This issue of Laser and Particle Beams includes papers presented at the Workshop on “Fast High Density Plasma Blocks Driven by Picosecond Terawatt Lasers” held at the University of Western Sydney, Campbelltown Campus, Australia from 1–4 December 2004.

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 shown that the effective hot electron temperature, Thot, associated with the energetic electrons produced during the interaction of an ultra-intense laser with thin solid targets is dependent on the thickness of the target. We report the first direct experimental observations of electron energy spectra obtained from laser-solid interactions that indicates the reflexing of electrons in thin targets results in higher electron temperatures than those obtained in thick target interactions. This can occur for targets whose thickness, xt, is less than about half the range of an electron at the energy associated with the initial effective electron temperature, provided the laser pulse length is at least cτp > 2xt. A simple theoretical model that demonstrates the physical mechanism behind this enhanced heating is presented and the results of computer simulations are used to verify the model.

Propagation of ultrashort intense laser pulses in a plasma Bragg grating induced by two counterpropagating laser pulses has been investigated. Such a plasma grating exhibits an ultrawide photonic band gap, near which strong dispersion appears. It is found that the grating dispersion dominates the dispersion of background plasma by several orders of magnitude. Particle-in-cell (PIC) simulations show light speed reduction, pulse stretching, and chirped pulse compression in the plasma grating. The nonlinear coupled-mode theory agrees well with the PIC results. Because the plasma grating has a much higher damage threshold than the ordinary optical elements made of metal or dielectric, it can be a novel tool for controlling femtosecond intense laser pulses.

Generation of high speed dense plasma blocks is well known from hydrodynamic theory and computations (PIC) with experimental confirmation by Badziak et al. (2005) since ps laser pulses with power above TW are available. These blocks may be used for fusion flame generation (thermonuclear propagation) in uncompressed solid state deuterium and tritium for very high gain uncomplicated operation in power stations. Hydrodynamic theory from computations from the end of 1970s to recent, genuine two fluid computations support the skin layer accelerations (SLA), by nonlinear (ponderomotive) forces as measured now in details under the uniquely selected conditions to suppress relativistic self-focusing by high contrast ratio and to keep plane geometry interaction. It is shown how the now available PW-ps laser pulses may provide the very extreme conditions for generating the fusion flames in solid state density DT.

In this paper the results of numerical computations of rippling smoothing basing on the broad-band laser irradiation method for the laser intensity range 1016−1017 W/cm2 and short-pulse (<10 ps) interaction with plasma are described.

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.

Studies of single-event laser-target interaction for fusion reaction schemes leading to volume ignition are discussed. Conditions were explored where single-event ns-laser pulses give rise to temperatures sufficient for volume ignition. Thus, ignition is possible, particularly if X-ray reabsorption is sufficiently high. Unfortunately, this scheme requires laser pulses with energies above 5 MJ and target densities of compressed DT above 1000 g/cm−3. Both requirements are quite demanding for near term systems. Nevertheless the present state technology and the detailed knowledge about volume ignition at direct drive are a basis. Systems as NIF or LMJ can well confirm these physics-clarified conditions and the technology for large laser systems with sufficient repetition rate and for a drastic reduction of the size and costs is necessary and possible and by physics similar to the known reductions in transistor development.

The studies of laser ablation have lead to a new theory of nuclei, endothermic nuclei generation, and quark-gluon plasmas. The surface of ablated plasma expanding into vacuum after high power laser irradiation of targets contains an electric double layer having the thickness of the Debye length. This led to the discovery of surface tension in plasmas, and led to the internal dynamic electric fields in all inhomogeneous plasmas. The surface tension causes stabilization by short length surface wave smoothing the expanding plasma plume and to stabilization against the Rayleigh–Taylor instability. Generalizing this to the degenerate electrons in a metal with the Fermi energy instead of the temperature resulted in the first quantum theory of surface tension of metals in agreement with measurements. Taking the Fermi energy in the Debye length for nucleons results in a theory of nuclei with stable confinement of protons and neutrons just at the well-known nuclear density, and the Debye lengths equal to the Hofstadter decay of the nuclear surface. Increasing the nuclear density by a factor of 10 leads to a change of the Fermi energy into its relativistic branch where no surface energy is possible and the particle mass is not defined, permitting the quark gluon plasma. Expansion of this higher density at the big bang or in super-nova results in nucleation and element generation. The Boltzmann equilibrium permits the synthesis of nuclei even in the endothermic range, however with the limit to about uranium. A relation for the magic numbers leads to a quark structure of nuclear shells that can be understood as a duality property of nuclei with respect to nucleons and quarks

The measurement of very narrow high density plasma blocks of high ion energy from targets irradiated with ps-TW laser pulses based on a new skin depth interaction process is an ideal tool for application of ion implantation in materials, especially of silicon, GaAs, or conducting polymers, for micro-electronics as well as for low cost solar cells. A further application is for ion sources in accelerators with most specifications of many orders of magnitudes advances against classical ion sources. We report on near band gap generation of defects by implantation of ions as measured by optical absorption spectra. A further connection is given for studying the particle beam transforming of n-type semiconductors into p-type and vice versa as known from sub-threshold particle beams. The advantage consists in the use of avoiding aggressive or rare chemical materials when using the beam techniques for industrial applications.

Success in inertial confinement fusion (ICF) requires sophisticated, characterized targets. The increasing fidelity of three-dimensional (3D), radiation hydrodynamic computer codes has made it possible to design targets for ICF which can compensate for limitations in the existing single shot laser and Z pinch ICF drivers. Developments in ICF target fabrication technology allow more esoteric target designs to be fabricated. At present, requirements require new deterministic nano-material fabrication on micro scale.

This paper will present the nonlinearity and dispersion effects involved in propagation of optical solitons, which can be understood by using a numerical routine to solve the nonlinear Schrödinger equation (NLSE). Here, Mathematica v5© (Wolfram, 2003) is used to explore in depth several features of optical solitons formation and propagation. These numerical routines were implemented through the use of Mathematica v5© and the results give a very clear idea of this interesting and important practical phenomenon. It is hoped that this work will open up an important new approach to the cause, effect, and correction of interference from secondary radiation found in the uses of soliton waves in lasers and in optical fiber telecommunication. It is believed that these results will be of considerable use in any work or research in this field and in self-focusing properties of the soliton (Osman et al., 2004a, 2004b; Hora, 1991). In a previous paper on this topic (Beech & Osman, 2004), it was shown that solitons of NLSE radiate. This paper goes on from there to show that these radiations only occur in solitons derived from cubic, or odd-numbered higher orders of NLSE, and that there are no such radiations from solitons of quadratic, or even-numbered higher order of NLSE. It is anticipated that this will stimulate research into practical means to control or eliminate such radiations.

High energy heavy ions were generated in laser produced plasma at moderate laser energy, with a large focal spot size of 0.5 mm diameter. The laser beam was provided by the 10 GW GSI-NHELIX laser systems, and the ions were observed spectroscopically in status nascendi with high spatial and spectral resolution. Due to the focal geometry, plasma jet was formed, containing high energy heavy ions. The velocity distribution was measured via an observation of Doppler shifted characteristic transition lines. The observed energy of up to 3 MeV of F-ions deviates by an order of magnitude from the well-known Gitomer (Gitomer et al., 1986) scaling, and agrees with the higher energies of relativistic self focusing.

Two-dimensional (2D) FLASH simulations were run with Spitzer-Härm conductivity on and off in an attempt to simulate a laser-produced blast wave. Dissociation, ionization, recombination, and radiative cooling were not included. An initial Gaussian temperature profile with T0 = 120 eV and spot radius r0 = 25 μm was used assuming 1 μm thickness of the CH disk is ablated into the background nitrogen gas. Evolution of the blast wave differs slightly between the cases of Spitzer-Härm on and off, and neither case matches well with experiment. Due to the high temperatures involved, a thermal wave should be expected such that the Spitzer-Härm conductivity on case is more likely. A simulation run with an initial temperature of ∼ 4 keV might match better with experiment.

Characteristics of two-element (PbMg) laser generated plasma ions were studied using a mass-spectrometer. It was found that increasing the fraction of Mg leads to widening of the energy spectra of Pb ions by more than a factor of two, while the intensity of Pb ions of all charge states does not depend on the Mg fraction. This effect is explained by the friction existing between light and heavy ions during their expansion away from the target.

Recently, warm dense matter has emerged as an interdisciplinary field that draws increasing interest in plasma physics, condensed matter physics, high pressure science, astrophysics, inertial confinement fusion, as well as material science under extreme conditions. To allow the study of well-defined warm dense matter states, we introduced the concept of idealized slab plasma (ISP) that can be realized in the laboratory via (1) the isochoric heating of a solid and (2) the propagation of a shock wave in a solid. The application of this concept provides new means for probing AC conductivity, equation of state, ionization, and opacity. These approaches are presented here using results derived from numerical simulations.

The paper presents the first experimental results obtained by using new gamma-quantum diagnostics for ion beam induced high energy density matter. Registration of γ-quantum output from the region of beam-target interaction with time resolution enables to pick-up information on density evolution of the target even if the ionization state of matter involved is unknown.

The properties of an electron beam (e-beam) formed in air under atmospheric pressure are reported. The nanosecond generators RADAN-303 (two devices) and RADAN-220, producing nanosecond voltage pulses with amplitude of up to 400 kV and subnanosecond rise time were used in the experiments. It was shown for the first time that the duration of e-beam current of gas diode behind the foil does not exceed 0.1 ns. The maximum amplitude of current of a supershort avalanche electron beam (SAEB) behind the foil was ∼400 A. The data on the influence of various parameters on e-beam current amplitude measured behind the foil were obtained. An electron beam with energy less than 60 keV and powerful X-ray radiation were formed in discharge gap simultaneously with SAEB.

The gas discharge in a gas peaking switch was experimentally studied and numerically simulated. For simulation, the discharge was divided into two phases, gas breakdown and voltage collapse. The criterion for an electron avalanche to transit to streamer was considered as the criterion of gas breakdown. The spark channel theory developed by Rompe-Weizel was used to calculate the spark resistance. It was found that the prepulse considerably lowers the voltage pulse applied to the gap. Even for a given input pulse, the voltage pulse applied to a peaking gap is different for different gap distance due to existence of a different prepulse. In this case, the breakdown voltage of a gas peaking gap depends on gas pressure and gap distance, individually. For nitrogen pressure varying from 3 MPa to 10 MPa and gap distance from 0.6 mm to 1.2 mm, the peak electric field higher than 2 MV/cm was achieved when breakdown. The output 10% to 90% rise time, tr, varies from 145 ps to 192 ps. As gas pressure increases, tr decreases, which can be explained by the fact that the breakdown field increases with the increase of gas pressure. It was found in experiment that the jitter in tr could be attributed to the jitter in breakdown field. Instead of getting longer, the averaged experimental tr gets shorter as gap distance increases from 0.6 mm to 1.2 mm, which differs from the results of calculation and indicates there may exist something, other than electric field, that is also related to tr. The reason for this difference may lies in the inverse coefficient of spark resistance varying with gap distance. On the whole, the results from the calculations agree with the experimental ones.

A joule level of XeF(C-A) laser optically pumped by a sectioned surface discharge was developed. The irradiative intensity of pumping source was diagnosed by calculating XeF2 photo-dissociation wave evolvement which was photographed by a framing camera. The photon flux in the wavelength region of 140 to 170nm is about 5 × 1023 photon s−1cm−2, that corresponds to the irradiative brightness temperature of more than 25000 K. The laser experiments were carried out in different conditions. The maximum laser output energy of 2.5 J was obtained with the total conversion efficiency of 0.1%.