Abstract
Impulsive stimulated scattering (ISS) is an entirely time-domain form of vibrational and quasielastic light scattering carried out on the femtosecond-picosecond-nanosecond time scales to complement conventional coherent and incoherent scattering spectroscopy in the THz-GHz-MHz frequency regimes. ISS permits direct observation of coherently vibrating species at various stages of vibrational distortion. This offers unique possibilities for measurement of vibrational dynamics, characterization of vibrationally distorted species, and observation of vibrationally induced rearrangements.1 Impulsive stimulated Brillouin and Raman scattering (ISBS, ISRS) have been used to excite coherent acoustic and optic phonons in crystals and to measure directly the dynamics of phonon-driven structural phase transitions in inorganic, organic, and incommensurate crystals. Femtosecond time-resolved observations of THz-frequency optic phonon oscillations and rapid (~1-ps) vibrational dephasing have been carried out through ISRS in inorganic crystals and in organic crystals with phonon-driven bimolecular reactions. Acoustic and orientational motions have been examined in viscoelastic fluids near liquid-glass transitions, liquid crystals, and simple fluids. ISRS measurement of vibrational population lifetimes ( T 1 ) and time-resolved absorption spectroscopy of coherently vibrating molecules and crystals are discussed. Finally, the ubiquitous occurrence of ISRS with ultrashort pulses is explained.1
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