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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4259-4265 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Collective Thomson scattering imaging has been used to study the propagation and self-focusing processes taking place during the interaction of a nanosecond laser beam with a preionized gas-jet plasma. The experiments have been carried out with a laser beam power PL exceeding greatly the critical power for ponderomotive self-focusing Pc. It has been found that the position of the ion acoustic waves excited by stimulated Brillouin scattering depends only weakly on the initial focal position of the interaction laser beam. These results, together with theoretical and numerical modeling, demonstrate that in such a regime (PL/Pc(very-much-greater-than)1) self-focusing is the dominant mechanism governing the localization of the interaction processes. © 2000 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2329-2333 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The neutral density profile of cylindrical gas jets is measured with a Mach–Zehnder interferometer under a wide range of backing pressures. The sensitivity of this diagnostic together with the mathematical treatment of the data allows us to measure neutral densities for argon gas as low as 1017 cm−3 for a 5 mm diam gas jet. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3009-3016 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of an ultra-intense laser pulse in a preformed plasma channel was investigated experimentally. Different regimes of propagation were observed when the pulse duration was varied. For a long pulse and powers lower than the critical power for self-focusing, PL/PC〈1 (I0=2×1017 W/cm2), the laser pulse was guided by the preformed plasma channel over three Rayleigh lengths (4 mm) and a longitudinal plasma wave was generated by envelope self-modulation of the pulse. For a short pulse and PL/PC(very-much-greater-than)1, the interaction was dominated by self-focusing and Raman instabilities. Numerical simulations were run for the latter case, giving results comparable to the experiment. The simulations were also used to investigate the dynamics of the instabilities at high power. They showed that strong Raman side scattering first occurs at the beginning of the interaction and is then followed by self-focusing and envelope self-modulation. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2903-2913 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron plasma wave (EPW) has been excited by a short laser pulse (5 J, 400 fs) via the laser wakefield (LWF) mechanism. At the LWF quasi-resonance condition, the 3 MeV injected electrons have been accelerated with a maximum energy gain of 1.5 MeV. The maximum longitudinal electric field is estimated to be 1.5 GV/m. It has been observed that electrons deflected during the interaction, can scatter on the walls of the experimental chamber and fake a high energy signal. A special effort has been given in the electron detection to separate the accelerated electrons signal from the background noise. The experimental data are confirmed with numerical simulations, demonstrating that the energy gain is affected by the EPW radial electric field. The duration of the EPW inferred by the number of accelerated electrons and by the numerical simulations is of the order of 1–10 ps. © 1999 American Institute of Physics.
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold ...
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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Particle accelerators are used in a wide variety of fields, ranging from medicine and biology to high-energy physics. The accelerating fields in conventional accelerators are limited to a few tens of MeV m-1, owing to material breakdown at the walls of the structure. Thus, ...
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1127-1131 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High conversion efficiency (0.1%) into second harmonic light generated in the interaction of a short-pulse intense laser with underdense plasma has been observed. In this experiment the plasma is created by optical field ionization of hydrogen or helium gas. Second harmonic spectra observed in the forward direction show Stokes and anti-Stokes satellites. This is due to the interaction of the second harmonic light with large-amplitude relativistic plasma waves. Second harmonic images taken at 30° from the propagation axis show that the radiation is generated over a length of a few times the Rayleigh length and that the origin of the second harmonic light is due to the radial electron density gradients created by the ionization process and the radial ponderomotive force. © 1997 American Institute of Physics.
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  • 8
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and theoretical results on the stimulated Raman backscattering (SRS) reflectivity of a short laser pulse (120 fs) interaction with an optically ionized helium gas are presented. The reflectivity is measured as a function of the gas pressure from 1 to 100 Torr. A monodimensional (1-D) theoretical model, including the refraction induced during the ionization process, describes the dependence of the SRS reflectivity with the gas pressure and explains its maximum at around 35 Torr. In the very low pressure case (〈15 Torr), the radial ponderomotive force expels the electrons out of the propagation region before the laser pulse reaches its peak intensity and significantly reduces the observed reflectivity. A 1-D hydrodynamic calculation, included in the model, describes this density depletion and a good agreement is obtained between theory and experiments in the whole range of pressures. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3467-3472 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experiment has been performed with one of the six nanosecond beams of the Laboratoire pour l'Utilisation des Lasers Intenses laser facility in order to create long scale uniform plasmas over a wide range of electron density (1×1019–1.6×1020 cm−3) and electron temperature (0.5–1.3 keV). Electron density and temperature evolution have been measured using Thomson scattering. Numerical simulations obtained by using a simple model are presented. Scaling law related electron density and electron temperature have been established in agreement with experimental data. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2605-2608 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed measurements of electron spectra and charges from the interaction of 10 Hz, 600 mJ laser pulses in the relativistic regime with a gas jet have been done over a wide range of intensities (1018–2×1019 W/cm2) and electron densities (1.5×1018–1.5×1020 cm−3), from the "classical laser wakefield regime" to the "self-modulated laser wakefield" regime. In the best case the maximum electron energy reaches 70 MeV. It increases at lower electron densities and higher laser intensities. A total charge of 8 nC was measured. The presented simulation results indicate that the electrons are accelerated mainly by relativistic plasma waves, and, to some extent, by direct laser acceleration. © 2001 American Institute of Physics.
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