Using the technique of tight-binding electron–ion dynamics, we have calculated the response of crystalline GaAs when a femtosecond laser pulse excites 1–20% of the valence electrons. Above a threshold fluence, which corresponds to promotion of about 12% of the valence electrons to the conduction band, the lattice is destabilized and the band gap collapses to zero. This result supports the conclusion that structural changes on a subpicosecond time scale observed in pump-probe experiments are of a nonthermal nature.

A three-term equation of state is used for the simulation of hydrodynamic shock phenomena. The reliability of it is tested by comparing the isotherms and shock Hugoniots obtained from it with available experimental data. This is illustrated for three typical materials Al, Pt and Au, which are of considerable interest for inertially confined thermonuclear fusion studies. We observe that reliable equation of state (EOS) data can be generated for nonmetallic substances like CH2. The EOS is used in the simulations of laser-driven shocks in double-layered target aluminum on gold (Al-Au) using hydrodynamic code employing a simplified laser-absorption model. The output from it is compared with the recent laser-driven shock experiments of Koeniget al.

Radiation characteristics of laser targets are studied in the soft X-ray region where photorecombination, bremsstrahlung and transitions in the discrete spectrum are the basic mechanisms of spectrum formation. The impact-radiational model is employed to describe the states of the laser target plasma. Characteristics obtained from the solution of the kinetic problem are used to compute absorption and emission coefficients. To set the time scale for a given field of gas-dynamic parameters, the transfer equation is solved and detailed information is obtained on the spectral composition of the outgoing radiation and its temporal evolution. Effective emission temperatures and radiation losses are determined. Integral radiation parameters are compared which have been derived from the solution of the transfer equation employing a volume luminescence approximation.

State of the art capabilities in soft X-ray lenses, multilayer mirrors, beamsplitters, and synthetically generated holograms are reviewed. Application of these capabilities in recent X-ray laser cavity experiments, and to the development of a soft X-ray interferometer and a high intensity (≥1013 watt/cm2) soft X-ray laser are discussed.

In this work construction characteristics and performance of a small scale self-heating copper vapor laser are presented. Analytical design of the thermal isolator is reported in some detail. Particular attention has been given to the knowledge of power deposition in the discharge to evaluate the component losses. In the optimized conditions the laser mean power is over 5 W, confirming the expected values. Details of the measurements on the system are also reported.

A diffraction limited focal spot is used to create a single speckle in a preformed plasma. The single speckle, or hot spot, is the simplest irreducible element for studying laser plasma interactions. Using the single hot spot configuration, the nonlinear behavior of SRS driven Langmuir waves has been investigated in both a fluid dominated and a kinetic regime. A transition between the two regimes has been observed as a function of kλD where k is the Langmuir wave-number and λD is the Debye length.

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.

A simple theoretical model is proposed for the interaction between two counter-propagating laser pulses (a pump and a seed pulse) in unmagnetized plasma. Pulse compression and amplification are observed via numerical simulation. A one dimensional fluid model for stimulated Raman backscattering is proposed to investigate the pulse compression and pulse amplification mechanisms. To accomplish this, energy is transferred from the long pump pulse to a seed pulse, with a Langmuir plasma wave mediating the transfer. The study focuses on the intensity profile of the pump laser pulse. A Gaussian and a ring intensity profile are, separately, considered for the pump laser pulse.

The low-impedance transit-time oscillator without foils is a new high-power microwave generator. In a previous report, a radiation power of 2.7 GW at 1.64 GHz has been achieved and the corresponding power conversion efficiency is 18.75%. Recently, the further experiments are continued in our laboratory. By increasing the cathode-anode gap properly, the operating voltage of device is enhanced to about 628 kV, and the corresponding radiation power reaches 3.6 GW. The device efficiency approaches 23%. In the newest experiments, because of the higher power level, the radiation power has been obviously influenced by RF breakdown in the vicinity of the dielectric window. By using a plastic bag filled with sulfur-hexafluoride (SF6), such an influence can be minimized.

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 current-neutralization fraction of a rotating and propagating light ion beam (LIB) injected into a low density plasma is investigated numerically. The beam space charge is essentially neutralized by a redistribution of the background plasma electrons in a time duration equal to the inverse of electron plasma frequency. When the density of the background plasma is comparable with that of the beam, incomplete current neutralization occurs because the strong magnetic field induced by the intense ion beam restricts the return plasma current.

In the simulation, the ion beam and the background plasma are treated as the fluids coupled with Maxwell's equations and Ohm's law, including the effect of the magnetic field on electrical conductivity. The calculations assume that the ion beam is injected in an unsteady fashion into the uniform plasma. It is found that the return current strongly depends on the density of the background plasma. The beam deceleration and the acceleration of the beam head and tail are also considered.

When a high power laser (1012 W/cm2) irradiates a target, it induces a shock wave, which reaches the (free) rear surface. The free surface is accelerated and the shock wave is back-reflected as a rarefaction wave. In the shock wave pressure regime involved here, melting of the target during the shock or during the rarefaction may occur. An optically recording velocity interferometric system (ORVIS) has been developed to measure the time evolution of the change in the reflectivity of the free surface. Shock waves of the order of hundreds of kilobars are produced in 50–125 μm thick Sn and Al foils, by a Nd:YAG laser system with a wavelength of 1.06 μm, pulse width of 7 ns (FWHM), and irradiance in the range (1.4–2.4)·1013 W/cm2. The changes in the reflectivity occur along two time scales: a slow one, more than 17 ns in Al and more than 30 ns in Sn, and a rapid one, less than 2.5 ns, in both materials. A possible explanation for the sharp decreases in the time scale is that melting occurs during the release of the free surface.

As a kind of flash heat source, intense pulsed ion beam (IPIB) can be used for material surface modification. The ablation effect has important influence on interaction between IPIB and material. Therefore, the understanding of ablation mechanism is of great significance to IPIB application. In this work, pure zinc targets were irradiated and ablated by IPIB. In the ablation process under the different ion beam energy densities, the ablation products were collected by a monocrystalline silicon substrate. By analyzing the ablation products with scanning electron microscope and energy-dispersive spectrometer, the surface morphology, and the spatial distribution of ablation products quantity were obtained. The results are useful for clearing the ablation process and the influence of beam parameter on the ablation effect.

A six-beam multiplexing master-oscillator-power-amplifier (MOPA) high power KrF excimer laser system has been built at CIAE for fundamental research on laser–plasma interaction. The MOPA system consists of front-end, two-stage KrF amplifiers (preamplifier and main amplifier) pumped by two-side electron beams, an optical angular multiplexing system, a synchronization trigger system, and a controlling-data acquisition system and some diagnostic systems. The total energy of the six-beam output from main amplifier on the target is 100 J/23 ns, the divergence of one beam is 0.2 mrad, the focal spot diameter is 220 μm, and the focal intensity on the target is 1013 W/cm2.

Compressed ion beams are being studied as a driver for inertial confinement fusion energy and for the creation of matter in the high-energy-density regime. In order to facilitate compression of a positive ion charge bunch longitudinally and transversely beyond the limit determined by the space-charge field of the bunch, a source of charge-neutralizing electrons must be provided. Plasma sources have been developed for the NDCX-I and NDCX-II experimental facilities, both for the 2-m-long, field-free drift regions, and for the small-diameter interior of the multi-Tesla final focus solenoid. Barium titanate based cylinders with a high dielectric coefficient are used to line the wall of the 2-m-long drift region and by applying a 9 kV pulse between the inner and outer surfaces of the cylinders, plasma with a density in the 1010 cm−3 range is formed. Results are presented from experiments using this plasma source on NDCX-I. A compact plasma source 5.1 cm long and 3.8 cm in diameter, also made using the barium titanate based material, has been developed for use in the bore of the final focus solenoid. Plasma generated near the wall of the plasma source will follow the fringing magnetic field lines of the solenoid and help to fill the bore of the magnet with plasma. Improved designs for the barium titanate plasma sources are being considered that use different inner-surface electrode materials and structures, and also use a modified electrical driver employing a spark gap crowbar switch. In addition, plasma source designs using so-called flashboard technology have been developed. In the flashboard plasma source, high density plasma is formed when the applied high voltage pulse causes a series of breakdowns between isolated copper patches aligned in rows along the surface of the 0.2 mm thick flashboard.

Filamentation is one of the most common nonlinear phenomena taking place in the laser–plasma interaction that splits the laser beam into high-intensity spikes. The present study deals with the nonlinear evolution of filamentation instability in laser–plasma interaction and the development of chaos in contrast to linear growth as reported by Kaw et al. in 1973. We have considered a non-uniform perturbation superimposed on plane-wave pump such that due to non-uniformity of the perturbation a finite intensity gradient arises and gives rise to ponderomotive force. This causes filamentation of wave, which has been studied presently using numerical methods as well as analytical tools. The results reveal that the intensity of perturbation gets localized and delocalized with the distance of propagation. The numerical simulation results also reveal that the intensity of perturbation route from ordered to chaotic behavior depending upon the pump laser and perturbation parameters. To study the chaotic behavior, Lyapunov exponents has also been calculated. The semi-analytical method is also developed to have an insight into some of the features of simulation like the formation of localized structures.

A theory based on the field and non-linearity expansions interms of Laguerre-Gauss functions is presented. The theoryi useful when very fast self focusing occurs, as in the case of relativistic self focusing. Results for self trapping with a saturable non-linearity are closer to the numerical results than those obtained by any other theory.

The results of numerical and analytical investigation of the ultra-intense laser pulse's interaction with overdense plasma are presented. The mechanisms of the wave field energy transformation into the overdense plasma energy are discussed. The effects of radiation propagation deep into plasma as well as long-living vortex formation, plasma boundary instability, and the surface structures formation are obtained. The basic mechanisms for the absorption of incident radiation and the role played by polarization of the radiation are studied. Nonlinear theory of plasma surface instability in the field of the strong electromagnetic wave is developed.

Numerical simulations of proton stopping lengths in aluminum slab plasmas have been done using a modified version of the MEDUSA-KA code and compared to other published computations. Simulations have been performed for proton beam parameters consistent with future experiments on the KALIF light ion accelerator at KfK including carbon contamination of the beam. These simulations show that proton range shortening should be evident in KALIF experiments and that the carbon contamination must be removed to allow interpretation of the data.

Coherent X rays can be produced by Compton scattering of laser light on a relativistic electron beam, whose current is periodically modulated by the same laser radiation in a suitable miniundulator. If electron and laser photon energy are properly matched, the modulated electron beam acts as a moving diffraction grating and the X rays show a high degree of coherence. A practical implementation of this scheme is shown.