/s2, Atwood numbers ranged from 0.04 to 0.77. A mixing zone was formed by an oxygen-hydrogen mixture and an inert gas (Ne, Ar, Kr, Xe) or SF6. The initial gas pressure was 0.5 atm. A specific feature of our experiment is compressibility of media tested and initially continuous interface between gases of different densities. The present work is a continuation of investigations on nonlinear, transition, and early turbulent stages of the RTI.

In this paper, we present and discuss an extension and an improvement of the Figure of Merit (FoM) that we introduced in a previous paper. The FoM describes the effectiveness of the frequency doubling materials for ultrashort light pulse modulators via second-order cascaded effects. In the present work, as an input pulse we use a temporal Gaussian pulse so that our perturbative method allows an analytical expression even for the output pulse field after the second pass inside the crystal. For the first time together with the completely analytical expression for the second pass, we report also the exact numerical coefficients for the peak phase modulation. With the FoM it is possible to choose the more appropriate nonlinear material and the use of the cascaded interaction process. Finally, we present for the first time the FoM dependence from the wavelength in the interval 0.5–1 μm, and to a table already shown we added more nonlinear materials.

The big lasers for inertial fusion (NIF or LMJ) may be used with 2 to 3 times larger pulse energy if instead of the third harmonics, the fundamental wavelength is applied. A necessary condition especially for direct drive is then to suppress the stochastic (15 ps) pulsation of the interaction as the basic obstacle of anomalous interaction. The experiments by Maddever and the numerical analysis using the genuine two-fluid model resulted in the knowledge that appropriate application of smoothing is necessary to suppress primarily the pulsation and, to a lesser extent, the self-focusing and filamentation. With these larger laser pulses, fusion gains of 35 and above can be reached suing the very uncomplicated and robust volume ignition.

In the previous design, the maximum drive radiation temperature was 4 MK or 350 eV (Holstein 1996). Different beam configurations gave roughly the same uniformity with the NIF-size cavity. Our best configuration used four cones of beams illuminating three rings. An integrated 2D simulation pointed out that the symmetry was good enough to reach a gain of ten. Two evolutions took place in the design of our MJ laser. We moved from a capsule adapted to 4 MK (L1000) to another one adapted to 3.5 MK (L1215) in order to minimize the parametric instabilities (the cavity size is almost the same). This new capsule also has a better hydrostability according to the “classical modelling” (Lindl 1995). The second evolution is a simplification of the target chamber. We restricted ourselves to two major configurations for indirect drive (two-ring and three-ring configurations). Therefore, only three cones of beams are necessary instead of five cones in the first design. Finally, the number of holes in the chamber is 80 instead of 100.

In this work, the Saha equation is solved using atomic data provided by means of analytical potentials to calculate the ionization state and ion abundances for local thermodynamic equilibrium (LTE) plasmas of Al, Fe, and Au. The plasma effects are taking into account using an analytical potential which includes plasma effects. The problem of the cut off partition functions in the Saha equation is also analyzed using three different criteria. Finally, some opacity calculations are performed.

This work proposes an analytical perturbative method describing the effects on the propagation of finite aperture beams due to the self-phase and self-amplitude modulation which result from cascaded second order interaction of ultrashort light pulses. The method merges the semi-analytical solution with a perturbative beam propagation technique, namely the Gaussian Beam Decomposition, which describes the effects of the non linear modulation on the free beam propagation. In particular we have studied the problem of the time- and intensity-dependent transmission of the pulse through slits or apertures placed along the path of the beam simulating a geometry suitable for passive laser mode-locking. Although an efficient pulse shortening action can be obtained in stationary conditions, in non stationary conditions the occurrence of an unavoidable amplitude modulation perturbs the beam propagation and reduces the temporal selectivity of the modulator.

Presently, a great part of the attention paid to the studies on the Richtmyer–Meshkov instability (RMI) is focused on the case of shock passage through a system of gas layers of different densities. The interest to this problem has been induced, in particular, by multiple attempts to minimize the process of mixing between the layers of different densities in targets for inertial confinement fusion (ICF), caused by excitation of the RMI on the layer boundaries. The RMI suppression is one of the most important, but difficult problems in worldwide efforts on ICF. A direct investigation of this phenomenon in laser experiments (in NOVA, for example) is a rather difficult task. Shock tubes are a more promising tool for modeling the impulsively-driven instabilities in gas layers, for they allow us a detailed investigation of the mechanism of initiation and the pathways of evolution of the instability (Jacobs et al. 1995; Aleshin et al. 1995a). A series of shock-tube experiments for the shock passage through a system of gas layers of different densities has been carried out. The effect of a suppression of the RMI has been found. A 2.5-fold reduction of the mixing region thickness in the presence of the layer as compared to the thickness without it has been obtained.

Several choices exist in the design and production of capsules intended to ignite and propagate fusion burn of the deuterium–tritium (D–T) fuel when imploded by indirect drive at the National Ignition Facility (NIF). These choices include ablator material, ablator dopant concentration and distribution, capsule dimensions, and X-ray drive profile (shock timings and strengths). The choice of ablator material must also include fabrication and material characteristics, such as attainable surface finishes, permeability, strength, transparency to radio frequency and infrared radiation, thermal conductivity, and material homogeneity. Understanding the advantages and/or limitations of these choices is an ongoing effort for LLNL and LANL designers. At this time, simulations in one-, two-, and three-dimensions show that capsules with either a copper-doped beryllium or a polyimide (C22H10N2O4) ablator material have both the least sensitivity to initial surface roughnesses and favorable fabrication qualities. Simulations also indicate the existence of capsule designs based on these ablator materials which ignite and burn when imploded by less than nominal laser performance (900-kJ energy, 250-TW power, producing 250-eV peak radiation temperature). We will describe and compare these reduced-scale capsules, in addition to several designs which use the expected 300-eV peak X-ray drive obtained from operating the NIF laser at 1.3 MJ and 500 TW.

The interaction of powerful laser and X-ray pulses with planar low average density (0.5–10 mg/cm3) porous agar-agar targets was experimentally studied. At a laser power density of ∼5 × 1013 W/cm2 (λ = 1.054 μm) the laser light absorption and following energy transfer processes, as well as dynamics of produced plasma were investigated in detail with a variety of optical and X-ray diagnostic methods. Volume absorption is shown to occur in experiments with laser-irradiated agar targets. An extended laser energy deposition region filled with hot (0.8–1 keV) plasma is formed inside a porous target. The laser light absorption efficiency is as high as ∼80%. The emission of 2ω0 and 3ω0/2 harmonics from laser-produced plasma is observed over the time of the laser pulse even with agar targets of 0.5 mg/cm3 average density. Characteristics of energy transfer in low-density porous media are measured in experiments on illumination of agar targets by laser pulses or X rays emitted by a thin Cu converter. The hydrodynamic mechanism is responsible for the energy transfer in laser-illuminated porous targets and the radiative energy transfer seems to be dominant in the case of X-ray irradiation. The experimental data are in reasonable agreement with predictions of a developed theoretical model describing the hot plasma layer formation and the two-stage homogenization process within the illuminated porous targets.

We demonstrate that short laser pulse self-guiding over distances of many Rayleigh lengths can be achieved in the absence of any focusing nonlinearity as a result of trapping of a leaking wave in a plasma channel produced by field-induced ionization in the saturation regime. A detailed computational study of the new self-guiding effect in both cases of comparatively long laser pulses, when the traditional approximation of the slowly varying complex amplitude is valid, and of high intense ultrashort laser pulses comprising only few field cycles have been performed.

We describe two approaches to the design of a direct-drive high-gain pellet for inertial confinement fusion reactors that has enhanced stability due to the reduction in the Rayleigh-Taylor growth rate and enhanced thermal smoothing of laser imprint. The first design incorporates an overcoat containing a high-Z element that radiatively heats the ablator during the foot of the laser pulse. The second incorporates a very low density foam ablator that is compressed by a series of transmitted and reflected shocks. Both designs enhance thermal smoothing by developing a very long density scale length and high electron densities in the ablator blowoff.

2D arrays of laser diodes were developed and investigated under QCW operating conditions. Output power and energy density up to 1 kW/cm2 and 0.45 J/cm2 (at pulse duration 0.5 ms) were measured at the wavelength 810 nm. The spectral composition of radiation, shape of the output pulses, and far-field and near-field radiation zones were examined under various pumping parameters. The kinetics of the temperature profiles in monolithic QCW AlGaAs/GaAs linear bars and 2D arrays, emitting at the wavelength 810 nm was modeled numerically. Quasi-CW and CW operation under various pump parameters were considered as a function of a heat sink design. A calculation model was used to interpret the experimental dependences of the output parameters of the arrays on the pump conditions for application in the solid-state laser driver project. The limit of total power conversion efficiency of diode lasers was analyzed in respect of the threshold current density, series resistance and external differential quantum efficiency. The estimated maximum value of 75% was obtained for the present technological level of the diode lasers production. The corresponding limit of the output optical power density of 2D laser array was defined around 10 kW/cm2.

Holographic methods developed to study the behavior of surfaces shocked by high power lasers are reported. Shock waves of the order of hundreds of kilobars are generated in Sn targets 50-μm thick, by a Nd:YAG laser system with a wavelength of 1.06 μm, a pulse duration of 7.5 ns FWHM, and irradiance in the range (1.0–2.6)·1013 W/cm2. Two configurations of off-axis holography were applied: holograms based on forward scattering, and holograms of both backward and forward scattering. The hologram is produced by scattering of a pulse, 6.7 ns (FWHM), of green laser light synchronized with the laser that generates the shock wave. Holograms of the topology of the rear surface of shocked Sn targets moving in vacuum and in air (at atmospheric pressure) are reported.