The pump wave reflected from the overdense plasma may play an important role in the dynamics of stimulated Brillouin scattering. The particular case of Double Stimulated Brillouin Scattering (DSBS) suggested by Zozulya, Silin, & Tikhonchuk [Sov. Phys. JETP 59, 756 (1984)] is studied here in detail. In DSBS the incident pump wave and the reflected pump wave scatter from a common ion acoustic wave. Some steady state properties of DSBS are reviewed. The analysis of DSBS dynamics is based on a series of ‘numerical experiments’.At small pump intensities the system asymptotically approaches a true steady state. When the intensity is increased the solution turns into a regular pulse train with intensity dependent period. Connections between the pulses and soliton-like solutions of a damped sine-Gordon equation are discussed.

The effect of long scale-length irradiation non-uniformities on the implosion of two different directly driven, gas filled shells (representative of large families of laser fusion targets) is studied by means of 2-D numerical fluid simulations. Quantitative results are given for parameters measuring the shell deformation and the azimuthal variation of the (density × radius) product (<ρR) as functions of the wavelength and of the amplitude of the irradiation non-uniformity. The reflection of the imploding shock wave is also qualitatively illustrated.

The paper presents experiments dealing with interaction of Nd-glass laser radiation with single and double planar Al foil targets. An ablatively accelerated thin foil may achieve high velocity which cannot be obtained in any other way (for the mass of the order of 10−7 g). It can be applied to investigate effects of collision between accelerated foil and planar metal target. The accelerated foil fragment may be regarded as a projectile. Craters arising in this way are similar to those obtained in hypervelocity impact (HVI) experiments. An additional comparison can be made with results of laser simulation method (LSM). The aim of our work was to find the scaling laws for the relative volumes of craters for the velocity range up to about 100 km/s. We should also like to compare results of both methods used by us: laser ablative acceleration method (LAAM) and laser simulation method with hypervelocity impact.

Spherically symmetric shock waves have been produced via Nd3+ laser induced break-down in helium, nitrogen and air at pressures ranging from 760 Torr to 2300 Torr. The measurements are performed at different absorbed laser energies (E0 = 0.05 J to 2 J) at the center of the experimental spherical glass cell where the breakdown of the gas takes place. The temporal evolution of the shock wave followed by a double-pulse, doublewavelength holographic technique is described hydrodynamically well by the point strong explosion theory. The ambient gas counterpressure plays a negligible role in determining the shock wave motion even at low laser energy absorption (E0 ≤, 0.5 J), whereas it has an appreciable effect on the gas density jump at the shock wave itself. The experimental data on temporal evolution of the density jump of the gas and the corresponding theoretical profiles obtained adopting a non-self-similar solution at the same laser absorbed energy are found to be in good mutual agreement.

The Spherical Pinch (SP) is a particular variation of the inertial confinement scheme, in that the two criteria required for plasma fusion breakeven condition, namely the attainment of a sufficiently high plasma temperature and of a product nτ in excess of 1014 cm-3. sec, are satisfied through two separate mechanisms. The advantage of this approach is that the scaling laws for breakeven are easier to satisfy than in the classical inertial confinement scheme. The first derivation of the scaling laws for spherical pinch experiments (Panarella & Savic 1983; Panarella 1987) was obtained under the simplifying assumption of an infinitely small central plasma in a sphere reaching the required high temperature for fusion, and of an undefined time delay Δt between the creation of such central plasma and the launching of the peripheral shock waves used to contain the central plasma. The analysis reported in this paper removes these assumptions and derives scaling laws which are generalized in their parameters, in that they explicitly contain the radius Rp of the central plasma and the time delay Δt.

We present some results of our opacity calculations for lead and gold at temperatures and densities relevant to ICF conditions. We use an average atom model based on the temperature dependent Thomas-Fermi shell approach. The absorption bands (broadening of lines) are accounted for with a simple T.F. fluctuation formula. The independent particle bound-bound, bound-free, and free-free photon cross-sections are taken without further approximations.

We report measurements of vacuum laser impulse coupling coefficients as large as 90 dyne/W, obtained with single μs-duration CO2 laser pulses incident on a volume-absorbing, cellulose-nitrate-based plastic. This result is the largest coupling coefficient yet reported at any wavelength for a simple, planar target in vacuum, and partly results from expenditure of internal chemical energy in this material. Enhanced coupling was also observed in several other target materials that are chemically passive, but absorb light in depth at 10-μm and 3-μm wavelengths. We discuss the physical distinctions between this important case and that of simple, planar surface absorbers [such as metals] which were studied in the same experimental series, in light of the predictions of a simple theoretical model. Ablation parameters for use with the model were determined in separate experiments near threshold in air and in vacuum. The transition from volume- to surface-absorption behavior in the infrared is described as being controlled by fluence-limiting and wavelength conversion in the uppermost target layer.

Fundamental parameters are studied for the detailed design of a picosecond high power KrF laser system. The saturation energy density of 2.3 mJ/cm2 and gain recovery time of 1.9 ns in an e-beam pumped KrF laser are observed. A 6 ps pulse is amplified to 1.9 J. The system at the Electrotechnical Laboratory is expected to deliver 10 ps pulses with total energy of several tens of joules in several beams.

Plasma creation occurs when the frequency of a tunable dye laser is adjusted to the 589 nm D-doublet of the sodium atom. Occurrence and Stark broadening of emission lines in the fluorescence light are used as diagnostics. The time history of the electron density and temperature is inferred from these measurements. The peak electron density was found to be above 5 · 1016 cm−3 with a temperature lower than 1 eV.

Aluminum sandwich foils can be compressed to more than twice the normal density by the use of shock waves generated by laser beams. We present calculations of the K-edge absorption structure of two fold compressed aluminum, and compare the results with experimental data. The atomic potential is calculated using a spherical band-structure model with Fermi-Dirac statistics for the electrons. The structure above the K-edge is calculated according to the Müller-Shaich formula for the propagating photo-electron. The mean free path of the electron is taken into account through a complex exchange correlation potential. An appropriate Debye-Waller factor is used to represent the effect of the relatively high temperature encountered in these experiments.

Hollow microcylinder targets, 200–300 μm in diameter, have been internally irradiated at up to 5 · 1014 W/cm2 with Nd:glass laser pulses directed through an axial entrance slit. The plasma evolution in the interior of the cavities was diagnosed with a pinhole imaging X-ray streak camera and a Nomarski-type interferometer. Plasma collision near the center of the cylinder is observed about 300 ps after the irradiating laser pulse. The experimental results are confirmed by a one-dimensional Eulerian fluid code.

A method of probing beam refraction is suggested for the investigation of laserproduced plasma with high density gradients. The refraction angle α of a probing ray as a function of ray impact parameter p is used as input data. Different experimental realizations of α(p) measurements are considered. Results from laser produced plasma interferograms processed with phase shift and refractometry methods are compared.

By focusing the TEA CO2 laser pulse onto a metal target in the vacuum cell, the backward jet of plasma produced by the laser pulse can create an electric pulse between the target and the cell wall. The effect of laser beam focusing parameter and vacuum condition on the conversion efficiency are investigated experimentally. The maximum output voltage is more than 300 V when the peak power density at the target surface is 1.4 × 109 W/cm2. The velocity of the plasma expansion is obtained by using separated collecting electrodes.

This paper gives the results of the investigations of four types of apodized (soft) apertures for beam shaping of UV, visible and IR high-power lasers with near-Gaussian and flat-top transmittance. The apodized apertures (AA) are ≈3–45 mm in diameter, but the principles of fabrication of such apertures lends the possibility of apodizing beams with diameter <1 mm and >200 mm. The examples of studies of the AA in high-power lasers are presented. The possibility of avoiding the Fresnel diffraction ripples is proved experimentally.

A Q-switched ruby laser, focussed by means of both gas and glass lenses, was used to irradiate massive planar carbon targets. Two different laser configurations were used, giving differing spatial beam qualities. Faraday cups positioned at various angles about the target were used to monitor ion flow properties of the resulting laser-produced plasmas. These flow properties were used to compare the laser-plasma producing characteristics of the lenses.