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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured and analyzed the second harmonic emission, both in the plane of the laser electric field and perpendicular to it, at several angles near 135° from the laser wave vector. The experiments used from 1 to 80 J of 1.053 μm light to irradiate carbon–hydrogen (CH) targets with a 550 ps pulse. A random phase plate was used, producing characteristic intensities in the range of 1013–1014 W/cm2. This was sufficient to drive the Ion Acoustic Decay Instability, producing Stokes emission well-separated from the emission spike at the second harmonic of the laser frequency. The spectral structure of the Stokes emission was qualitatively similar for all intensities and angles of observation. The duration of the signals showed trends anticipated from linear theory. To explain the scaling of the signal strength and spectral width requires nonlinear theory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1985-1996 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intensity scaling of stimulated Raman forward scattering has been measured in preformed laser-produced plasmas. It was found that predictions based on linear convective theory were consistent with the amount of scattered light measured when the laser intensity was less than about 1×1015 W/cm2. No increase in the amount of scattered light was found for higher intensities. The measured saturation level is compared to several nonlinear models: pump depletion, coupling to Langmuir and ion-acoustic waves, ponderomotive detuning, wave breaking, and particle trapping. It is found that saturation models based on ponderomotive detuning and on coupling to Langmuir and ion-acoustic waves are consistent with the experiment.
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  • 3
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The development of a plasma environment that is appropriate for the study of laser-plasma processes in laser-fusion plasma is reported. A material (titanium) with medium atomic number (Z) was used to provide x-ray measurements of radial and axial plasma symmetry as well as electron temperature. The electron density evolution was measured using stimulated scattering processes and odd half-harmonic generation from probe lasers of different wavelengths. The plasmas were created by two-sided irradiation of thin foils with 24 kJ of 351 nm laser light. When the peak electron density had decayed to about 4×1020 cm−3, the density profile was estimated to have a full width at half-maximum of 2 mm and the electron temperature was measured to be about 3 keV using K-shell spectroscopy. Two-dimensional computer simulations were found to reproduce some features of both electron density and temperature evolution. © 1995 American Institute of Physics.
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  • 4
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion plasma waves—purely electrostatic ion waves with a wavelength of order of the electron Debye length and frequency of the order of the ion plasma frequency—have long been known in theory but have proven difficult to detect experimentally. The difficulties stemmed from the techniques used to produce the plasma and to drive and detect the waves. In the work reported here, these problems were overcome by using resonant laser scattering to detect ion plasma waves in a multiply ionized, laser-produced plasma. This nonetheless required careful experimental design to minimize frequency smearing of the scattered signal by plasma gradients. The plasma was extensively characterized, allowing comparison of the theoretical dispersion relation with the wave data. The agreement of these two provides conclusive proof of the detection of ion plasma waves. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1473-1478 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the results of experiments designed to provide information regarding the scaling of the stimulated Raman scattering (SRS) instability in long-scale-length, inertial- confinement-fusion-reactor-size plasmas are described. Reactor-scale plasma conditions were experimentally simulated by exploding thin CH foils with nine beams of the Nova laser [Rev. Sci. Instrum. 57, 2101 (1986)]. Using a one-dimensional hydro model, the target and irradiation parameters were chosen to produce the largest-possible scale length plasma consistent with the energy and pulse width capabilities of Nova. The SRS emissions, driven by both the nine plasma-production beams and a tightly focused and delayed tenth beam, were recorded using an angularly resolved photodiode array and a temporally resolved optical spectrometer. These measurements verified the production of a reactor-size plasma (L/λ ≈ 5000) and indicated that the absolute levels of SRS backscatter detected in the present experiments have not increased relative to those measured in previous experiments despite a calculated sevenfold increase in the plasma density-gradient scale length. Inverse bremsstrahlung absorption of the scattered light is believed to be the dominant mechanism for this apparent saturation and, in this parameter regime, may enhance the effective thermal coupling between the incident laser and plasma densities below 0.15ncrit where absorption of the incident laser light is typically weak.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1282-1286 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Kinetic simulations illustrate some important nonlinear features of Raman and Brillouin backscattering. Steepening of the Brillouin-generated ion wave is observed and compared to theory. Examples of the rich competition between the Raman and Brillouin instabilities are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1089-1096 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experiment is reported in which several diagnostics were used to study the hydrodynamic expansion of exploding-foil targets. The CH targets, 1–3 μm thick, were irradiated with 3–4 kJ of 0.53 μm laser light in 1 nsec pulses. The electron density was diagnosed using the transmission and scattering of light at the laser frequency, the scattering of light at 3/2 of the laser frequency, the spectrum of Raman-scattered light, the x-ray spectrum from doped targets, and the image of the ultraviolet bremsstrahlung emission from the plasma. The measurements were consistent with one another, but generally were not consistent with two-dimensional computer simulations. The targets burned through later and took longer after burnthrough to reach quarter-critical density than predicted. This discrepancy may be a consequence of excessive profile steepening caused by the local, heat-transport model used in the simulation.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 372-374 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth of stimulated Raman backscattering (RBS) and forward scattering (RFS), as a function of density and temperature in a parabolic density profile, is examined and simulation results are compared to analytic theory. This work is relevant to the burnthrough foil experiments, in which Raman scattering is explored in spatial scale lengths long enough to be relevant to high gain targets.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3093-3096 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two-dimensional hydrodynamic simulations show that small diameter laser spots burn through flat foils considerably faster than larger spots. The physical mechanisms are (1) more nearly spherical divergence from the smaller spots which allows the debris to rapidly convect radially away from the small volume of laser heated plasma and (2) a variation on thermal self-focusing in which light is refracted into this volume, increasing the local heating rate.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 409-415 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Some aspects of multiple-wavelength interaction on solid targets have been experimentally studied at CO2-laser wavelengths with 1-nsec pulses. Contrary to predictions, the use of a two-line (10.6- and 9.6-μm) source does not reduce the back reflection. This result could be explained by a very short Brillouin interaction length or/and a very low saturation level. The hot-electron production is also not significantly modified by multiline illumination. A signal at the frequency sum indicates that, even at Iλ2 as low as 5×1013 W cm−2 μm2, the critical surface is not well defined and that both the 9.6- and 10.6-μm light interact in the same resonant zone. Finally, significant sidebands were measured at 8.7 and 12 μm. Some 1 (1)/(2) -dimensional simulations with mobile ions indicate that those sidebands probably originate from the beat frequency resonant density at 0.0123nc.
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