Mode-dependent dispersion in Raman line shapes: observation and implications from ultrafast Raman loss spectroscopy.
Ultrafast Raman loss spectroscopy (URLS) enables one to obtain the vibrational structural information of molecular systems including fluorescent materials. URLS, a nonlinear process analog to stimulated Raman gain, involves a narrow bandwidth picosecond Raman pump pulse and a femtosecond broadband white light continuum. Under nonresonant condition, the Raman response appears as a negative (loss) signal, whereas, on resonance with the electronic transition the line shape changes from a negative to a positive through a dispersive form. The intensities observed and thus, the Franck-Condon activity (coordinate dependent), are sensitive to the wavelength of the white light corresponding to a particular Raman frequency with respect to the Raman pump pulse wavelength, i.e., there is a mode-dependent response in URLS.
Umapathy
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Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India. umapathy@ipc.iisc.ernet.in
Mallick
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Lakshmanna
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