The TRIDENT laser system at the Los Alamos National Laboratory is being used for fundamental experiments which study the interaction of self-focusing, stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in a near-diffraction-limited (single) laser hot spot in order to better understand the coupling between these plasma instabilities. The diffraction limited beam mimics a single hot spot found in speckle distributions that are typical of random or kinoform phase plates (RPP or KPP) used for spatial smoothing of laser beams. A long scale length, hot plasma (∼1 mm, ∼0.6 keV) is created by a separate heater beam, and the single hot spot beam is used to drive parametric instabilities. The focal plane distribution and wave-front of the interaction beam are characterized, and its intensity can be varied between 1014–1016 W/cm2. The plasma density, temperature, and flow profiles are measured using a gated imaging spectroscopy of collective Thomson scattering from the heater beam. Results of the laser and plasma characterization, and initial results of backscattered SRS, SBS, and beam steering in a flowing plasma are presented.

The editorial staff of Laser and Particle Beams (LPB) is pleased to continue in this issue the most successful tradition of publication of full papers from the internationally recognized conference series, the European Conference on Laser Interaction with Matter (ECLIM). Not all presentations at the conference are included, but a large portion of them are, based on the authors' willingness to submit the manuscripts for peer review.

The applicability of hydrodynamic models for theoretical description of UV laser ablation of polymers is studied. The plume formation is considered as a first-kind phase transition. In case of strongly absorbing polymers this phase transition occurs as a surface evaporation, and in case of weakly absorbing polymers as a bulk evaporation. The vapor plume is assumed to be transparent for laser radiation, and its expansion is described by the isoentropic hydrodynamic equations. New analytical expressions for ablation (etch) depths per pulse are obtained, which are in good agreement with the available experimental data (Afanasiev et al. 1997).

An analytical and numerical study of the stability of sheet electron beams in periodically cusped magnetic fields (PCM) is made. The beam has been considered as having edges with a prescribed density variation. In estimating the electrostatic fields, we have considered the density variation of both the edges along the width and thickness of the sheet beam. The conditions for beam focusing and beam matching are discussed.

The experiments to study the indirect drive targets' dynamics in a highly symmetrical X-radiation field were performed on the ISKRA-5 facility. This paper covered the results of experiments with the targets in the form of a Cu spherical hohlraum, the internal surface of which is coated with Au, with six holes for laser radiation input. In the center of the aforementioned hohlraum, a glass capsule filled with D–T gas was placed. In several experiments, the central capsule was coated with an ablator made of plastic with a different thickness. This allowed us to perform a series of experiments in which the different compression degree of D–T fuel was achieved. The analyses of experimental results revealed good agreement between the latter and the spherically symmetrical hydrodynamic calculations.

The penetration of the long-focused monochromatic radiation pulse into plasma whose density is much higher than critical has been modeled by simultaneous solution wave equation for the field and the gasdynamics equations for plasma in 2D axial symmetric case. The method and computation results are presented showing the effect of quasiwaveguide propagation of a pulse into plasma to a depth sufficiently exceeding the wavelength.

This issue of Laser and Particle Beams (LPB) includes only a portion of the more than 200 papers presented to the XXV European Conference on Laser Interaction with Matter (ECLIM), organized by the Frascati ICF Physics and Technology Laboratory of the Associazione EURATOM-ENEA, in Formia (Italy), on May 4-8, 1999.

Taking into account the stochastic excitation of the atoms (as quantum structures), we can suggest an absolutely new conception of a wide spectrum of processes in a femtosecond laser produced plasma. The electromagnetic fields being achieved with the modern laser technique exceed intraatomic fields by several orders. This fundamentally changes the physics of their interaction with the atomic structures. The atom effectively transforms the energy of radiation falling on it into fluxes on the nucleus. Quantum systems spin interaction with vector potential field being to play the essential role.

The precise measurements of the spectral line profiles near the short-wavelength limit of the Lyman series of Al are reported. The spatially resolved narrow-band spectra were attributed to macroscopic plasma parameters by using the results of 1D and 2D hydrodynamic plasma modeling. The gradual merging and broadening of the spectral lines Al Lyε–θ was compared to the synthetic spectra produced by atomic physics codes. The discrepancies between the experimental and theoretical data indicate the limits for applicability of standard theoretical models.

Two shells with the diameter of 0.8–0.9 mm and a wall thickness of ≅1 μm were produced at the Lebedev Physics Institute for the experiments conducted at the ISKRA-5 facility. The results of two experiments with the aforementioned shells conducted at the ISKRA-5 facility with the use of an indirect-drive set up. In one of the experiments, the diameter of the golden hohlraum was D = 2 mm while in the other it was D = 4 mm. In these experiments it was observed to be ≅4 times the difference of the average laser intensity on the hohlraum surface. The results of computational analysis of the experiments are also presented here.

Shock waves generated on eight meteorite and two Al targets by 5.4–5.6 J, 20-ns pulsed Nd:glass laser at 1054 nm generated peak pressures from 0.7 to 11 Gpa. The shock-induced particle velocities in the targets versus time was measured interferometrically. The target momentum coupling and mechanical momentum/energy coupling was highest for the Al. Among the meteorites the coupling was greatest for the Fe-Ni, which maintained physical integrity, and lowest for the stony meteorites, all of which disintegrated. Using particle velocity measurements, shock results are interpreted in terms of target fragmentation, inhomogeneity, and microstructural characteristics which are the dominant target parameters effecting energy and momentum coupling. Normalized values for the shocked material velocity and peak pressure in the targets compare favorably to similar experimental work on Al targets. Applications to modeling high-velocity meteoroid impact with planetary atmospheres, space debris remediation, and near-Earth object material interactions are discussed.

The inertial confinement fusion (ICF) research has remarkably developed in the last 10 years, which enables us to scope the fusion ignition and burn in the near future. Following the recent progress in the ICF, the perspectives of the inertial fusion energy (IFE) are presented. International collaboration is highly expected.

The experiments measuring the density of DT mixture compressed in indirect drive targets (X-ray targets) were conducted on the ISKRA-5 facility. The density was determined from the line broadening of H- and He-like Ar doped in DT-gas as a diagnostic substance. A series of three experiments with the X-ray targets having different shell thickness of capsule filled with DT + Ar mixture were carried out. In two of the three experiments, radiation spectra of Ar were recorded and the density of compressed gas was determined. The analysis of the experimental results for the X-ray target with a 280-μm diameter and a 7 μm wall thickness revealed that the density of the compressed gas may be estimated as ∼1 g/cm3.

A relativistically intense short laser pulse can produce a large flux of X rays through the interaction with electrons that are driven by its intense electromagnetic fields. Apart from X rays from the high-Z matter irradiation by an intense laser, two main processes, Larmor and Bremsstrahlung radiation, are among the most significant mechanisms for X-ray emission from short-pulse laser irradiation on low-Z matter in the regime of relativistic intensities. We evaluate the power, energy spectrum, brilliance, polarization, and time structure of these X rays. We suggest a few methods that significantly enhance the power of Larmor X rays. Because of the peakedness in the energy spectrum of Larmor X rays, Larmor X rays have important applications.

The National Ignition Facility (NIF) is a MJ-class glass laser-based facility funded by the Department of Energy which has achieved thermonuclear ignition and moderate gain as one of its main objectives. In the summer of 1998, the project was about 40% complete, and design and construction was on schedule and on cost. The NIF will start firing onto targets in 2001, and will achieve full energy in 2004. The Lawrence Livermore National Laboratory (LLNL) together with the Los Alamos National Laboratory (LANL) have the main responsibility for achieving X-ray driven ignition on the NIF. In the 1990s, a comprehensive series of experiments on Nova at LLNL, followed by recent experiments on the Omega laser at the University of Rochester, demonstrated confidence in understanding the physics of X-ray drive implosions. The same physics at equivalent scales is used in calculations to predict target performance on the NIF, giving credence to calculations of ignition on the NIF. An integrated program of work in preparing the NIF for X-ray driven ignition in about 2007, and the key issues being addressed on the current Inertial Confinement Fusion (ICF) facilities [(Nova, Omega, Z at Sandia National Laboratory (SNL) and NIKE at the Naval Research Laboratory (NRL)], are described.

The investigations of the influence of various types of wavefront distortions, varying in time, on the intensity distribution on the surface of a target are carried out. It is shown that distortions of a wavefront, equivalent to transverse displacement in time of a beam in far field at an angle of approximately 10 diffraction angles, results in practically full smoothing of a specl-structure of intensity distribution. Creation of phase distortions of a beam assigned as running in a cross section wave with an amplitude of more than 3 radian and with a spatial size exceeding 20–30 times the size of the kinoform phase plate element, permits us to reduce the depth of modulation in distribution of intensity in far field also. The capability of application is considered as a smoothing device of the dynamic plasma layer, based on the volume-structured medium. The model of energy transport process in such media is developed. Matching of calculation and experimental results is conducted.

Electromagnetic emission at the plasma frequency ωp and its harmonics nωp has been studied. Although such emission is well known from very low density plasmas (electron density of the order of ne ≈ 108 cm−3) now, for the first time it has also been observed from a high density plasma (electron density of the order of ne ≈ 1023 cm−3) produced by a high-intensity femtosecond laser pulse. This radiation is strongly connected to jets of high energy electrons produced in such steep gradient plasmas by collective mechanisms, and probably to nonlinear Langmuir waves in the overdense plasma region. Theoretical investigations using particle-in-cell simulations have been made to pinpoint the physical origin and properties of the emission. Preliminary results show a very weak scaling of the ωp and 2ωp emission with intensity, which should provide clues for future theoretical analyses. Although not the main subject of the present work, also harmonics up to the 20th of the laser fundamental may have been observed close to the ωp and 2ωp line emission in the present experiment (PACS numbers: 52.40.Nk, 42.65.ky, 52.65.-y, 33.20.Ni, 52.25.Qt).

A short review of the last 2 years of laser fusion activity at ISKRA-4 and ISKRA-5 facilities is presented. The main aim of the report is to describe the advantages of using spherical hohlraums for investigations of different types of implosions.

The first experiments to study the shell's controlled asymmetry of capsule with DT-fuel in a highly symmetrical X-ray field, which is obtained inside a spherical hohlraum, were implemented. The asymmetry results from the coating of one hemisphere with the additional layer of material. The main goal of the experiment was to define the value of the capsule asymmetry, allowing us to experimentally obtain the neutron yield, which would be very different from the yield obtained in the experiment with the spherically symmetrical shell having the same mass as the asymmetrical one. It was shown that the shell asymmetry of ∼50% leads to the ∼(2–4) times reduction of the neutron yield as compared with the symmetrical shell. 2D calculations of the asymmetric capsule compression, using the MIMOZA-ND code, were conducted. The calculations demonstrated that the compression of targets, when exploding pusher regime occurs has a complicated character. The computational neutron yield, and the delay of the neutron generation time are in good agreement with the experimental data.

We report the instrument description and the results of the laboratory calibration and tests of a mid-infrared tunable diode spectrometer for in situ trace gas concentration measurements in the stratosphere operating on a stratospheric aircraft. The spectrometer is dedicated to the measurement of the HNO3 amount in the stratospheric aerosols by means of gas-phase absorption spectroscopy on molecular roto-vibrational lines in the mid-infrared, using a tunable diode laser and a multipass absorption cell. The instrument was specifically designed for operation aboard of the stratospheric aircraft M55 Geophysica, in the frame of the Airborne Platform for Earth observation (APE) project. The instrument is part of a measurement package for the measurement of the chemical content of Polar Stratospheric Clouds (PSCs) and other atmospheric aerosols. This system can be also used as a stand-alone detector of molecular trace gases. Design criteria include an efficient optical layout, with a very low sensitivity to the vibration and thermal stresses and a very small footprint, and a detection scheme based on the sweep integration technique for fast data acquisition and high signal-to-noise (S/N) ratio. We report a new set of testing measurements on ammonia as the calibration gas with one order of magnitude improvement with respect to what we previously reported.