The coherent transient responses of two simple molecular liquids, CS2and CHBr3, are studied at room temperature with the technique of time-resolved pump/probe optical Kerr effect. Use is made of an ultrashort laser with pulsewidth varying from ≥ 100 to 28 femtoseconds (fs). For both liquids the instantaneous electronic response is found to increase markedly relative to the delayed nuclear response as input pulse is shortened. The contribution of the coherent coupling effect to the Kerr signal near delay zero is found to be significant, and is attributed to a retarded nuclear response. The latter, along with the nonvanishing response of nuclear motion to the shortest (28 fs) input pulse, strongly suggests that nuclei are intrinsically coupled to the valence electrons. The intrinsic electron-nucleus coupling in combination with molecular symmetry satisfactorily accounts for the observation that the ultrafast nuclear Kerr response of liquid CS2 is much stronger than the electronic one, whereas the opposite is true with liquid CHBr3. The ultrafast response of liquid CHBr3 also features the occurrence of vibrational quantum beats, involving as many as three normal vibrations of the CHBr3 molecule. The normal vibrations identified from the beats are the CBr3 symmetric deformation (υ + ̃3 = 222 cm-1) and the CBr3 symmetric stretch (υ + ̃2 = 540 cm-1), in addition to the CBr3 degenerate deformation (υ + ̃6 = 154 cm-1) observed in temporal domain heretofore. Both liquids also exhibit identical ultrafast intermolecular dynamics.
|Number of pages||13|
|Journal||IEEE Journal on Selected Topics in Quantum Electronics|
|Publication status||Published - 1996 Sept|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Electrical and Electronic Engineering