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  • 1
    Digitale Medien
    Digitale Medien
    Stationary laser beam filaments in a semicollisional plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 441-444 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The cumulative effect of the ponderomotive force, inverse Bremsstrahlung heating and nonlocal electron thermal transport on the formation of steady state laser channels in an underdense weakly collisional plasma is studied for the first time. The nonlocal effects change both the distribution of the laser intensity and the density profile in the channel. Compared to the ponderomotive case, the addition of the nonlocal thermal effects results in density channels that are wider and deeper, and the power required for their formation is significantly decreased. The wide-spread density depletion wings of filaments created by nonlocal thermal effects can be important in the interaction of speckled laser beams with a plasma. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873827
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  • 2
    Digitale Medien
    Digitale Medien
    Nonlocal electron transport in laser heated plasmas (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2742-2753 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nonlocal theory of an electron transport in laser-produced plasmas with the large ion charge and arbitrary ratio of the characteristic spatial scale length to the electron mean free path has been developed for small potential perturbations. Closure relations have been derived from the solution to the electron Fokker–Planck equation which includes inverse bremsstrahlung heating and ponderomotive effects. All electron transport coefficients and their dependence on the laser intensity have been found. An expression for the electron heat flux includes laser field and plasma flow contributions. Identification of these different sources is necessary for the unique definition of the thermal transport coefficient which is independent of the particular application. A complete derivation of the potential part of the ponderomotive force in the presence of inverse bremsstrahlung heating has been presented. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872962
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  • 3
    Digitale Medien
    Digitale Medien
    Ion wave response to intense laser beams in underdense plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4333-4346 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Numerical and theoretical studies of laser beam interaction with underdense plasmas involving ion wave instabilities are presented. The theoretical model that is used involves realistic distribution of laser intensity in a focal spot and a non-paraxial electromagnetic wave equation coupled to the ion acoustic wave equation in a two-dimensional geometry. Included among the important results is a weak correlation between backscattered stimulated Brillouin scattering (SBS) reflectivity and filamentation or self-focusing instabilities. The transmitted light demonstrates angular spreading and frequency shifts consistent with near-forward SBS. The role of filamentation and self-focusing on the transmitted light is also discussed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872596
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  • 4
    Digitale Medien
    Digitale Medien
    Effect of the speckle self-focusing on the stationary stimulated Brillouin scattering reflectivity from a randomized laser beam in an inhomogeneous plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4369-4381 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effect of laser light self-focusing (SF) in speckles on stimulated Brillouin scattering (SBS) in an inhomogeneous plasma is studied. It is found that below but near critical power SF dramatically enhances the SBS reflectivity from an individual speckle, while above the critical power the pump power depletion due to SBS prevents strong SF and limits the maximum laser intensity in a speckle. The parameters that control the SBS/SF interplay are the ratio of plasma inhomogeneity scale length to the speckle length and the product of the plasma density and the speckle cross section. The consequences of the SF effect on the averaged SBS reflectivity of the randomized laser beam are revealed and their manifestations in recent SBS experiments with preformed plasmas are discussed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872599
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  • 5
    Digitale Medien
    Digitale Medien
    Saturation of backward stimulated Raman scattering and enhancement of laser light scattering in plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 256-273 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Theoretical and numerical calculations are performed using the system of Zakharov and electromagnetic wave equations, to describe the nonlinear behavior of stimulated Raman scattering (SRS) in a finite homogeneous plasma slab. The enhancement of secondary scattering processes due to the nonlinear SRS saturation is investigated. The parametric decay of the resonantly driven Langmuir wave provides a mechanism which saturates SRS and greatly broadens the Langmuir and ion acoustic wave spectra. These enhanced electrostatic fluctuations scatter the incident electromagnetic radiation. Scaling laws for enhanced Brillouin, forward Raman, and anti-Stokes forward and backward Raman scattering as well as criteria for their strong enhancement are given. The frequency spectra of enhanced Brillouin scattering shows red- and blue-shifted components, with different amplitudes depending on the plasma density and laser intensity. The numerical results have been compared with experimental data providing new or alternative explanations for the observations. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871446
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  • 6
    Digitale Medien
    Digitale Medien
    Plasma fluctuations driven by a randomized laser beam (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3002-3011 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nonthermal fluctuations produced by a randomized laser beam in an underdense plasma have been investigated in the regime of a nonlocal electron transport. A nonlocal closure to linearized fluid equations for fluctuating hydrodynamic variables properly accounts for inverse bremsstrahlung heating and ponderomotive force effects. It has been shown that a typical randomized laser beam as used in the inertial confinement fusion experiments can generate large amplitude density fluctuations well above thermal levels. An expression for the Thomson scattering cross-section from these fluctuations has been derived and discussed. The vortical velocity and magnetic field fluctuations can also be enhanced with the vortical plasma velocity reaching values comparable to the ion acoustic velocity. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873587
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  • 7
    Digitale Medien
    Digitale Medien
    Stimulated Brillouin and Raman scattering from a randomized laser beam in large inhomogeneous collisional plasmas. I. Experiment (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4659-4668 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experiments have been conducted at the LULI (Laboratoire pour l'Utilisation des Lasers Intenses) multibeam laser facility to study in detail stimulated Brillouin (SBS) and Raman (SRS) scattering from an intense (mean average intensity up to 1014 W/cm2) long (600 ps full width at half-maximum) laser beam interacting with thin exploded plastic foils. The plasmas are well characterized and the vacuum laser intensity distribution is well known due to using either random phase plates or polarization smoothing. Direct and simultaneous Thomson scattering measurements of the associated plasma waves allow us to obtain detailed information about the SBS and SRS temporal evolution and spatial localization. These data are being used to benchmark a statistical model of SBS and SRS from self-focused speckles. The results of this comparison will be presented in a companion paper. The analysis shows that both SBS and SRS are originated from self-focused speckles and reveals that plasma heating has an important effect on speckle self-focusing. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1312183
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  • 8
    Digitale Medien
    Digitale Medien
    Transverse electron susceptibility and the electromagnetic wave absorption in weakly collisional plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4205-4209 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A theory of plasma response to electromagnetic perturbations has been developed based on the full solution to the Fokker–Planck equation in high Z plasmas without electron–electron collisions. For the first time the transverse electron susceptibility has been calculated for the entire range of frequencies and wave numbers including the quantitative description of the weakly collisional regime where the wave frequency is comparable to the electron–ion collision frequency and the wave number is comparable to the inverse electron mean free path. The results have been compared to approximate expressions for the electron conductivity based on the Drude model showing discrepancy by a factor of few in regions where the spatial dispersion is important. The theory is applied to the calculation of laser light absorption in solid density plasmas. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872581
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  • 9
    Digitale Medien
    Digitale Medien
    Modeling of a stimulated Brillouin scattering experiment with statistical distribution of speckles (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3777-3785 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The results of experimental studies of stimulated Brillouin scattering (SBS) from a laser beam smoothed with a random phase plate (RPP) in a preformed expanding plasma are compared with the statistical theory of SBS from an inhomogeneous plasma. Many observed features can be explained assuming that SBS occurs in randomly distributed speckles. This hypothesis naturally combines observed pump depletion effects within a speckle, with relatively minor SBS reflectivity of the whole interaction beam. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871510
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  • 10
    Digitale Medien
    Digitale Medien
    Effect of diffraction on stimulated Brillouin scattering from a single laser hot spot (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3754-3760 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A single laser hot spot in an underdense plasma is represented as a focused Gaussian laser beam. Stimulated Brillouin scattering (SBS) from such a Gaussian beam with small f/numbers 2-4 has been studied in a three-dimensional slab geometry. It is shown that the SBS reflectivity from a single laser hot spot is much lower than that predicted by a simple three wave coupling model because of the diffraction of the scattered light from the spatially localized ion acoustic wave. SBS gain per one Rayleigh length of the incident laser beam is proposed as a quantitative measure of this effect. Diffraction-limited SBS from a randomized laser beam is also discussed. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871509
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