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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7055-7057 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results on sound wave propagation in pulsed fields up to 50 T for CsCuCl3 and (VO)2P2O7. Sound velocity and attenuation exhibit anomalies at the field induced spin transitions at low temperatures. In CsCuCl3 we observe step-like anomalies in sound velocity and pronounced peaks in attenuation at the saturation field (34 T at 1.5 K) and broader anomalies at the commensurate-incommensurate transition (14–17 T). In (VO)2P2O7 we observe a strong anomaly at the critical field when the lowest triplet branch crosses the singlet ground state (27 T at 1.6 K). All these experiments give important information on the spin state in high magnetic fields of these low dimensional spin systems and on the spin-phonon coupling. © 2000 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)
    Journal of Applied Physics 91 (2002), S. 5545-5549 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present time and spectral resolved pump and probe studies of the intersubband dynamics in a bound to quasibound GaAs/AlGaAs quantum-well infrared photodetector dependent on the external electric field. Without bias, the excited electrons are scattered back to the ground subband with a time constant of about 2 ps. Subsequent intrasubband cooling is observed in the ground state, which gives rise to a relaxation component on a 50 ps time scale. With an applied electrical field, 35%–45% of the excited electrons escape to continuum states and are accelerated along the electrical field. Within time constants between 5 and 8 ps, the extended electrons are recaptured by wells in the low field bulk domain close to the collector contact. The redistribution of the carriers in the picosecond time regime and the screening of the external field due to the separation between electrons and donors leads to a change of the absorption spectrum for a time period shorter than the intrinsic response time of the electrical circuit.© 2002 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1368-1376 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational spectra of liquid nitrogen shock compressed to several high pressure/high temperature states were recorded using single-pulse multiplex coherent anti-Stokes Raman scattering. Vibrational frequencies, third-order susceptibility ratios, and linewidths are presented for the fundamental and several excited-state transitions. Vibrational frequencies were found to increase monotonically up to (approximate)17.5 GPa single shock and (approximate)30 GPa double shock. Above these pressures, the vibrational frequencies were observed to decrease with further increases in pressure. The decrease in vibrational frequency occurs in a pressure regime where the shocked nitrogen is becoming optically opaque. The consequence of the decrease in vibrational frequency on the Grüneisen mode gamma and its effect on the N2 equation of state is discussed. The transition intensity and linewidth data suggest that thermal equilibrium of the vibrational levels is attained in less than 10 ns at these high pressures and temperatures. Finally, the measured linewidths exhibit an almost linear dependence on shock temperature, and also suggest that the vibrational dephasing time has decreased to less than 1 ps at the highest pressures.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3488-3494 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single-pulse multiplex coherent anti-Stokes Raman scattering (CARS) was used to obtain vibrational spectra of 20%/80% liquid nitrogen/argon mixtures, shock compressed to several high-pressure/high-temperature states. A semiclassical model for CARS spectra was used to extract best fit vibrational frequencies, peak Raman susceptibilities, and Raman linewidths from the data. Up to a maximum single shock pressure of 17.1 GPa, the N2 vibrational frequency was found to increase monotonically with pressure. The vibrational frequencies measured in both the singly and doubly shocked N2/Ar mixtures correspond within experimental error to those for pure nitrogen at equivalent pressures and temperatures, implying that the influence of the interaction potential on the N2 vibrational frequency for the N2/Ar collision is not significantly different from that of a N2/N2 collision at these conditions. The transition intensity and linewidth data suggest that thermal equilibrium of the vibrational levels is attained in less than 10 ns at these shock pressures. Vibrational temperatures obtained were used to improve the potential function of argon used to calculate equation-of-state pressures and temperatures. The measured linewidths suggest that the nitrogen vibrational dephasing time decreased to about 1 ps at the highest pressure shock state.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1261-1263 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Γ2–Xz1 intersubband dynamics in GaAs/AlAs quantum-well structures is investigated by time-resolved infrared pump and probe experiments. In the studied structure, the second Γ level in GaAs is nearly resonant to the first Xz level in AlAs, resulting in elastic Γ–X scattering. A biexponential behavior of ground-state recovery has been found with a time constant in the order of 1 ps for the Γ2–Γ1 relaxation and a time constant of 7 ps (at 10 K), which represents the Xz–Γ2 transfer. © 2001 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique for quantitative analysis of gas mixtures in a laser mass spectrometer is presented. It is based on the addition of two calibration gases with different orders of multiphoton ionization process to the sample gas. The ratio of the signals of these two internal standards serves as a sensor for the laser intensity within the ionization volume. Thus strongly fluctuating signals due to higher-order multiphoton ionization can be normalized for every single laser shot. In addition, for such a relative measurement, effects of long-term drifts of the apparatus are eliminated. Concentrations varying from a few ppm to several percent could be determined with an accuracy better than 10% at every single laser shot. Therefore this technique allows high time resolution.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coherent anti-Stokes Raman scattering (CARS) and spontaneous Raman spectroscopy have been used to obtain vibrational spectra of shock-compressed and static high-pressure fluid nitrogen, respectively. Vibrational frequencies were obtained from the CARS data using a semiclassical model for these spectra. Spontaneous Raman vibrational frequencies were determined by fitting data using a Lorentz-shape line. A functional form was found for the dependence of the vibrational frequency on pressure and temperature to 40 GPa and 5000 K, respectively. By fitting the vibrational data to this form, a pressure scale based on the fluid nitrogen vibron has been calibrated for use at very high temperature. The nitrogen vibron pressure scale was used to determine the fluid-δ nitrogen phase boundary up to 20 GPa and 900 K.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9379-9388 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational spectra of liquid nitrogen/carbon monoxide mixtures, shock compressed to several high-pressure/high-temperature states, were obtained using single-pulse multiplex coherent anti-Stokes Raman scattering (CARS). The experimental spectra were compared to synthetic spectra calculated with a semiclassical model for CARS intensities and using best fit vibrational frequencies, peak Raman susceptibilities, and Raman linewidths. Up to a maximum shock pressure of 9.3 GPa, both the N2 and CO vibrational frequencies were found to increase monotonically with pressure but depended strongly on the nitrogen/carbon monoxide mixture ratio. An empirical fit of the Raman frequency shifts incorporating previously published neat nitrogen and carbon monoxide data, using a functional form dependent on pressure, temperature, and mixture ratio, accurately describes both the N2 and CO shifts. The transition intensity and linewidth data suggest that thermal equilibrium of the vibrational levels is attained in less than 10 ns at these shock pressures and the vibrational temperatures obtained were used to improve the potential function used to calculate equation-of-state pressures and temperatures. The measured linewidths were different for N2 and CO and suggest that the vibrational dephasing time decreased to a few ps at the highest pressure shock state.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5603-5608 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational spectra of liquid carbon monoxide shock compressed to several high pressure/high temperature states were recorded using single-pulse multiplex coherent anti-Stokes Raman scattering. Vibrational frequencies, third-order suceptibility ratios, and linewidths are reported for the fundamental and first excited-state transition. The observed vibrational frequency shift with shock pressure was substantially less than that observed previously in nitrogen, implying a significant difference in the details of their inter- and intramolecular potentials. The transition intensity and linewidth data suggest that thermal equilibrium of the vibrational levels is attained in less than 10 ns at these shock pressures, and the vibrational temperatures obtained are comparable to calculated equation-of-state temperatures. The measured linewidths suggest that the vibrational dephasing time decreased to ∼2 ps at our highest pressure shock state.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6765-6771 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational spectra of liquid oxygen, shock compressed to several high-pressure/high-temperature states, were obtained using single-pulse multiplex coherent anti-stokes Raman scattering (CARS). The experimental spectra were compared to synthetic spectra calculated using a semiclassical model for the CARS intensities and best fit vibrational frequencies, peak Raman susceptibilities, and Raman linewidths. Up to the maximum shock pressure of 9.6 GPa, the vibrational frequencies were found to increase monotonically with pressure. An empirical fit, which could be used as a pressure/temperature/frequency calibration standard, showed that the Raman frequency shifts could be accurately described by linear pressure and temperature dependences. Above ≈9 GPa, the liquid oxygen opacity at 632.8 nm increased rapidly, presumably because of proximity (collision)-induced absorption. Calculations showed that the induced absorption did not resonantly enhance the CARS spectra, but did attenuate the laser beams and the CARS signals. The measured linewidths suggest that the vibrational dephasing time decreased to approximately 1 ps at the highest pressures.
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