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  • Articles  (88)
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  • Articles  (88)
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  • 1
    Electronic Resource
    Electronic Resource
    Meeting the challenge of detecting ion plasma waves (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2207-2215 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871243
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  • 2
    Electronic Resource
    Electronic Resource
    Measurements of the angular and temporal structure of second-harmonic emission from laser-produced plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3473-3483 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.871449
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  • 3
    Electronic Resource
    Electronic Resource
    Intensity scaling and saturation of stimulated Raman forward scattering (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1985-1996 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870654
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of titanium laser-produced plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3792-3803 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871079
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental studies of stimulated Raman scattering in reactor-size, laser-produced plasmas (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1473-1478 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859714
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear features of stimulated Brillouin and Raman scattering (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1282-1286 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858952
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  • 7
    Electronic Resource
    Electronic Resource
    Multiwavelength laser solid–target interaction at 10 microns (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 409-415 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865164
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  • 8
    Electronic Resource
    Electronic Resource
    Two-dimensional ray-trace calculations of thermal whole beam self-focusing (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 19-21 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal self-focusing of laser light may be significant when a plasma is irradiated with short-wavelength laser light. Self-focusing magnifies the light intensity which can increase absorption by plasma waves (producing hot electrons which may cause preheat), could increase scattering, and could be a perturbation source for the Rayleigh–Taylor instability. We use two-dimensional hydrodynamic simulations to characterize thermal self-focusing for parameters of interest to laser fusion applications, and present a simple model. A diverging beam is shown to reduce the self-focusing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865180
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  • 9
    Electronic Resource
    Electronic Resource
    Near-forward scattering of laser lightf| (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2596-2602 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Near-forward scattering of laser light in a plasma, in regimes relevant to future inertial-confinement-fusion (ICF) experiments, has been investigated experimentally. The intensity scaling of stimulated Raman scattering (SRS) forward scattering at one angle was measured from a low-Z plasma. It was found that the intensity threshold and scaling were consistent with convective theory. Forward SRS saturated at a relatively low intensity. In a second experiment using Ti plasmas, absolutely calibrated, time-resolved stimulated Brillouin scattering (SBS) spectra from up to seven different angles were measured simultaneously. It was found that the angular dependence of the scattered energy was qualitatively consistent with convective theory. The spectra provided the first evidence of near-forward SBS. Contrary to previous estimates, near-forward SBS was shown to be more efficient than oblique backscattering and may be an important effect for ICF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860696
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  • 10
    Electronic Resource
    Electronic Resource
    Superthermal electron production from hot underdense plasmas (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 3825-3831 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Very-high-energy electrons of up to an energy of ∼2.3 MeV have been observed to be emitted from the hot underdense exploding thin foil plasmas created by 10.6 μm CO2 laser radiation at intensity levels up to ∼4×1014 W/cm2. As a supplement to the electron measurements the forward and backward scattered light components were also measured. Correlation of these measurements shows that either Raman scattering or the high-temperature version of two-plasmon decay or both, manifesting themselves near the quarter-critical density region, are responsible for the production of a hot (Th∼135 keV) tail of electrons at least up to energies of 1 MeV. There are no indications that the Raman forward scattering (as distinct from Raman backward scattering) at lower densities plays any significant role. These experimental results are consistent with the results from a l 1/2 -dimensional particle-in-cell code simulation with a parabolic density profile resembling the experimental conditions. An apparent anomaly is discussed, which is that hot electrons are produced (both in experiments and simulations) at energies higher than the trapping value appropriate to electron plasma waves whose phase velocity is equal to the matching value (C/(3)1/2) at the turning point for the light of half the laser frequency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866420
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