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  • 1995-1999  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Optical dephasing on femtosecond time scales: Direct measurement and calculation from solvent spectral densities (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4027-4036 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The connection between dephasing of optical coherence and the measured spectral density of the pure solvent is made through measurements and calculations of photon echo signals. 2-pulse photon echo measurements of a cyanine dye in polar solvents are presented. Signals are recorded for both phase matched directions enabling accurate determination of the echo signal time shift. Echo signals are calculated by two approaches that employ the response function description of nonlinear spectroscopy; (i) a single Brownian oscillator line shape model, and (ii) the line shape obtained using the solvent spectral density. The strongly overdamped Brownian oscillator model incorporates only a single adjustable parameter while the experimental data present two fitting constraints. The second model incorporates the measured solvent spectral density. Both give very good agreement with the experimental results. The significance of the second method lies in this being a new approach to calculate nonlinear spectroscopic signals, for comparison with experimental data, that uses directly the measured spectrum of equilibrium fluctuations of the solvent. This approach also provides a better conceptual perspective for deriving insight into the nature of the solute–solvent coupling mechanism. Comparing the parameters for the strength of interaction in a variety of polar solvents it is found that the coupling involves the solvent polarizability and not the solvent polarity. The interaction mechanism cannot be deduced from the Brownian oscillator calculations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468531
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Explosive Nucleosynthesis Revisited: Yields (1995)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 33 (1995), S. 115-132 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.33.090195.000555
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Scaling supernova hydrodynamics to the laboratory : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2065-2071 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Supernova (SN) 1987A focused attention on the critical role of hydrodynamic instabilities in the evolution of supernovae. To test the modeling of these instabilities, we are developing laboratory experiments of hydrodynamic mixing under conditions relevant to supernovae. Initial results were reported in J. Kane et al. [Astrophys. J. 478, L75 (1997) and B. A. Remington et al., Phys. Plasmas 4, 1994 (1997)]. The Nova laser is used to generate a 10–15 Mbar shock at the interface of a two-layer planar target, which triggers perturbation growth due to the Richtmyer–Meshkov instability, and to the Rayleigh–Taylor instability as the interface decelerates. This resembles the hydrodynamics of the He-H interface of a Type II supernova at intermediate times, up to a few ×103 s. The scaling of hydrodynamics on microscopic laser scales to the SN-size scales is presented. The experiment is modeled using the hydrodynamics codes HYADES [J. T. Larson and S. M. Lane, J. Quant. Spect. Rad. Trans. 51, 179 (1994)] and CALE [R. T. Barton, Numerical Astrophysics (Jones and Bartlett, Boston, 1985), pp. 482–497], and the supernova code PROMETHEUS [P. R. Woodward and P. Collela, J. Comp. Phys. 54, 115 (1984)]. Results of the experiments and simulations are presented. Analysis of the spike-and-bubble velocities using potential flow theory and Ott thin-shell theory is presented, as well as a study of 2D versus 3D differences in perturbation growth at the He-H interface of SN 1987A.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873497
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  • 4
    Electronic Resource
    Electronic Resource
    Supernova hydrodynamics experiments on the Nova laser : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1994-2003 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In studying complex astrophysical phenomena such as supernovae, one does not have the luxury of setting up clean, well-controlled experiments in the universe to test the physics of current models and theories. Consequently, creating a surrogate environment to serve as an experimental astrophysics testbed would be highly beneficial. The existence of highly sophisticated, modern research lasers, developed largely as a result of the world-wide effort in inertial confinement fusion, opens a new potential for creating just such an experimental testbed utilizing well-controlled, well-diagnosed laser-produced plasmas. Two areas of physics critical to an understanding of supernovae are discussed that are amenable to supporting research on large lasers: (1) compressible nonlinear hydrodynamic mixing and (2) radiative shock hydrodynamics. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872341
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  • 5
    Electronic Resource
    Electronic Resource
    Solvent and frequency dependence of vibrational dephasing on femtosecond time-scales (1995)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 26 (1995), S. 535-551 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The results of degenerate wavenumber third-order polarization (pump-probe) measurements of vibrational dephasing and relaxation in a variety of solvents are reported. The 20 fs duration pulses are sufficiently short to allow the preparation and detection of vibrational coherences (i.e. wavepackets) to 800 cm-1 oscillator wavenumber. The high quality of the pump-probe data permits the unique determination of eight underdamped modes for the cyanine dye under study. The relaxation of the underdamped modes does not show a significant solvent dependence. The relaxation mechanisms that give rise to loss of vibrational coherence and to the solvent-dependent relaxation of low-wavenumber (〈100 cm-1) modes are discussed. The wavenumber dependence of the vibrational dephasing rate varies with a scaled exponential dependence exp(  - ω/ω0), or equally well with the inverse square of the vibrational wavenumber. The exponential form would imply that vibrational dephasing occurs by population relaxation. The latter form, however, may imply higher order coupling between the bath and solute through the solute vibrational anharmonicity such that the off-diagonal contributions to the prepared wavepacket relax by pure dephasing. Exponentially decaying contributions to the pump - probe signal are found to arise from overdamped modes that are excited by the short laser pulses as opposed to a solvation response. The solvent-dependent relaxation of these overdamped modes is determined to be similar to diffusive unimolecular barrier crossing dynamics observed in dense media.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250260709
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