Electromagnetic radiation within the terahertz (THz) frequency range is of great interest for applications in remote sensing and time-domain spectroscopy. The laser-induced plasmas are promising mediums for generating THz radiation. It has been recently reported that focusing femtosecond Bessel pulses inside dielectrics induces a high aspect ratio over-critical plasmas. Here, we show that the intense resonantly driven electrostatic fields at the so-called critical surface lead to THz radiation emission. Through three-dimensional particle-in-cell simulation and analytical derivation, we have investigated the emission of THz radiation. We show that the THz radiation is associated with a hot population of electrons trapped in ambipolar electric fields of the double layers.

The creation of high-energy-density (≳106 joules per cm3) over-critical plasmas in a large volume has essential applications in the study of warm dense matter, being present in the hot cores of stars and planets. It was recently shown that femtosecond Bessel beams enable creating over-critical plasmas inside sapphire with sub-wavelength radius and several tens of micrometers in length. Here, the dependence of field structure and absorption mechanism on the plasma density transverse profile are investigated by performing self-consistent Particle-In-Cell (PIC) simulations. Two limiting cases are considered: one is a homogeneous step-like profile that can sustain plasmon formation, and the second is an inhomogeneous Gaussian profile, where resonance absorption occurs. Comparing experimental absorption measures to analytical predictions allows determining the plasma parameters used in PIC simulations. The PIC simulation results are in good agreement with experimental diagnostics of total absorption, near-field fluence distribution, and far-field radiation pattern. We show that in each case, an ambipolar field forms at the plasma surface due to the expansion of the hot electrons and that electron sound waves propagate into the over-critical region.

Second-harmonic emission at a frequency that is twice the laser frequency is an important diagnostic for nonlinear laser–plasma interaction. It is forbidden for centrosymmetric materials such as the bulk of sapphire. The symmetry, however, can be broken by dielectric discontinuities as a result of plasma generation inside a solid dielectric. In the present work, we explore the basic characteristics of experimentally observed second-harmonic emission during focusing a femtosecond Bessel beam inside sapphire. We employ three-dimensional particle-in-cell simulations and the Helmholtz wave equation for theoretical investigations. We analyze how the efficiency of second-harmonic generation and its polarization depend on the plasma parameters. We find that the second-harmonic is generated either due to the coalescence of two-surface electromagnetic waves or nonlinear interaction between the transverse electromagnetic wave and the longitudinal electron plasma wave driven by linear mode conversion. Experimental results agree with the theoretical predictions and confirm the existence of over-critical plasma inside the sapphire that is essential for the resonance of plasma waves or excitation of surface plasmons.

We demonstrate for the first time to our knowledge the generation of overcritical plasma densities inside transparent solids over long distances using femtosecond laser pulses. This opens new avenues for high energy density physics in confined geometry such as warm dense matter study or the synthesis of new material phases. We show both with experiments and first-principles simulations, that femtosecond conical interference via a Bessel beam creates a dense plasma rod with typically 100 nm diameter in sapphire. The interaction is in ideal conditions to trigger collisionless resonance absorption. This mechanism plays a primary role in the energy deposition process, yielding a plasma with an energy density on the order of MJ/cm3 and a length that can reach several cm using only tabletop femtosecond lasers.

With the advent of high intensity laser beams, solving the Maxwell equations with a free-dispersive algorithm is becoming essential. Several Maxwell solvers, implemented in Particle-In-Cell codes, have been proposed. We present here some of them by describing their computational stencil in two-dimensional geometry and defining their stability area as well as their numerical dispersion relation. Numerical simulations of Backward Raman amplification and laser wake-field are presented to compare these different solvers.

The collisional dynamics of a relativistic electron jet in a magnetized plasma are investigated within the framework of kinetic theory. The relativistic Fokker-Planck equation describing slowing down, pitch angle scattering, and cyclotron rotation is derived and solved. Based on the solution of this Fokker-Planck equation, an analytical formula for the root mean square spot size transverse to the magnetic field is derived and this result predicts a reduction in radial transport. Some comparisons with particle-in-cell simulation are made and confirm striking agreement between the theory and the simulation. For fast electron with 1 MeV typical kinetic energy interacting with a solid density hydrogen plasma, the energy deposition density in the transverse direction increases by a factor 2 for magnetic field of the order of 1 T. Along the magnetic field, the energy deposition profile is unaltered compared with the field-free case. c 2010 American Institute of Physics. [doi: 10.1063/1.3356066]

The paraxial propagation of a relativistic electron beam in a solid target is examined, within a three-dimensional model of particles interacting with the target electron return current via a diffusive electromagnetic field. Simulations of a modulated beam show amplification of the modulation seed, with growth rates comparing reasonably well with the linear analysis of the model. Scenarios of beam fragmentation are observed and discussed in more realistic conditions, when beam collisions on both target ions and electrons and the resulting solid heating and ionization are taken into account.

Both one-and-a-half and two-dimensional simulations of a dense neutral plasma impinged upon by a ultra-intense laser pulse are presented. The various scenarii of plasma interaction are reviewed.

A two-dimensional axisymmetric model of the propagation of intense femtosecond laser pulses through dispersion-free transparent media is described. The effects of diffraction, nonlinear Kerr effect (instantaneous and retarded) and multiphoton ionisation are included. Numerical results concerning air and other gases are discussed. In particular, time self-compression of femtosecond pulses is predicted. Stable self-guided pulses are simulated, in agreement with recent experimental observations.

Both one-and-a-half and two-dimensional relativistic particle-in-cell simulations of an overdense plasma impinged upon by an ultra-intense laser pulse are discussed. The results provide new features of the relativistic electron heating in relation with ion mobility and two-dimensional geometry.

Simulations of a linearly polarized laser wave in the range I(lambda) 2 is contained in (1018 - 5 multiplied by 1019) Wmicrometers 2/cm2 normally incident on a slightly overdense plasma have been performed with a 1.5 D relativistic particle-in-cell code. These kinetic simulations support the existence of relativistic self induced transparency, and complement past analytical work on the subject. Electron heating, laser absorption and ion motion are considered.

We present a numerical method to deal with the propagation of a short and highly intense laser pulse in an underdense plasma, leading to relativistic self-focusing and wakefield effect. By assuming that the temperature is low, enough and that there is no wave-breaking, we write hydrodynamic equations, coupled to Maxwell's equations. We treat them by a time splitting method, which stability is studied, and by a finite difference/volume method in space. A discrete version of Gauss' equation is preserved with time, so that no Poisson correction is needed. The code is consequently fully local and explicit. Results from two-dimensional simulations are presented.

Scattering of laser light by stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) is a concern for indirect drive inertial confinement fusion (ICF). The hohlraum designs for the National Ignition Facility (NIF) raise particular concerns due to the large scale and homogeneity of the plasmas within them. Experiments at Nova have studied laser–plasma interactions within large scale length plasmas that mimic many of the characteristics of the NIF hohlraum plasmas. Filamentation and scattering of laser light by SBS and SRS have been investigated as a function of beam smoothing and plasma conditions. Narrowly collimated SRS backscatter has been observed from low density, low-Z, plasmas, which are representative of the plasma filling most of the NIF hohlraum. SBS backscatter is found to occur in the high-Z plasma of gold ablated from the wall. Both SBS and SRS are observed to be at acceptable levels in experiments using smoothing by spectral dispersion (SSD).

By means of one-dimensional particle-in-cell simulations of an ultraintense electromagnetic wave normally incident on an overdense plasma, the transition from a regime of wave reflection to one of penetration is observed, when laser irradiance is increased. Both cases display Doppler-redshifted backscattered light originating from a moving surface. The irradiance threshold for the transition is given as a function of electron density. The energy reflected and the kinetic energies in both electrons and ions are provided.

The acceleration of electrons in the longitudinal electron plasma wave (EPW) created in the wake of an ultra-intense layer pulse is examined analytically. Our analysis is one-dimensional and assumes a square-shaped pulse which propagates in a well underdense plasma with the velocity of light in vacuum. Acceleration length and accelerated electron energies are predicted as a function of the EPW phase velocity and the laser irradiance. Comparison with electron acceleration in the usual sinusoidal EPW created by a low-intensity laser pulse is done.

Laser induced wakefields are investigated analytically and numerically. Wavebreaking limits are evaluated. In the case of resonant plasma acceleration wavebreaking restricts the number of useful pulses.