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  • 1
    Electronic Resource
    Electronic Resource
    Relativistic and ponderomotive self-focusing of a laser beam in a radially inhomogeneous plasma. II. Beyond the paraxial approximation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 968-989 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation in a plasma of a high-intensity electromagnetic wave inducing both relativistic mass increase and ponderomotive expulsion of electrons is analyzed via two-dimensional simulations. The time/space evolution of the wave is modeled by an axisymmetric scalar wave equation in which the plasma frequency is an instantaneous and local function of the wave energy; the incident irradiance is assumed to be constant in time. The specific features of relativistic focusing are first discussed. The ponderomotive effect enforces the focusing process by expelling the plasma electrons, creating density bumps and sharp density gradient on the edge of the light beam; the nonlinear focusing is faster and stronger confirming the paraxial/Gaussian beam core analysis presented in Part I [Phys. Fluids B 5, 3539 (1993)]. In contrast to Part I, the light is guided in a sharp-edged density channel. The influence of the radial density inhomogeneity is then examined by using both convex (basin shape) and concave (bump shape) profiles. The self-focusing threshold power is increased for concave profiles. For convex profiles, the natural refraction helps the self-focusing observation but weakens the light-guiding trend previously observed. Finally, new features characterizing wave self-focusing, such as self-steepening and light reflection, are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870756
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  • 2
    Electronic Resource
    Electronic Resource
    Relativistic and ponderomotive self-focusing of a laser beam in a radially inhomogeneous plasma. I. Paraxial approximation (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3539-3550 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of a high-irradiance laser beam in a plasma whose optical index depends nonlinearly on the light intensity is investigated through both theoretical and numerical analyses. The nonlinear effects examined herein are the relativistic decrease of the plasma frequency and the ponderomotive expelling of the electrons. This paper is devoted to focusing and defocusing effects of a beam assumed to remain cylindrical and for a plasma supposed homogeneous along the propagation direction but radially inhomogeneous with a parabolic density profile. A two-parameter perturbation expansion is used; these two parameters, assumed small with respect to unity, are the ratio of the laser wavelength to the radial electric-field gradient length and the ratio of the plasma frequency to the laser frequency. The laser field is described in the context of a time envelope and spatial paraxial approximations. An analytical expression is provided for the critical beam power beyond which self-focusing appears; it depends strongly on the plasma inhomogeneity and suggests the plasma density tailoring in order to lower this critical power. The beam energy radius evolution is obtained as a function of the propagation distance by numerically solving the paraxial equation given by the two-parameter expansion. The relativistic mass variation is shown to dominate the ponderomotive effect. For strong laser fields, self-focusing saturates due to corrections of fourth order in the electric field involved by both contributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860828
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Unified treatment of the electronic structure of organic conjugated polymers (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 109-118 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical calculations for polaron-type defect structures on organic conjugated polymers are carried out by Green's function and transfer function formalism. Firstly, the renormalization concept is applied to mathematically convert the polymers PPP, PPY, and PTP to an equivalent (trans-PA)-like form. Then, it is shown that Green's functions and polaron wave functions are readily obtained from the equations for trans-PA by the appropriate substitution of the renormalized parameters. It is suggested that the existence of defects such as polarons or bipolarons could be invoked to provide a unified treatment of electric conduction in organic conjugated polymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300111
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    Paper (German National Licenses)
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