Showing papers by "Charles V. Shank published in 1992"
TL;DR: In this article, a time-dependent theory for femtosecond dynamic absorption spectroscopy is used to describe the creation and observation of molecular ground-state vibrational coherence through the resonance impulsive stimulated Raman mechanism.
Abstract: A time-dependent theory for femtosecond dynamic absorption spectroscopy is used to describe the creation and observation of molecular ground-state vibrational coherence through the resonance impulsive stimulated Raman mechanism. Model calculations show that the oscillatory absorption signal that arises from this ground-state coherence is maximized for a limited range of pulse lengths and that there is a complex relationship between the probe wavelength and the strength of the spectral oscillations. The generalized time-dependent linear susceptibility of the nonstationary system created by the impulsive pump pulse is defined and used to discuss the strong dependence of the measured signals on the properties of the probe pulse. Finally, calculations are presented to analyze the high-frequency oscillations ({approximately}20-fs period) recently observed in the transient absorption spectra of light-adapted bacteriorhodopsin (BR{sub 568}) following excitation with a 12-fs optical pulse. At the probe wavelengths used in this experiment, the contribution of stimulated emission is negligible at long times because of the extremely rapid excited-state isomerization; as a result, the spectral oscillations observed after this time are due to the impulsive excitation of coherent vibrations in the ground state. The transient response observed for BR{sub 568} is calculated using a 29-mode harmonic potential surface derived from amore » prior resonance Raman intensity analysis. Both the oscillatory signals and their dependence on the probe wavelength are satisfactorily reproduced. 68 refs., 11 figs.« less
211 citations
TL;DR: In this article, a 2.5 mu m-thick corona-poled copolymer film was used to double approximately 13fs-long, 50nJ-energy, 625nm-wavelength pulses at a 8-kHz repetition rate.
Abstract: A 2.5- mu m-thick corona-poled copolymer film was used to double approximately 13-fs-long, 50-nJ-energy, 625-nm-wavelength pulses at a 8-kHz repetition rate. The large effective d coefficient results in a relatively high conversion efficiency for such a thin film. A maximum efficiency of 0.13% has been measured. Long-term stable operation was obtained with efficiencies of 0.025% at the damage threshold of approximately 160 GW/cm/sup 2/. The damage threshold is remarkably high for organic materials and was found to be peak intensity rather than average intensity dependent. >
27 citations