Laser–plasma interaction and hot electrons have been characterized in detail in laser irradiation conditions relevant for direct-drive inertial confinement fusion. The experiment was carried out at the Gekko XII laser facility in multibeam planar target geometry at an intensity of approximately $3\times {10}^{15}$ W/cm2. Experimental data suggest that high-energy electrons, with temperatures of 20–50 keV and conversion efficiencies of $\eta <1\%$, were mainly produced by the damping of electron plasma waves driven by two-plasmon decay (TPD). Stimulated Raman scattering (SRS) is observed in a near-threshold growth regime, producing a reflectivity of approximately $0.01\%$, and is well described by an analytical model accounting for the convective growth in independent speckles. The experiment reveals that both TPD and SRS are collectively driven by multiple beams, resulting in a more vigorous growth than that driven by single-beam laser intensity.

The transmitted and reflected second harmonics (SH) generation by an oblique p-polarized laser pulse irradiated on vacuum-magnetized plasma interface is investigated. The laser pulse propagates through a homogenous, underdense, and transversely magnetized plasma. The transverse magnetic field plays the role of a self-generated magnetic field produced in laser plasma interaction. It is shown that if the transmitted and reflected SH components investigated as a simultaneous process, the maximum SH power deviates from previous reports specially near the critical angle. The deviation increases with laser field intensity and plasma density. The results reveal that the conversion efficiency increases slightly by increasing incident angle and drastically enhances near the critical angle. We show that the transmitted SH power decreases by increasing the magnetic field strength, in contrast to the normal incidence, which the SH power is increased. The comparison revealed that the SH efficiency is greater for transmitted component, while the reflected component is more proper for technical and experimental applications. This paper not only conforms the previous reports for angle far from the critical but also modifies them for the SH generation near the critical angle. Moreover, this paper gives a new insight for SH generation by a magnetized plasma.

This paper presents an investigation of self-focusing of intense Gaussian rippled laser beam in collisionless plasma by including the nonlinearity associated with the relativistic mass and the ponderomotive force and its effects on the excitation of ion acoustic wave. The growth of ripple, riding on an intense Gaussian laser beam in plasma and its coupling with ion acoustic wave has also been studied. Modified coupled equations for main laser beam, growth of laser ripple in plasma, rippled laser beam, beam width, and density perturbation associated with ion acoustic wave are derived using Wentzel-Kramers-Brillouin and paraxial ray approximation. These coupled equations are solved analytically and numerically to study the laser intensity in plasma and the variation of amplitude of the ion acoustic wave for various established laser and plasma parameters. From numerical computation, it is observed that both nonlinearities significantly affected the dynamics of the growth of laser ripple in plasma, propagation of rippled laser beam as well as ion acoustic wave in plasma at high laser power flux. The growth of laser ripple increase with increase in the intensity of laser beam and due to the contribution of growth rate, intensity profile of rippled laser beam and ion acoustic wave modified accordingly.

In this paper, the opacity of plasma in local thermodynamic equilibrium condition was investigated numerically. The plasma was assumed to be produced by interaction of high power pulse laser with carbon and aluminum. Spectrally resolved opacities under different plasma temperature and density conditions were calculated and radiative absorption due to three absorption mechanisms; inverse bremsstrahlung, photo-ionization, and line absorption in plasmas was studied numerically. The purpose of this study is to calculate the values of absorption for inverse bremsstrahlung and photo-ionization processes for aluminum and carbon plasmas and to compare them for those of cold matter. In this investigation, the influences of density and temperature on plasma absorption were evaluated. The calculation results show that the opacity strength strongly depends on the plasma temperature and density.

In this paper the classical theory of Above Threshold Ionization (ATI) in the oxygen plasma was used to show how the residual electron energy depends on the laser parameters such as pulse length, wavelength and peak intensity. The value of ATI energy is found to increase with laser wavelength and its intensity. Our study conducted for three cases of τ > 2π/νp, τ = 2π/ωp, and τ < 2π/ωp, where ωp is the plasma frequency, reveals that the ATI energy is decreased for the pulse duration τ ≠ 2π/ωp. Also it is showed how the space charge effect can reduce the residual electron energy to a minimum value, in a suitable condition. By optimizing various parameters, we can generate the cold electrons suitable for the recombination x-ray laser.

Laser plasma experiments, which demonstrated the single order diffraction property of spectroscopic photon sieve (a novel single-order diffraction grating), were performed on the SILEX-I femto-second laser facility. High-intensity laser radiation was focused onto a Cu target to generate plasma. The spectra of soft X-ray from copper plasmas have been measured with spectroscopic photon sieve based spectrograph. The results show that the spectroscopic photon sieve is able to provide soft X-ray spectrum free from higher-order diffraction components. The measured spectra obtained with such a spectroscopic photon sieve need no unfolding process to extract higher-order diffraction interference.

The goal of this theory is to study the conversion of a fraction of a laser beam to its phase-mismatch second and third harmonics. This conversion takes place by focusing an intense laser beam into a transversely magnetized plasma, as a nonlinear medium. The influence of the polarization field is considered, however, the plasma density is below the critical density. It has already been revealed that for dense plasma, the second and third harmonics efficiencies decreased with density increasing in the presence of a sufficiently strong magnetic field. This result is in contrast to the under dense and weakly magnetized plasma, which the harmonics efficiencies increased with density increasing. It is shown that the harmonics radiation cut-off, when the magnetic field increases up until the saturation strength Bsat. In addition, the results indicated that the average phase-mismatch third harmonic conversion efficiency is a little smaller than the phase-match case reported for non-magnetized plasma.

This article presents the cross-focusing of two high power dark hollow Gaussian beams in plasma when relativistic nonlinearity is operative. A paraxial like approach has been used in the present analysis. In this study, the non-linear dielectric function has been expanded in terms of radial distance from the maximum of the irradiance, rather than from the axis, as is the case of Gaussian beams. The nature of propagation of a hollow Gaussian beam propagating in plasmas has been studied under the influence of relativistic non-linearity. The effect on the order (n) of hollow Gaussian beam on the cross-focusing of two beams has been explored in relativistic non-linearity in this publication.

Quasi-monoenergetic electron beams of energies 12 MeV to over 200 MeV are generated from both nitrogen and helium gas targets with 7TW laser pulses. Typically nitrogen gas interactions lead to electron bunches in the range of 12 to 50 MeV varying from shot to shot. Helium gas leads to higher energy electron bunches from 25 to 100 MeV. Occasionally exceptionally high energy bunches of electrons up to 200 MeV are observed from nitrogen and helium. Initial full two-dimensional simulations indicate the production of 20–30 MeV electron energy bunches for the typical interaction conditions as the electrons are injected from wave breaking in the plasma wake behind the laser pulse and injected into the strong electric field gradient propagating with the optical pulse. This is consistent with the experimental observations from the majority of shots. Pulse compression during propagation in the high density plasma does not allow the threshold conditions for the full bubble regime to be reached. However, the electric acceleration field in the wakefield cavity is still sufficient to lead to the formation of a bunch of electrons with an energy peak in the range of 20 to 30 MeV. In order to explain the occasional high energy shots most likely a lower density channel created by the laser prepulse may occasionally form a natural low density electron guide channel giving ideal conditions for acceleration over much longer lengths leading to the high energies observed.

An investigation is made of the role of hollow atoms in the spectra of an ultrashort-pulse-laser-driven Ar cluster target. Experimental measurements are presented from an Ar cluster-gas target using short-pulse lasers with various intensities, durations, and contrasts. Calculations in support of these measurements have been performed using a detailed atomic kinetics model with the ion distributions found from solution of the time-dependent rate equations. The calculations are in good agreement with the measurements and the role of hollow atoms in the resulting complicated spectra is analyzed. It is demonstrated that, although the presence of hollow atoms is estimated to add only around 2% to the total line emission, signatures of hollow atom spectra can be identified in the calculations, which are qualitatively supported by the experimental measurements.

In the present investigation, the excitation of an upper hybrid wave (UHW) in a hot collisionless magneto-plasma by a relativistic laser beam propagating perpendicular to the static magnetic field and having its electric vector polarized along the direction of the static magnetic field (ordinary mode) is presented. Due to nonuniform intensity distribution of pump laser, the background electron concentration is modified. The amplitude of the UHW, which depends on the background electron concentration, is thus nonlinearly coupled with the laser beam. The effect of nonlinear coupling between the pump laser and UHW is studied. The effect of the relativistic electron mass nonlinearity and the relativistic self-focusing of the pump laser on the excitation of the UHW have been incorporated. The dynamics of the excitation of the UHW in different power domains of the laser beam is accordingly modified. It has been seen that the effect of changing the strength of the static magnetic field on the nonlinear coupling and the dynamics of the excitation of the UHW is significant. The focusing behavior of the UHW may find its relevance in the heating of plasmas near the upper hybrid resonance.

Laser plasma interaction experiments have been performed using an fs Titanium Sapphire laser. Plasmas have been generated from planar PMMA targets using single laser pulses with 3.3 mJ pulse energy, 50 fs pulse duration at 800 nm wavelength. The electron density distributions of the plasmas in different delay times have been characterized by means of Nomarski Interferometry. Experimental data were compared with hydrodynamic simulation. First results to characterize the plasma density and temperature as a function of space and time are obtained. This work aims to generate plasmas in the warm dense matter (WDM) regime at near solid-density in an ultra-fast laser target interaction process. Plasmas under these conditions can serve as targets to develop X-ray Thomson scattering as a plasma diagnostic tool, e.g., using the Vacuum ultraviolet (VUV) free-electron laser (FLASH) at Dentsches Elektronen-Synchrotron (DESY) Hamburg.

Some preliminary views are presented to the topic “Fast High Density Plasma Blocks Driven by Picosecond Terawatt Lasers” of the UWS-International Workshop 1–4 December 2004 in Sydney, Australia, underlining the motivation to explain the difference between the relativistic and the subrelativistic effects of ps-laser pulse interaction with plasma at powers above TW. This refers to specifically selected experimental and theoretical presentations at the workshop containing results for explaining the differences but also the important applications for studies on the fast ignitor scheme for application on nuclear fusion energy. One of the aims with relativistic proton beams is to realize conditions of spark ignition, while the subrelativistic case implies the generation of fast plasma blocks eventually with the possibility to ignite a fusion flame in uncompressed solid DT fuel for a power station with high efficiency.

Basic properties of generation of high-current ion beams using the skin-layer ponderomotive acceleration (S-LPA) mechanism, induced by a short laser pulse interacting with a solid target are studied. Simplified scaling laws for the ion energies, the ion current densities, the ion beam intensities, and the efficiency of ions' production are derived for the cases of subrelativistic and relativistic laser-plasma interactions. The results of the time-of-flight measurements performed for both backward-accelerated ion beams from a massive target and forward-accelerated beams from a thin foil target irradiated by 1-ps laser pulse of intensity up to ∼ 1017 W/cm2 are presented. The ion current densities and the ion beam intensities at the source obtained from these measurements are compared to the ones achieved in recent short-pulse experiments using the target normal sheath acceleration (TNSA) mechanism at relativistic (>1019 W/cm2) laser intensities. The possibility of application of high-current ion beams produced by S-LPA at relativistic intensities for fast ignition of fusion target is considered. Using the derived scaling laws for the ion beam parameters, the achievement conditions for ignition of compressed DT fuel with ion beams driven by ps laser pulses of total energy ≤ 100 kJ is shown.

It is known that relativistic laser plasma interactions can already today induce accelerating fields beyond some TV/m, which are indeed capable to efficiently accelerate plasma background electrons as well as protons. An introduction to the current state of the art will be given and possible applications of these optically induced charged particle sources will be discussed.