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P Michel,
C Labaune,
H C Bandulet,
K Lewis,
S Depierreux,
S Hulin, G Bonnaud,
V T Tikhonchuk,
S Weber,
G Riazuelo,
H A Baldis,
A Michard
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ABSTRACT: A strong reduction of the spatial coherence of a laser beam after its propagation through a plasma has been measured using a Fresnel biprism interferometer. The laser beam was diffraction limited; the coherence width was reduced from 40 mm in vacuum down to a few mm with the plasma. Numerical results based on a paraxial model exhibit a coherence degree close to the experimental one; they also prove the importance of taking into account the nonlocal transport effects in numerical simulations for such plasma conditions.
Physical Review Letters 05/2004; 92(17):175001. · 7.37 Impact Factor
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ABSTRACT: The stability and nonlinear evolution of a laser filament in an underdense, semicollisional plasma are studied with a simulation code accounting for the ponderomotive and thermal effects together with the nonlocal electron transport. It is found that the filament is stable at low intensities, where the trapped laser power is below the self-focusing threshold. For larger powers, the filament is unstable with respect to bending. This instability, though predicted in theory (the m = 1 mode), has not been seen so far in monospeckle modelling probably because of simulation symmetry. In our simulations an artificial noise source has been implemented in order to make nonsymmetric features appear. The instability leads to a complete breakup of the filament which reconstructs itself after some time and the process then repeats itself. Due to the filament instability the plasma sets in a regime of self-supported oscillations and results in temporal modulation and angular spreading of transmitted light. The numerical simulations are compared with theoretical predictions and experimental observations of speckle dynamics in the interaction of a randomized laser beam with preformed plasmas. © 2003 American Institute of Physics.
Physics of Plasmas 08/2003; 10(9):3545-3553. · 2.15 Impact Factor
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ABSTRACT: One-and-one-half-dimensional particle-in-cell (PIC) modeling with restored short-encounter collisional behavior is used to model the interaction of high-intensity short laser pulses with plasmas. The role of Coulomb collisions in expanding thin plasma targets at solid density is particularly investigated. It is shown that collisions play an important role for plasma expansion and ion acceleration mechanisms, even at high laser intensities. © 2001 American Institute of Physics.
Physics of Plasmas 01/2001; 8(2):387-390. · 2.15 Impact Factor
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ABSTRACT: Ultrashort pulse laser-solid interaction experiments with 4x10(16) W/cm(2),120 fs, 45 degrees incidence angle, p-polarized pulses are theoretically analyzed with the help of 1(1/2)-dimensional (1(1/2) D) particle-in-cell (PIC) simulations. The laser impinges upon preformed plasmas with a precisely controlled density-gradient scale-length. PIC electron distribution functions are used as an input to 3D Monte Carlo simulations to interpret measured electron distributions and Kalpha radiation emission. Satisfactory agreement between the experimental and simulation results is obtained for the measured absorption coefficient, the energy distribution of the back-scattered hot electrons, the hot-electron temperature in the bulk of the target, and the Kalpha yield, when the preplasma scale-length is varied.
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 09/1999; 60(2 Pt B):2209-17.
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ABSTRACT: The forthcoming laser installations related to inertial confinement fusion, Laser Mégajoule (LMJ) (France) and National Ignition Facility (NIF) (USA), require multidimensional numerical simulation tools for interpreting current experimental data and to perform predictive modeling for future experiments. Simulations of macroscopic plasma volumes of the order of 1 mm^3 and laser exposure times of the order of hundreds of picoseconds are necessary. We present recent developments in the PARAX code towards this goal. The laser field is treated in a standard paraxial approximation in three dimensions. The plasma response is described by single-fluid, two-temperature, fully nonlinear hydrodynamical equations in the plane transverse to the laser propagation axis. The code also accounts for the dominant nonlocal transport terms in spectral form originating from a linearized solution to the Fokker–Planck equation. The simulations of interest are hohlraum plasmas in the case of indirect drive or the plasma corona for direct drive. Recent experimental results on plasma-induced smoothing of RPP laser beams are used to validate the code.
Laser and Particle Beams.
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ABSTRACT: Simulations of ultraintense laser pulse-generated fast electron transport into solid-density matter are performed via a novel numerical code (PÂRIS) where both electromagnetic and collisional effects are taken into account. The code models self-consistently the response of the medium with locally varying ionization rate and electrical resistivity as functions of collisional and Joule heating. A variety of instabilities are seen to take place ranging from filamentation and coalescence to hollowing and hosing. Eventually, the ability of the fast electrons to heat solid-density matter along a collimated region is demonstrated. This heating is shown to be essentially due to the ohmic dissipation of the return current. These numerical results are of prime interest to explain the current fast ignitor-related experimental studies.
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ABSTRACT: The role of relativistic collisions in the framework of high-intensity laser-plasma interactions is investigated. Calculations show that the presence of relativistic collisions deeply affects the relaxation of the distribution functions, the density profiles and the absorption via inverse bremsstrahlung, even for high intensi- ties.
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ABSTRACT: Ultrashort pulse laser-solid interaction experiments with 4×1016 W/cm2,120 fs, 45° incidence angle, p-polarized pulses are theoretically analyzed with the help of 11/2-dimensional (11/2 D) particle-in-cell (PIC) simulations. The laser impinges upon preformed plasmas with a precisely controlled density-gradient scale-length. PIC electron distribution functions are used as an input to 3D Monte Carlo simulations to interpret measured electron distributions and Kα radiation emission. Satisfactory agreement between the experimental and simulation results is obtained for the measured absorption coefficient, the energy distribution of the back-scattered hot electrons, the hot-electron temperature in the bulk of the target, and the Kα yield, when the preplasma scale-length is varied.
Phys. Rev. E. 60(2).
