This issue of Laser and Particle Beams contains a selection of papers presented at the International Workshop on Laser and Plasma Accelerators held at Portovenere, Italy, from September 29 to October 3, 2003. The papers were subjected to the regular refereeing procedure, in conformity with the publication standards concerning originality and quality of presentation for articles in this journal. The papers published here do not cover the full workshop program and therefore do not constitute proceedings in the normal sense. The Workshop was the last in a series sponsored by the International Committee for Future Accelerators to promote international collaboration in the study, development, and exploitation of advanced and novel accelerators.

The International Conference on “Ultrashort High-Energy Radiation and Matter” has been held in Villa Monastero, Varenna, Italy, during October 7–10, 2003. The conference has been jointly organized by the “Piero Caldirola” International Centre for the Promotion of Science and International School of Plasma Physics, Milan, Italy, and by the FEMTO Programme of the European Science Foundation (chaired by Prof. Charles Joachain of the University of Bruxelles).

Recent advances of the photon kinetic theory are illustrated here, with examples taken from plasma physics (forward Raman scattering), and from nonlinear optics (self-phase modulation). This theory can provide a unified view of nonlinear optical phenomena involving photon beams with an arbitrary spectrum.

This issue of Laser and Particle Beams includes papers presented at the “Workshop on Simulations of Ultra Intense Laser Beams Interaction with Matter” held in Bordeaux, France, from 14 to 16 April, 2003. This workshop was organized jointly by the Polytechnic University (Madrid, Spain), University of Bordeaux 1 (Talence, France), University of Milano-Bicocca (Milan, Italy), and Commissariat à l'Energie Atomique (CEA, France), sponsored by the European Science Foundation (ESF), University of Bordeaux 1, and CEA.

We present a Ramsey technique using high-order harmonics for high-resolution atomic spectroscopy in the extreme ultraviolet. Pairs of time-delayed and phase-coherent harmonic pulses generated by the interaction of ultrashort and intense laser pulses with a noble gas are used to study excited states of krypton.

The results from theoretical and experimental studies, as well as from 2.5-dimensional (2.5-D) numerical simulation of plasma wake field excitation, by either relativistic electron bunch, laser pulse, and the charged particle wake field acceleration are discussed. The results of these investigations make it possible to evaluate the potentialities of the wake field acceleration method and to analyze whether it can serve as a basis for creating a new generation of devices capable of charged particle accelerating at substantially higher (on the order of two to three magnitudes) rates in comparison with those achievable in classical linear high-frequency (resonant) accelerators.

The concept of fast ignition of precompressed pellets for inertial confinement fusion is presented and the main approaches are discussed. Numerical simulations of fast coronal ignition and the peculiarities of this scheme are considered in detail. Particular attention is devoted to the energy transport in the pellet corona. It is shown that fast coronal ignition will be successful only if the energy deposition by the fast electrons is anomalous over a sufficiently extended overdense region. Alternative schemes are briefly discussed.

The transport of hot electrons in solid density plasma created by a high-intensity subpicosecond laser pulse and the resulting heating and ionization of the bulk of plasma are simulated with the electron kinetic code “FPI.” Both the hot and the thermal electrons are treated kinetically. An analysis of the results in terms of a two Maxwellians fit to the numerically obtained distribution function is made.

Nonlocal electron heat transport in plasmas heated by a high-intensity laser field is investigated. We show how the heat transport is strongly modified by the super-Gaussian character of the energy distribution caused by the strong collisional heating. The change in the collisional electron–ion energy exchange due to this modification of the shape of the electron distribution function is also studied.

At high laser intensities, three step recollision processes such as high order harmonic generation and high-order ATI, are normally severely suppressed due to the magnetic field component of the laser pulse. However, if the laser pulse and relativistic ion beam are directed against each other, a significant increase in the frequency and the intensity of the pulse in the rest frame of the ions can occur. By performing calculations based on a Coulomb-corrected nondipole strong field approximation, we have shown that there is a range of intensities, Lorentz factors, and ion charges for which the suppression of the three step recollision processes is not severe, even for ponderomotive energies exceeding 10 keV. As an example, we consider parameters relevant to the accelerator that will be built at GSI-Darmstadt, capable of accelerating multicharged ions to Lorentz factors reaching 30.

In this paper, we report the first results of dosimetric analysis of broad-spectrum, multi-MeV laser accelerated proton beams obtained during experiments at the Rutherford Appleton Laboratory using the Chirped Pulse beam of the Vulcan laser. The spectra are retrieved by a numerical analysis that allows the reconstruction of the energetic profile of the proton beam from data obtained using radiochromic film.

The structure of large clusters such as neutral clusters, metallic clusters, and clusters ion is investigated. Furthermore, the electron distribution of large clusters when they are irradiated by an intense ultrashort laser pulse is treated. The cluster excitation results from the interaction of the electron subsystem with the laser field. Analyzing the quantum metallic cluster proves that its properties differ essentially from the properties of a classical small metallic sphere. The eigen frequency of the surface oscillation of a cluster is obtained and it is shown that it is lower than Mie frequency because of Thomas–Fermi screening.

In the context of the French Laser Mégajoule (LMJ) fusion research program, direct drive is an alternate to indirect drive to reach ignition and thermonuclear burn. We present recent progress in the direct-drive fusion studies for LMJ. Calculations have shown that the LMJ irradiation uniformity is characterized by long wavelength asymmetries compatible with direct drive requirements. Calculations of the irradiation uniformity in the context of indirect drive beam positioning have been done. We show that non-uniformity can be minimized by repointing the beams. Unfortunately, a time analysis shows that this nonuniformity increases strongly in time above levels usually considered inconsistent for direct drive. Finally, a recent baseline target design is presented and consists of a DT ice shell surrounded by a low-density CH foam wicked with cryogenic DT. This design can potentially reach a gain of 90 with a 1-MJ on-target laser driver. Hydrodynamic stability is increased at the ablation front and the laser–target coupling efficiency achieves 85%.

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.

Energetic ion beams are produced during the interaction of ultrahigh-intensity, short laser pulses with plasmas. These laser-produced ion beams have important applications ranging from the fast ignition of thermonuclear targets to proton imaging, deep proton lithography, medical physics, and injectors for conventional accelerators. Although the basic physical mechanisms of ion beam generation in the plasma produced by the laser pulse interaction with the target are common to all these applications, each application requires a specific optimization of the ion beam properties, that is, an appropriate choice of the target design and of the laser pulse intensity, shape, and duration.

We report results from a study of the integrated column density and expansion dynamics of ground-state-selected Ba+ ions in a laser–plasma plume using a new experimental system—VPIF (vacuum-ultraviolet photoabsorption imaging facility). The ions are tracked by recording the attenuation of a pulsed and collimated vacuum ultraviolet beam, tuned to the 5p–6d inner-shell resonance of singly ionized barium, as the expanding plasma plume moves across it. The attenuated beam is allowed to fall on a CCD array where the spatial distribution of the absorption is recorded. Time-resolved ion velocity and integrated column density maps are readily extracted from the photoionization images.

Modern experimental methods and instruments for X-ray spectral investigation of hot dense plasma provide complex information on environmental conditions in extreme states of matter. The basic spectroscopic conceptions for K-shell plasma diagnosis are outlined, the main characteristics of toroidally bent crystal spectrometers and vertical-dispersion instruments are briefly reviewed. Selected applications (monitoring and optimization of the emission from the femtosecond-laser-produced plasmas, characterization of colliding laser-exploded foils, spectral line merging, and continuum lowering in constrained-flow plasmas) demonstrate the usefulness of advanced spectroscopic methods for plasma diagnostics and fundamental research.

This paper emphasizes the energy dissipation through collective electromagnetic modes (mostly transverse to the incoming beam) of ultraintense relativistic electrons and nonrelativistic protons interacting with a supercompressed core of deuterium + tritium (DT) thermonuclear fuel. This pattern of beam–plasma interaction documents the fast ignition scenario for inertial confinement fusion.

The electronmagnetic Weibel instability is considered analytically in a linear approximation. Relevant growth rates parameters then highlight density ratios between target and particle beams, as well as transverse temperatures. Significant refinements include mode–mode couplings and collisions with target electrons. The former qualify the so-called quasi-linear (weakly turbulent) approach. Usually, it produces significantly lower growth rates than the linear ones. Collisions enhance them slightly for kc /ωp < 1, and dampen them strongly for kc /ωp ≥ 1. Those results simplify rather drastically for the laser-produced and nonrelativistic proton beams. In this case, those growth rates remain always negative through a wide range of beam–target parameters.

High-resolution K-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters have been measured with an intensity above 1019 W/cm2 and a pulse duration of 30 fs. The total photon flux of 2 × 108 photons/pulse was achieved for Heα1 resonant line of Ar (λ = 3.9491 Å, 3.14 keV). In parallel with X-ray measurements, energy distributions of emitted ions have been measured. The multiply charged ions with kinetic energies up to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoric heating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield of the He-like argon ion and the ion kinetic energy.

The acceleration dynamics of electrons in a laser wakefield accelerator is discussed, in particular the coupling of longitudinal and transverse motion. This coupling effect is important for electrons injected with a velocity below the laser pulse group velocity. It is found that the electron bunch is adiabatically focused during the acceleration and that a finite bunch width contributes to bunch lengthening and growth of energy spread. These results indicate the importance of a small emittance for the injected electron bunch.