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.

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 pulses are focused in the interior of a human eye in areas of opacity to produce there an optical breakdown resulting in a high-temperature plasma, after which the filling up with liquid results in a transparent area. The empirically given limits for Q-switch laser pulses in the nanosecond range and for mode-locked pulses in the picosecond range are analyzed, and it is shown that these limits are below the self-focusing condition of laser beams in plasmas. A further analysis evaluates theoretically where the maximum limits are given in order to provide the parameters for the highest possible pulse energy that avoids damage in the eye by self-focusing.

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.

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.

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.

High inductive helical support provides a solution to controlling the alignment error of inner electrodes in magnetically insulated transmission lines (MITLs). Three-dimensional particle-in-cell simulations were performed to examine the current loss mechanism and the effects of structural parameters on electron flow in an MITL with a helical inductor. An empirical expression related to the ratio of electron current loss to anode current and the ratio of anode current to self-limited current was obtained. Electron current loss caused by helical inductor with different structures was displayed. The results indicate that the current loss in an MITL, near an inductive helical support, comprises both the inductor current and the electron current loss. The non-uniform structure and current of a helical inductor cause an abrupt change in the magnetic field near the helical support, which leads to anomalous behavior and current loss of electron flow. In addition, current loss in the inductive helical-supported MITL is negligible when the inductance of the support is sufficiently high. This work facilitates the estimation of electron current loss caused by the inductive helical support in MITLs.

This paper presents two-dimensional numerical simulations of heating of matter with intense heavy ion beams. It has been shown that it is very advantageous to irradiate the target with two different beams simultaneously, a main high intensity bunched beam of a heavy element like uranium and an unbunched low intensity beam of a lighter element like argon. The main beam is used to heat the target while the second beam is used as a diagnostic tool.

Influence of the shape of the focal spot on compression and heating of matter has also been studied using an elliptic focal spot with an ellipticity of 1.5 (semimajor axis is along y-axis and is 1.5 times the semiminor axis which is along x-axis). It has been found that the temporal behavior of the development of density, pressure, and temperature profiles along different directions is quite different, which is not the case with a circular focal spot.

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 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 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.

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.

We apply an Eulerian Vlasov code to study the amplification of an ultra-short seed pulse via stimulated Raman and Brillouin backscattering of energy from a long pump pulse, assumed at constant amplitude, in a plasma embedded in an external magnetic field. Detailed analysis of the spectra developed during the amplification process are presented, together with the evolution showing the pump depletion, accompanied by the counter-propagating seed-pulse amplification, compression and increased steepness of the waveform. In addition to the problem of the amplification of ultra-short seed pulses, there is an obvious academic interest in the study of problems of amplification of electromagnetic waves observed in many situations in laboratory plasmas and in the magnetosphere and other geophysical situations, such as in the environments of planets, where important variations in the presence and strength of magnetic fields are observed. The numerical code solves a one-dimensional relativistic Vlasov–Maxwell set of equations for a plasma in a magnetic field for both electrons and ions. We also apply the code to the problem of wakefield acceleration. The absence of noise in the Eulerian Vlasov code allows one to follow the evolution of the system with an accurate representation of the phase-space structures of the distribution functions.

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.

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.

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.

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.

Laser light trapping in cavities in near-critical density plasmas is studied by two-dimensional particle-in-cell simulation. The laser ponderomotive force can create in the plasma a vacuum cavity bounded by a thin overcritical-density wall. The laser light is self-consistently trapped as a half-cycle electromagnetic wave in the form of an oscillon-caviton structure until it is slowly depleted through interaction with the cavity wall. When the near-critical density plasma contains a preformed cavity, laser light can become a standing wave in the latter. The trapped light is characterized as multi-peak structure. The overdense plasma wall around the self-generated and preformed cavities induced by the laser ponderomotive force is found to be crucial for pulse trapping. Once this wall forms, the trapped pulse can hardly penetrate.

By the interaction of intense (1010 particles/500 ns) relativistic (∼300 MeV/amu) heavy ion beams with solid targets, large volumes (several cubic millimeters) of strongly coupled plasmas are produced at solid-state densities and temperatures of up to 1 eV, with relevance for equation-of-state (EOS) studies of matter at high energy density and heavy ion-beam-driven inertial confinement fusion (ICF). The time and space profile of the ion beams, focused by the plasma lens to diameters of a minimum of 0.5 mm in order to obtain specific energy depositions of up to about 4 kJ/g, were measured to calculate the energy deposition in the target. In the present work, the plasmas created by ion beam interaction with cryogenic gas crystals and metallic targets are studied, among other methods, by backlighting shadowgraphy and electrical conductivity measurements. The experiments are coupled with two-dimensional hydrodynamic simulations.

We consider the acceleration of electrons in vacuum by means of the circularly-polirized electromagnetic wave, propagating along a magnetic field. We show that the electron energy growth, when using ultra-short and ultra-intense laser pulses (1 ps, 1018 W/cm2, CO2 laser) in the presence of a magnetic field, may reach up to the value 2,1 GeV. The growth of the electron energy is shown to increase proportionally with the increase of the laser intensity and the initial energy of the electron. We find that for some direction of polarization of the wave, the acceleration of electrons does not depend on the initial phase of the electromagnetic wave. We estimate the laser intensity, necessary for the electron acceleration. In addition, we find the formation length of photon absorption by electrons, due to which one may choose the required region of the interaction of the electrons with the electromagnetic wave and magnetic field. We also show that as a result of acceleration of electrons in the vacuum by laser radiation in a magnetic field one may obtain electron beam with small energy spread of the order δε/ε ≤ 10−2.