Self-focusing of Gaussian laser beam has been investigated in quantum plasma under the effect of applied axial magnetic field. The nonlinear differential equation has been derived for studying the variations in the beam-width parameter. The effect of initial plasma electron temperature and the axial magnetic field on self-focusing and normalized intensity are studied. Our investigation reveals that normalized intensity increases to tenfolds where quantum effects are dominant. The normalized intensity further increases to twelvefolds on increasing the magnetic field.

In this paper, a solid helical pulse-forming line (HPFL) is described. The electromagnetic (EM) dispersion theory is used to calculate the important parameters of the HPFL based on tape helix model. Dispersion effects on the important EM parameters of HPFL, such as electric length and characteristic impedances, are analyzed. When Al2O3 ceramic is applied to be the dielectric in the HPFL, the pulse width of the HPFL is calculated nearly 50 ns only with the length of 305 mm. EM field simulation can draw the dispersion curve of the HPFL directly, which can describe the dispersion effect on the electric length of HPFL. Furthermore, the EM field simulation and experiments are carried out to verify the theoretical calculations of the pulse wide and characteristic impedances. Both simulation and experimental results can prove the EM analyses and calculations in this paper.

We report and discuss experimental results on the propagation of CPA pulses of moderately relativistic intensity in gas: they evidence the effects of the precursor pedestals of the main pulse. Details of great interest were observed for the first time with high quality femtosecond 90-degree interferometry. The interferometric data are also correlated with imaging and spectroscopy data of laser pulse transmitted through the gas. The most relevant physical features are confirmed by a numerical code which simulates the laser pulse propagation self-consistently with the ionization of the gas. We found that in this regime, the propagation of the intense femtosecond pulse is basically stable apart from very weak refractive effects. In order to allow propagation at fixed intensity along an optical path larger than the Rayleigh range, we performed a first successful attempt at producing hollow plasma channels able to guide the pulse.

An Eulerian Vlasov code is applied for the numerical solution of the one-dimensional Vlasov–Poisson system of equations for electrons, and with ions forming an immobile background. We study the non-linear evolution of the bump-on-tail instability in the case when the system length L is greater than the wavelength λ of the unstable mode, with a beam density of 10% of the total density, nb = 0.1. We follow the growth and the saturation of an initially unstable wave perturbation, and the formation of a traveling Bernstein–Greene–Kruskal (BGK) mode, which evolves out of the instability. This first stage is followed by sidebands growing from round-off errors which develop and disrupt the BGK equilibrium. In the excited spectrum, mode coupling is mediated by the oscillating resonant particles and results in the electric energy of the system flowing to the longest wavelengths (inverse cascade), and reaching in the asymptotic state a steady state with constant amplitude oscillation modulated by the persistent oscillation of the trapped particles. Coherent phase-space electron holes are formed, which are localized phase-space regions of reduced density on trapped electron orbits, where the electron density is lower than the surrounding plasma electron density. The distribution function evolves to a shape with stationary inflection points of zero slope, at the phase velocities of the excited waves. The longest wavelengths show oscillations at frequencies below the plasma frequency, with phase velocities higher than that of the injected beam, which can accelerate electrons to energies in excess of the initial beam energy. The present work makes a connection between the formation of electron holes, the existence of inflection points of zero slopes in the electron distribution function at the phase velocities of the dominant waves, and at frequencies below the plasma frequency. A fine resolution grid is used in the Eulerian Vlasov code in the phase space and time to allow an accurate calculation of the time history of the system and of the dynamic and oscillation of the trapped particles in the low-density regions of the phase space, and of those particles at the separatrix regions of the vortex structures which evolve periodically between trapping and untrapping states and which can only be accurately studied using a fine-resolution phase-space grid.

A shock wave is a discontinuous surface that connects supersonic flow with subsonic flow. After a shock wave, flow velocity is reduced, and pressure and temperature increase; entropy especially increases across a shock wave. Therefore, flow is in nonequilibrium, and irreversible processes occur inside the shock layer. The thickness of a shock wave in neutral gas is of the order of the mean free path of the fluid particle. A shock wave also appears in magnetized plasma. Provided that when the plasma flow is parallel to the magnetic field, a shock wave appears if the governing equation for velocity potential is in hyperbolic type in relation with the Mach number and the Alfvén number. When the flow is perpendicular to the magnetic field, the Maxwell stress, in addition to the pressure, plays a role in the shock wave in plasma. When the plasma temperature is so high, as the plasma becomes collision-free, another type of shock wave appears. In a collision-free shock wave, gyromotions of electrons around the magnetic field lines cause the shock formation instead of collisions in a collision-dominant plasma or neutral gas. Regardless of a collision-dominant or collision-free shock wave, the fluid that passes through the shock wave is heated in addition to being compressed. In inertial confinement fusion, the fuel must be compressed. Really, implosion motion performs fuel compression. A shock wave, appearing in the process of implosion, compresses the fuel. The shock wave, however, heats the fuel more intensively, and it makes it difficult to compress the fuel further because high temperatures invite high pressure. Adiabatic compression of the fuel is the desired result during the implosion, without the formation of a shock wave.

The possibilities of surface plasma wave (SPW) on a metal-vacuum interface in semiconductor quantum plasma by considering the effects of Coulomb exchange (CE) interaction and the spin-polarization has been explored. The dispersion for the SPW has been setup using the modified quantum hydrodynamic (QHD) model taking into account the Fermi pressure, the quantum Bohm force, the CE, and the electron spin. The optical gain of SPW has been evaluated. It is found that CE effects and spin-polarization increases the wave frequency and enhances the gain during the stimulated emission.

We propose a new approach to the calculation of ion populations in the LTE dense plasmas in the superconfiguration approximation. The screening of plasma ions is obtained using the same free-electron chemical potential for each ion charge. This chemical potential is determined by iteration keeping the total density constant and varying the volume of each ion. In such a way our approach not only gives the charge neutrality of the plasma, but also assures that the free-electron density is equal in the vicinity of each ion. The resulting ion charge distribution is different with respect to the one obtained without imposing the constraint of equal chemical potential. For instance, the effective charge is a little bit higher, which can change the shape of the absorption spectra, especially at higher densities. Examples of absorption spectra of medium-Z plasmas in a temperature and density range close to the present opacity measurements are shown.

Highly ionized plasmas are being considered as a medium for charge neutralizing heavy ion beams in order to focus beyond the space-charge limit. Calculations suggest that plasma at a density of 1–100 times the ion beam density and at a length ∼0.1–2 m would be suitable for achieving a high level of charge neutralization. An Electron Cyclotron Resonance (ECR) source has been built at the Princeton Plasma Physics Laboratory (PPPL) to support a joint Neutralized Transport Experiment (NTX) at the Lawrence Berkeley National Laboratory (LBNL) to study ion beam neutralization with plasma. The ECR source operates at 13.6 MHz and with solenoid magnetic fields of 1–10 gauss. The goal is to operate the source at pressures ∼10−6 Torr at full ionization. The initial operation of the source has been at pressures of 10−4–10−1 Torr. Electron densities in the range of 108 to 1011 cm−3 have been achieved. Low-pressure operation is important to reduce ion beam ionization. A cusp magnetic field has been installed to improve radial confinement and reduce the field strength on the beam axis. In addition, axial confinement is believed to be important to achieve lower-pressure operation. To further improve breakdown at low pressure, a weak electron source will be placed near the end of the ECR source. This article also describes the wave damping mechanisms. At moderate pressures (> 1 mTorr), the wave damping is collisional, and at low pressures (< 1 mTorr) there is a distinct electron cyclotron resonance.

The influence of ponderomotive force-induced plasma motion on filamentation is examined, using both linear and non-linear descriptions. Although the time asymptote of the process is identical to the stationary convective amplification of filaments, the dynamics of the plasma response may have a serious impact on the transient behaviour of filamentation. The plasma motion contains large amplitude oscillations of inhomogeneities in the laser beam with maxima that substantially exceed the asymptotic value and temporary growth of the very narrow filaments, which cannot be amplified in the stationary approximation.

A couple of advanced techniques of high-efficiency pulse compression for KrF lasers have been developed in our laboratory. As is well known, electron beam-excited KrF lasers have a capability of large output energy of 100- to 1,000-ns pulse duration. However, high-efficiency operation under a short-pulse input is difficult to achieve because of the reaction kinetics and short lifetime of KrF excimers. For developing ultrahigh peak-power lasers, the efficient pulse compression of ns to ps and ps to fs pulses is essential. We demonstrated advanced techniques, Raman pulse compression in a transient Raman regime, and pulse compression in saturated amplifiers with saturable absorbers.

The interaction of femtosecond laser pulses with solid-state density plasmas in regime of normal skin effect is investigated by means of numerical simulation. For short-wavelength lasers and laser pulses with length ≲ 120 fs full width at half maximum, the regime of normal skin effect is shown to hold for peak intensities up to 1017 W/cm2. The basic characteristics of the interaction are revealed and certain departures from simplistic models in electron distribution function, in plasma dielectric constant, and in laser absorption are pointed out. Comparison with the published experimental results is made.

Collisionless shocks are shocks in which the mean-free path is much larger than the shock front. They are ubiquitous in astrophysics and the object of much current attention as they are known to be excellent particle accelerators that could be the key to the cosmic rays enigma. While the scenario leading to the formation of a fluid shock is well known, less is known about the formation of a collisionless shock. We present theoretical and numerical results on the formation of such shocks when two relativistic and symmetric plasma shells (pair or electron/proton) collide. As the two shells start to interpenetrate, the overlapping region turns Weibel unstable. A key concept is the one of trapping time τp, which is the time when the turbulence in the central region has grown enough to trap the incoming flow. For the pair case, this time is simply the saturation time of the Weibel instability. For the electron/proton case, the filaments resulting from the growth of the electronic and protonic Weibel instabilities, need to grow further for the trapping time to be reached. In either case, the shock formation time is 2τp in two-dimensional (2D), and 3τp in 3D. Our results are successfully checked by particle-in-cell simulations and may help designing experiments aiming at producing such shocks in the laboratory.

This paper deals with the analytical study of the effect of chirping of a laser pulse on its intensity profile, as it propagates in plasma. Considering a matched laser beam, graphical analysis of the intensity distribution across the chirped laser pulse and growth of modulation instability has been presented. Further, considering finite pulse effects to be a perturbation, the growth rate of modulation instability of the chirped laser pulse is evaluated and compared with that obtained due to an unchirped pulse.

This paper presents analytical calculations for terahertz (THz) radiation by beating of two cosh-Gaussian laser beams in a density rippled collisional magnetized plasma. Lasers beams exert a ponderomotive force on the electrons of plasma in beating frequency which generates THz waves. The magnetic field was considered parallel to the direction of lasers which leads to propagate right-hand circularly polarized or left-hand circularly polarized waves in the plasma depending on the phase matching conditions. Effects of collision frequency, decentered parameter of lasers and the magnetic field strength are analyzed for THz radiation generation. By the optimization of laser and plasma parameters, the efficiency of order 27% can be achieved.

Collective absorption, so far determined by numerical simulations, is explained in physical terms for cold and warm plasma. After deducing a few general relations for flat targets, interface phase mixing and nonadiabatic electron acceleration in the skin layer are identified as the main physical processes leading to irreversibility, that is, to absorption.

The plasma produced during pulsed-laser deposition of thin carbon films is studied in the presence of ambient gases (Air, He, Ar) at low and moderate irradiances of Nd:YAG laser. The presence of ambient gas shows a pronounced effect on the dynamics of the plasma plume. At moderate intensity, we report an appearance of a peculiar double-peak structure in the temporal profile of the C II transition in laser-produced carbon plasma as it expands into a background gas. We believe that the structure originates mainly due to stratification of the plasma into fast and slow ion components at the interface where Rayleigh-Taylor instability occurs. Thin carbon films deposited on silicon in the presence of argon gas have shown the characteristic features of diamond-like carbon in X-ray diffraction and Raman Spectroscopy. The X-ray diffraction pattern of carbon film deposited at 1 torr of argon gas pressure shows the dominance of (111), (220), (311), and (400) crystalline plane of cubic diamond.

An analytical and numerical study has been carried out for the generation of terahertz (THz) radiation by beating of two intense cosh-Gaussian laser beams (decentered Gaussian beams) in the rippled density magnetized plasma under the relativistic–ponderomotive regime. In this process, both laser beams exert a relativistic–ponderomotive force on plasma electrons at the beat frequency and impart them an oscillatory velocity in the presence of a static magnetic field. Due to coupling between this nonlinear oscillatory velocity with density ripple, nonlinear current is generated that excites the THz radiation at the different frequency. Higher-order paraxial-ray approximation (non-paraxial theory) has been used in this study. The effects of the decentered parameter, magnetic field, and density ripple on the THz radiation generation in ripple density magnetized plasma have been investigated. Further, the effect of beating of laser beams on the THz field amplitude and the efficiency of THz radiation have been studied. The amplitude and efficiency of the emitted radiation are found to be highly sensitive to the decentered parameter, magnetic field, and density ripple. It has been found that the amplitude and efficiency of the generated THz radiation increase significantly with increasing the values of decentered parameter, magnetic field, and density ripple.

The mathematical model for the propagation of intense laser pulse in a plasma having Gaussian profile is investigated. The model has been formulated considering that the relativistic–ponderomotive nonlinearity dominates over other nonlinearities in the plasma. Model equation for self-compression and self-focusing properties of the laser pulse has been set up and solved by both semi-analytical and numerical methods. The result indicates that due to the effect of group velocity dispersion, diffraction of the laser pulse and the nonlinearity of medium, the pulse width parameter as well as beam width parameter of pulse gets focused at a different normalized distance, and hence the normalized intensity is also deferred at those points. Numerical simulation shows an oscillatory behavior of intensity during propagation in the plasma either having minimum beam radius (r 0) or having minimum pulse duration (t 0) depending on the normalized distance.

Here, we report the generation of MeV alpha-particles from H-11B fusion initiated by laser-accelerated boron ions. Boron ions with maximum energy of 6 MeV and fluence of 109/MeV/sr@5 MeV were generated from 60 nm-thick self-supporting boron nanofoils irradiated by 1 J femtosecond pulses at an intensity of 1019 W/cm2. By bombarding secondary hydrogenous targets with the boron ions, 3 × 105/sr alpha-particles from H-11B fusion were registered, which is consistent with the theoretical yield calculated from the measured boron energy spectra. Our results demonstrated an alternative way toward ultrashort MeV alpha-particle sources employing compact femtosecond lasers. The ion acceleration and product measurement scheme are referential for the studies on the ion stopping power and cross section of the H-11B reaction in solid or plasma.

A NIF-type hohlraum target (Lindl 1995; CEA 1995) is analyzed in an integrated calculation that uses last revision (4.2) of MULTI2D code (Ramis et al. 1992). The numerical simulation includes: Lagrangian mesh, tracking of laser beams, inverse bremsstrahlung absorption, 3D radiation transport, radiation-induced hydrodynamics of casing and window panes, and radiatively driven capsule implosion. Electron heat conduction (Spitzer with flux limiter), tabulated Equations of State (Sesame), and LTE opacities are also included. Detailed results on hydrodynamic evolution of the system, compression symmetry, and energy balance are also provided.