Experimental observations are reported on the interaction of 1-μm laser light with underdense plasmas (n ≤ 0·25 nc) from thin foil plastic targets. Nominal laser intensity on target was up to 3 × 1013 W/cm2 in a 3-ns pulse, but much higher intensity was reached due to spiky laser pulses. We studied forward-emitted second harmonic light as a diagnostic of the interaction and in particular of the occurrence of filamentation. Measurements included: energy monitoring of 2ω forward emission vs. target position and laser energy; time resolved (120-ps gate) imaging of the interaction region cross section. The second harmonic energy level was found to be sensitive to target position. In addition, the images obtained with the target in position of maximum second harmonic generation showed unstable structures whose scale length is comparable with the expected one for maximum filamentation growth. These results are shortly discussed in the framework of stationary filamentation theory and second harmonic generation in inhomogeneous media.

We develop a systematic comparison of thermodynamical and atomic properties computed within the three (TF, TFD, and TFDW) Thomas-Fermi modellings with results obtained from the average atom model. A special emphasis is placed on using the same analytic approximations for exchange, correlation, and gradient corrections. Analogies and discrepancies with respect to temperature behaviour are also stressed.

We studied X-ray emission from laser plasmas produced by irradiation of thin plastic foils with 1.064-μm Nd laser light at intensity up to 2 x 1013 W/cm2 with 3-ns pulses. The level of X-ray emission at different spectral windows was measured versus laser intensity and foil thickness. The electron temperature of the X-ray source was also measured. At intensity above 6 x 1012 W/cm2 our data showed the formation of nonthermal tails in the X-ray spectrum, which has been related to two plasmon decay instability.

Optically excited active medium at XeF(A)transition(λ = 481 nm) is considered from the viewpoint of its possible application in ultrashort (down to 10 fs) light pulses amplification due to the extremely wide amplification band of the transition. Photolytical pumping of XeF(C–A)by pulsed discharge or shock wave radiation allows one to amplify light beams with the cross-section at least upto ∼1 m2. Taking into account strong bulk and surface nonlinear effects at high-power density, it seemsfeasible to get the output energy up to ∼ 1 kJ and the power density in the focal spot up to 1023 W/cm2. Consideration of spatial-time distributionof the excited XeF(C) molecules, formed in the XeF;2 photodissociation wave under the action of powerful optical pumping, shows a possibility in principle to design multipass amplifiers with the inversion running wave, which are intended for the amplification of ultrashort pulsesup to the energies noted above.

A numerical and analytical estimation and a one-dimensionalhydrodynamic simulation show that a 30%reduction of the tritium content in a D-T pellet still gives sufficient energy output in aD-T inertial confinement fusion reactor.In other words, the tritiumb content can be reduced significantly without a significant reduction in the D-T fusion energy output.This new result also meansthat the tritium inventory can be reduced significantly before and during the reactor operation in the D-T inertial confinement fusion.This result comes from the contribution of a D-D reaction to the D-T reaction.

The knowledge of the properties of atoms in high-temperature/density plasmas is of deep interest in many fields of physics. Theoretical studies and interpretation of the inertial confinement fusion experiments is one of the examples. On the basis of the density functional formalism, a model of matter at extreme conditions is presented. Application of the model is illustrated by examples of average ionization state and equation of state calculations.

An experimental analysis is conducted to visualize sidescattered second harmonic spectra originating from the critical surface of a plasma produced from a 1, 064-nm laser beam. It is shown that longitudinal and transverse wave-scattering mechanisms producing the second harmonic may also alter the local plasma parameters. These irregular plasma parameter variations and the perturbed spatial uniformity of the incident laser beam can, in turn, be visualized through the second harmonic behavior. This work confirms the origin of the second harmonic production in an inhomogeneous plasma. Time evolution of the optical density of this harmonic showed spectral shifts due to the Doppler effect related to the critical surface dynamics. On the time-integrated spectra, shifted secondary peaks have been observed, indicating that the second harmonic takes its origin also from parametric decay as well as electron decay instability. Other properties of the interaction physics are deduced from the present second harmonic study.

The competition of stimulated Raman forward scattering and backscattering in a hightemperature, underdense, nearly homogeneous plasma slab is investigated. In such plasmas Landau damping limits the growth of the Raman backscattering, and the weaker forward process may reach comparable levels. A modest seeding of one of the scattered electromagnetic waves influences the competition to a large extent. The conversion of the pump wave to scattered waves is calculated. The simultaneous operation of the two processes can lead to considerable modifications in the electron distribution; e.g., two hot tail components are formed because the plasma waves involved have different phase velocities. The generation regions of the scattering processes are spatially separated. Consequently, a large number of thermal electrons can be accelerated to very high energies in two stages. The backward plasmons preaccelerate the electrons and the faster plasmons, excited in the forward scattering, operate as a booster.

The time-resolved X-ray emission recorded from a plasma produced by a Nd laser at high intensity (>1014 W/cm2) shows successive bursts. They are correlated with the pulsation of the back-scattered second harmonic spectrum obtained during the same shot. Both results show that the plasmons resonantly excited at the critical surface by the laser waves can undergo quasiperiodically the collapse process.

A new method for fabricating polystyrene ICF targets has been investigated. A solid solution of polystyrene (PS) containing a chemical blowing agent (CBA) is divided into small granules. These granules are blown into spherical shells in a vertical furnace. By varying the type and amount of CBA as well as furnace parameters, we have been able to produce PS shells 200–600 μm in diameter with wall thicknesses from 4–20 μm.

A scaling model for hot spherical ablative implosions in direct-drive mode is presented. The model results have been compared with experiments from LLE, ILE, and LLNL. Reduction of the neutron yield due to illumination nonuniformities is taken into account by the assumption that the neutron emission is cut off when the gas shock wave reflected off the center meets the incoming pusher, i.e., at a time when the probability of shell breakup is greatly enhanced. The main advantage of this semiempirical scaling model is that it elucidates the principal features of these simple implosions and permits one to estimate very quickly the performance of a high-aspect-ratio direct-drive target illuminated by short-wavelength laser light.

We propose a new formalism to electronic polarizability of dense, partially ionized plasmas. This formalism is based upon the density functional theory for the electronic equilibrium, the random phase approximation for the density response of electrons, and the cluster expansion in the averaging over ionic configurations. The first term in the final cluster expansion for the imaginary part of electron polarizability corresponds to the Lindhard dielectric function formula. The second term contains the electronic states of the average atom. The additional effects that result from this theory are: channel mixing (screening), “inverse Bremstrahlung” corrections, and free-bound electronic transitions. Our approach allows the plasma (collective) and atomic physics phenomena to be treated in the frame of one formalism. The theory can be applied for stopping power and opacity calculations.

For nonlocal thermodynamic equilibrium (LTE), the equations of state are not well defined and therefore the hydrodynamic equations are not applicable. In this case, the general transport equations (e.g., Boltzmann or Fokker–Planck) should be used. However, the coupling between atomic physics (rate equations) and the transport equations is extremely complicated. This article shows how the information given by the rate equations is translated into an effective potential. This “potential” theory is explicitly shown for two cases: lithium-like iron plasmas and aluminum plasmas. Moreover, it is suggested that the “collision terms,” and all other interactions that are not taken into account by the explicit rate equations, are described by a stochastic force given by a Langevin equation or equivalently by a Fokker-Planck equation in the ion density space.

The quasisteady expansion of a plasma ablated from a laser-irradiated pellet with classic (Spitzer) heat flux is reconsidered with a nonclassic heat flux law. The nonphysical flux factor (calculated flux vs. free streaming), going to infinity as one goes away from the pellet in the above transition regime, is corrected.

Laser-induced breakdown of argon gas near a metal surface is studied. It is observed that the threshold laser energy required to break down argon gas is reduced in the presence of a metal surface. Photoelectric emission from the metal surface dominates the thermionic emission to reduce the threshold laser energy for breakdown.

The results of experimental studies of the interactions between high-intensity 25-ps pulses from a neodymium laser and tenuous plasmas are reviewed. Electrons expelled laterally from the laser focus regions were observed to have energies of up to 1.5 keV and both the maximum electron energy and the measured electron energy spectra were found to be characteristic of acceleration by ponderomotive forces, which usually are the main part of the general nonlinear forces. These results confirmed the naive force theory and emphasized the major importance of nonlinear effects at high laser intensities.

Non-local thermodynamic equilibrium radiative transfer calculations have been performed to predict emission spectra from plasma heated by intense proton beams. Multilevel, steady-state atomic rate equations were solved self-consistently with the radiation field to determine excitation and ionization populations. Ion beam effects were, included in the rate equations. Proton-impact ionization cross sections were calculated using a plane wave Born approximation model with Hartree-Fock wave functions for the electrons. We examined the dependence of emission spectra on the temperature and thickness of the plasma. In addition, Kα satellite line spectra were computed to assess its potential as a temperature diagnostic. Calculated Kα spectral results are compared with recent Particle Beam Fusion Accelerator II experimental data.

In previous works, we developed several atomic physics models for calculating opacities for low-Z materials. In this work, we used those models for obtaining opacities for Au plasmas in local thermodynamic equilibrium. In this particular case, a great number of configurations must be considered for a full treatment of atoms at plasma conditions. Thus, we included several changes in the aforementioned models, which are extensively reported here.

A nonlinear theory of ion stopping in classical ideal plasmas is formulated on the basis of formalism of higher-order dielectric functions accounting for nonlinear relationship between polarisation and electric fields generated in plasma by the projectile ion. Corrections to the linear theory corresponding to the Barkas effect are evaluated explicitly. The result differs (what concerns the numerical coefficient) from that following from the harmonic oscillator model.

The main point of the hydrodynamic model of the electromagnetic field (Deng Ximing & Fang Honglie 1979, 1980) is that the motion of the electromagnetic field can be divided into two parts: orbital motion and intrinsic motion. This paper defines an intrinsic angular momentum deduced from the intrinsic motion and a related Î (imaginary number) operator, whose basic properties are discussed. In addition, the conservation property of the intrinsic angular momentum and the relation between it and the spin angular momentum of the electromagnetic field are described.