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  • 1
    Digitale Medien
    Digitale Medien
    Characterization of plasmas produced by laser–gas jet interaction (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3467-3472 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1379587
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  • 2
    Digitale Medien
    Digitale Medien
    Acceleration of injected electrons in a laser wakefield experiment (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2903-2913 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873248
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  • 3
    Digitale Medien
    Digitale Medien
    Characterization of electron beams produced by ultrashort (30 fs) laser pulses (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2605-2608 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1374584
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  • 4
    Digitale Medien
    Digitale Medien
    Strong self-focusing in quasi-stationary laser plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4259-4265 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1290594
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  • 5
    Digitale Medien
    Digitale Medien
    Stimulated Raman backscattering instability in short pulse laser interaction with helium gas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1682-1688 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871688
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  • 6
    Digitale Medien
    Digitale Medien
    Effects of pulse duration on self-focusing of ultra-short lasers in underdense plasmas (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 756-759 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An experiment investigating laser self-focusing in underdense plasmas is presented. It was shown experimentally that the critical power for relativistic self-focusing Pc is not the only relevant parameter, in particular when the laser pulse duration is comparable to plasma particle motion times: ωp−1 for electrons and ωpi−1 for ions. Using time resolved shadowgraphy, it was demonstrated that: (i) a pulse does not relativistically self-focus if its duration is too short compared to ωp−1, even in the case where the power is greater than Pc. This is due to defocusing by the longitudinal wake which is generated by the laser pulse itself. (ii) For pulses longer than ωpi−1, self-focusing can occur even for powers lower than Pc. This is due to the radial expansion of ions, creating a channel whose effect combines with relativistic focusing and helps the pulse to self-focus. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1447556
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  • 7
    Digitale Medien
    Digitale Medien
    Interaction of an ultra-intense laser pulse with a nonuniform preformed plasma (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3009-3016 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.874153
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  • 8
    Digitale Medien
    Digitale Medien
    Second harmonic generation and its interaction with relativistic plasma waves driven by forward Raman instability in underdense plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1127-1131 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872201
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  • 9
    Digitale Medien
    Digitale Medien
    Characterization of neutral density profile in a wide range of pressure of cylindrical pulsed gas jets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2329-2333 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1150619
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  • 10
    Digitale Medien
    Digitale Medien
    High density gas jet nozzle design for laser target production (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2961-2965 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The optimization of a cylindrical nozzle design to generate a uniform density profile for laser plasmas studies has been investigated using numerical simulations. In addition gas jet flows have been characterized using a Mach–Zehnder interferometer. The experimental results are in very good agreement with the simulation. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1380393
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