The start of a new issue in a new year is always an opportunity to look back and to say thank you to the members of the editorial board and the editorial staff who made it possible that we were able to publish four interesting issues in Volume 24 last year. First of all, I want to thank the scientific community for submitting a large number of excellent original research papers to Laser and Particle Beams. In 2006, we were able to publish 71 articles plus editorial material and corrections. The average article in the journal is now 8–9 printed pages, and we have thus achieved the editorial goal to offer the community a place to publish their results without general space restrictions. Authors have accepted this opportunity to present their material with the necessary details. This seems to be very important to readers and authors as well, and we see that for a second consecutive year many articles in Laser and Particle Beams are referenced already during the first year, which is remarkable for a small journal with only four issues per year.

Various applications demand various kinds of ions. Charge state, energy and the amount of laser produced ions depend, primary, on the wavelength, the energy, the pulse duration, and the focusing ability of the laser used. Angle of the target irradiation, angle of the ion extraction (recording), and mainly the focus setting may significantly influence especially the portion of ions with the highest charge states. The participation of non-linear processes on the generation of ions with extremely high parameters is demonstrated. The observed effects support the idea of a longitudinal structure of the self-focused laser beam with a space period of ∼200 µm.

Los Alamos National Laboratory short pulse experiments have shown using various target cleaning techniques such that heavy ion beams of different charge states can be produced. Furthermore, by controlling the thickness of light ions on the rear of the target, monoenergetic ion pulses can be generated. The spectral shape of the accelerated particles can be controlled to yield a range of distributions, from Maxwellian to ones possessing a monoenergetic peak at high energy. The key lies in understanding and utilizing target surface chemistry. Careful monitoring and control of the surface properties and induction of reactions at different temperatures allows well defined source layers to be formed, which in turn lead to the desired energy spectra in the acceleration process. Theoretical considerations provide understanding of the process of monoenergetic ion production. In addition, numerical modeling has identified a new acceleration mechanism, the laser break-out afterburner that could potentially boost particle energies by up to two orders of magnitude for the same laser parameters. This mechanism may enable application of laser-accelerated ion beams to venues such as compact accelerators, tumor therapy, and ion fast ignition.

We report and discuss experimental results on the propagation of CPA pulses of moderately relativistic intensity in gas: they evidence the effects of the precursor pedestals of the main pulse. Details of great interest were observed for the first time with high quality femtosecond 90-degree interferometry. The interferometric data are also correlated with imaging and spectroscopy data of laser pulse transmitted through the gas. The most relevant physical features are confirmed by a numerical code which simulates the laser pulse propagation self-consistently with the ionization of the gas. We found that in this regime, the propagation of the intense femtosecond pulse is basically stable apart from very weak refractive effects. In order to allow propagation at fixed intensity along an optical path larger than the Rayleigh range, we performed a first successful attempt at producing hollow plasma channels able to guide the pulse.

The effects of radiation transport on nonlocal electron heat flow in high Z laser-produced plasmas is studied. Using a Fokker-Planck model for the electron heat flow, which is coupled to a radiation transport model, it is found that radiation transport strongly modifies electron heat transport at the critical surface and in the overdense regions for an aluminum plasma. It is concluded that, without radiation transport effects, the plasma temperature, as computed from Fokker-Planck models, is overestimated in the critical region and underestimated in the overdense region, for high-Z plasmas.

In order to enhance the power-load of two-cell stimulated Brillouin scattering (SBS) system, methods of using different media and mixed medium are proposed. In theory, the amplification function of two-cell system of different medium with close vicinity in the Brillouin frequency shift (BFS) is analyzed. Also the variation of BFS of the mixed medium with the mixing ratio is analyzed. In the two-cell SBS system pumped by Q-switched Nd:YAG laser, the SBS system performance characteristics are investigated with different media and mixed medium. The experimental results indicate that the Stokes can be sufficiently amplified by choosing different medium with close vicinity in the BFS; the power-load performance is enhanced as well as the maximum amplification efficiency the Stokes by choosing mixed medium.

This paper presents numerical simulations of thermodynamic and hydrodynamic response for solid targets that are irradiated with strongly bunched, highly focused, intense beams of energetic uranium ions. The main purpose of this work is to study the behavior of thermal stress waves induced in such targets by the incident ion beam. These theoretical studies will complement the experimental investigations that will be carried out in the near future at the Gesellschaft für Schwerionenforschung (GSI) plasma physics experimental area. These experiments will be performed using the existing heavy ion synchrotron, SIS18, which delivers 4 × 109 uranium ions in a single bunch with a length of about 125 ns. Other time structures, for example, a pulse that consists of a series of bunches, are also possible. The particle energy is on the order of 400 MeV/u and the beam can be focused to sub millimeter radius. This information concerning material response under intense beam loading will have important implications on designing a viable production target for the superconducting fragment separator, Super-FRS, which is going to be constructed at the future facility for antiproton and ion research (FAIR), Darmstadt, Germany, for the production and separation of exotic nuclei.

To investigate the influence of pulse repetition rate on the average size of the nanoparticles, nanocrystalline Si films were prepared by pulsed laser ablation in high-purity Ar gas with a pressure of 10 Pa at room temperature, under the pulse repetition rates between 1 and 40 Hz, using a nanosecond laser. Raman, X-ray diffraction spectra, and scanning electron microscopy images show that with increasing pulse repetition rate, the average size of the nanoparticles in the film first decreases and reach its minimum at 20 Hz, and then increases, which may be attributed to the nonlinear dynamics of the laser-ablative deposition. In our experiment conditions, the duration of the ambient restoration, a characteristic parameter being used to distinguish nonlinear or linear region, is about a few seconds from the order of magnitude, which is consistent with the previous experimental observation. More detailed model to explain quantitively the observed effect is under investigation.

This paper investigates the generation of plasma wave and third harmonic generation in hot collision less plasma by a Gaussian ultra intense laser beam, when relativistic and ponderomotive nonlinearities are operative. First, we derive the dynamical equation for the pump laser beam when these two nonlinearities are operative. The solution of pump laser beam has been obtained within the paraxial ray approximation. Filamentary structures of the laser beam are observed. On account of V→ × B→ force, the generation of plasma wave at second harmonic frequency has been studied in these filamentary structures. Interaction of the plasma wave with the incident laser beam generates the third harmonic. For the typical laser plasma parameters: Nd: YAG laser beam (λ = 1064 nm), ro = 15 µm, laser power flux equals 6 × 1017 W/cm2, electron density equals no = 1.9 × 1019 per cm3, the third harmonic yield comes out to be equals to 2 × 10−6.

Stimulated Brillouin scattering (SBS) and the laser-induced damage threshold (LIDT) in different multimode glass fibers with a core diameter of 200 μm are determined. Antireflective coatings for fiber end-faces with high LIDT are developed, which enhance the SBS reflectivity and reduce unwanted front-face reflections. The morphology of pump- and Stokes-radiation induced damages is investigated using atomic force microscopy.

The method of relativistic plasma control (RPC) for generation of single (sub-) attosecond pulses based on high harmonic generation at plasma surface is presented. Use is made of the concept of apparent reflection point (ARP), introduced for the sake of analytical treatment of the plasma dynamics. We show theoretically and numerically that managing the laser polarisation the ARP dynamics can be efficiently controlled and a single ultra-short pulse can be extracted out of the short pulse train generated by a multi-cycle driver. For the sake of future applications the structure of the pulse is studied analytically and numerically by particle-in-cell simulations.

This paper examines the necessity of including ion viscosity in modeling laser fusion implosions. Using the Naval Research Laboratory one-half Mega Joule laser fusion target as an example, it is shown that for virtually the entire implosion up to maximum compression, and the entire rebound after the implosion, ion viscosity is unimportant. However for about half a nanosecond before peak implosion, ion viscosity can have a significant, but by no means dominant effect on both the one-dimensional flow and on the Rayleigh-Taylor instability.

New extensions of the chirped pulse amplification (CPA) scheme designed specially for petawatt Ti:Sapphire lasers are considered. The two new schemes support a spectral bandwidth sufficient for 20 fs pulses and a temporal contrast of 1012. The Double CPA scheme consists of two CPA stages with an intermediate temporal pulse filtering for temporal contrast improvement. The scheme of Negative–Positive CPA amplification takes advantage of consecutive saturated amplification of down chirped and up chirped pulses. This allows a suppress imprint of gain narrowing, which usually limits the spectral bandwidth at the multi-terawatt power level, and reach the bandwidth in excess of 50 nm without using any direct spectral shaping of the pulse.

Intense laser-beam interactions with preformed plasma, preceding the laser-target interactions, significantly influence both the ion and X-ray generation. It is due to the laser pulse (its total length, the shape of the front edge, its background, the contrast, the radial homogeneity) as well as plasma (density, temperature) properties. Generation of the super fast (FF) ion groups is connected with a presence of non-linear processes. Saturated maximum of the charge states (independently on the laser intensity) is ascribed to the constant limit radius of the self-focused laser beam. Its longitudinal structure is considered as a possible explanation for the course of some experimental dependencies obtained.

New perspectives have been opened up in the field of laser–matter interactions due to recent advances in laser technology, leading to laser systems of high contrast and extreme intensity values, where the frontier of maximum intensity is pushed now to about 1022 W/cm2. Many striking phenomena such as laser-acceleration of electrons up to the GeV level, fast moving ions with kinetic energies of several 10s of MeV, as well as nuclear physics experiments have already actuated a broad variety of theoretical as well as experimental studies. Also highly relativistic effects like laser induced electron-positron pair production are under discussion. All these activities have considerably stimulated the progress in understanding the underlying physical processes and possible applications. This article reviews recent advances in the experimental techniques as well as the associated plasma dynamics studies at relativistic intensities performed at the Max-Born-Institute (MBI). Interactions of a laser pulse at intensities above 1019 W/cm2 with water- and heavy-water droplets, as well as, with thin foils are discussed. Rear and front side acceleration mechanisms, particle dynamics inside the dense target, proton source characteristics, strong modulations in proton and deuteron emission spectra, and finally generation of quasi-monoenergetic deuteron bursts are the topics covered in the article.

We present one-dimensional simulations performed using the multi group radiation hydro code MULTI with the goal of analyzing the target preheating effect under conditions similar to those of recent experiments aimed at studying the Equation of State (EOS) of various materials. In such experiments, aluminum is often used as reference material; therefore its behavior under strong shock compression and high-intensity laser irradiation (1013–1014 W/cm2) should be studied in detail. Our results reveal that at high laser irradiance, the laser energy available to induce shock pressure is reduced due to high X-rays generation. Simultaneously X-rays preheat the bulk of the reference material causing significant heating prior to shock propagation. Such effects induce deviations in shock propagation with respect to cold aluminum.