[en] The physics of relativistic laser plasma has renewed the interest in laser-plasma interaction in the recent past. Promising applications such as fast-ignitor for thermonuclear fusion, proton radiography, high energy particles and X-ray sources are foreseen. For a wide range application, it is required that a high intensity laser propagates over long distance, well in excess of the Rayleigh length. In the high intensity regime, electrons oscillate at relativistic velocities, which causes their mass to increase by the Lorentz factor. This effect has to be taken into account when defining plasma parameters relevant for the interaction. However, in laser plasma experiments, nonlinear self-focusing permits high intensity propagation over much longer distances and this happens when the laser power is greater than the critical power for relativistic self-focusing. When an ultra-intense laser pulse undergoes self-focusing in a plasma, one has to consider relativistic effects due to the mass increase of electrons oscillating in the laser field and charge displacement effects due to the ponderomotive radial expansion of electrons. Relativistic and ponderomotive self-focusing have been observed in many experiments and have proven to be an efficient way to guide a pulse over distance much larger than Rayleigh length. The self-guided propagation of a short pulse laser in magnetized plasma is based on the extraordinary mode propagation in magnetized plasma, with static magnetic field parallel to the oscillating magnetic field of the electromagnetic wave. Such a static magnetic field can be created by the pulse itself if the condition for ultrafast volume ionization are fulfilled. It is demonstrated that external magnetic field affects the channels, causing them to bend .These effect cast new light on the phenomena of self-focusing .They raise the possibility of combining the energy from several channels into one. Magnetic field is found to have a significant effect on overall propagation and plasma dynamics. (author)

[en] The temperature dependent normal state resistivity of single crystal K₃C₆₀ is analysed on the basis of Ziman's formula within Bloch-Boltzmann theory. Because of inherent intermolecular (low frequency) phonons (ω_er) as well as high frequency intramolecular phonons (ω_ra), the electron-phonon coupling constants are first deduced. The estimated contribution to electrical resistivity by considering both phonons i.e., ω_er and ω_ra, when subtracted from single crystal data implies a quadratic temperature dependence over most of the temperature range (20 K ≤ T ≤ 280 K). The quadratic temperature dependence of ρ [ρ_expt - {ρ₀ + ρ_e-ph}] is understood in terms of 3D electron-electron inelastic scattering. The comparison of single crystal experimental data appears favourable with the present analysis. (author)

[en] The relativistic oscillation of the mass of the electrons and also the relativistic electron ponderomotive force are shown to have a effect on the nonlinear propagation of intense electromagnetic waves. Based on WKB and paraxial ray theory, the steady state nonlinear refraction of relativistically intense, circularly polarized, Gaussian electromagnetic beams in an inhomogeneous plasma is studied. The nature of propagation of the beam depends on the power, width of the beam and 'Ω', the ratio of plasma and wave-frequency. It can be concluded from the calculations that electromagnetic waves can propagate in different regimes. The regions are steady divergence, oscillatory divergence and self-focusing. Numerical estimates are made for typical values of relativistic laser-plasma interaction process with electron density varying between 10¹⁷ -10²⁰ particles per cm ³ and radiation intensities in the range 10¹⁶ -10²⁰ W/cm ² for different plasma density ramp functions.

[en] For the intensities greater than 10¹⁸ W/cm ², circularly polarized radiation can propagate in electron plasma whose density is greater than the critical density. A strong flow of relativistic electrons, axially co-moving with the pulse arises. At this point the, the magnetic field of the electromagnetic wave becomes important. In the present paper, three regimes of propagation of circularly polarized laser beam in magnetized plasma are identified. An appropriate expression for the non-linear dielectric tensor has been used in the analysis under paraxial approximation. Two modes of propagation, viz, extraordinary mode and ordinary mode exist; because of the relativistic mechanism the induced magnetic field significantly affect the propagation of laser beam in plasma. Further studied for inhomogeneous plasma and penetration in overdense plasma is indicated. The induced magnetic field leads to the magnetically induced transparency due to extraordinary mode.

[en] In the present paper we make an analytical investigation to study transport properties with relativistic ponderomotive effect in two-electron temperature plasma. Using fluid model the two-electron temperature are introduced through relativistic ponderomotive force for the transportation of two species of electrons. Applying WKB and paraxial ray approximation the nonlinear dielectric constant and self-focusing equation is evaluated and analyzed with experimental relevance. Numerical calculations are made for different concentration of electron density (10¹⁹−10²¹ per cm³) at arbitrary values of laser intensity in the range 10¹⁸−10²¹ W/cm². For a minimum radius depending on the initial conditions it is oscillating between a minimum and maximum value. The hot electrons leading to the increase of the on-axis transportation and favorable effect on relativistic self-focusing

[en] Using a phenomenological lattice model incorporating the long-range Coulomb and charge transfer caused by the deformation of the electron shells of the overlapping ions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction, we present a comprehensive study to understand the effects of pressure on the elastic behavior as ductility (brittleness) and thermodynamical properties of Ga_1-xIn_xP. Estimated phase-transition pressure and the vast volume discontinuity in pressure-volume phase diagram confirm the structural phase transition from zinc blende (B3) to rock salt (B1) phase. From the elastic constants the Poisson's ratio ν, the ratio R_S/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and thermodynamical property Debye temperature is calculated. The Poisson's ratio ν and the ratio R_S/B allows one to conclude that Ga_1-xIn_xP is brittle in zinc blende (B3) and ductile nature is inferred in sodium chloride (B1) phase. To our knowledge this is the first quantitative theoretical prediction of the doping and pressure dependent elastic properties for mixed valent Ga_1-xIn_xP compounds and still awaits experimental confirmations.

[en] By formulating an effective interionic interaction potential that incorporates the long-range Coulomb, the covalency effects, the charge transfer caused by the deformation of the electron shells of the overlapping ions, the Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbour ions and the van der Waals (vdW) interaction, the pressure dependent elastic and thermodynamical properties of the III-V semiconductors as GaY (Y = N, P, As) are studied. The estimated values of phase transition pressure of GaY (Y = N, P, As) are in reasonably good agreement with the available data on the phase transition pressures (P_t = 41, 22, 17 GPa). The vast volume discontinuity in pressure-volume phase diagram identifies a structural phase transition from zinc-blende (B3) to rock salt (B1) structure. Later on, the Poisson's ratio ν, the ratio R_S/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic anisotropy parameter, elastic wave velocity, average wave velocity and Debye temperature as functions of pressure is calculated. From Poisson's ratio and the ratio R_S/B it is inferred that GaY (Y = N, P, As) is brittle [ductile] in zinc-blende (B3) [Sodium Chloride (B1)] phase. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of GaY compounds and still awaits experimental confirmations.

[en] By formulating an effective interionic interaction potential that incorporates the long-range Coulomb, the covalency effects, the charge transfer caused by the deformation of the electron shells of the overlapping ions, the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals (vdW) interaction, the pressure dependent elastic and thermodynamical properties of the III-V antimonide semiconductors as YSb (Y=B, Al, Ga, and In) are investigated. Estimated values of phase transition pressure of YSb antimonides are consistent with the available data on the phase transition pressures. The ratio R_S/B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and Debye temperature as functions of pressure is calculated. From the ratio R_S/B it is inferred that YSb (Y=Al, Ga, and In) are ductile and BSb is brittle in zinc blende (B3) phase. To our knowledge this is the first quantitative theoretical prediction of the ductile (brittle) nature of YSb antimonides and still awaits experimental confirmations.