Femtosecond spectrally dispersed three-pulse four-wave mixing: the role of sequence and chirp in controlling intramolecular dynamics

Abstract

The roles of pulse sequence and pulse chirp were explored using femtosecond three-pulse four-wave mixing (FWM), The experiments were carried out on gas-phase It and the degenerate laser pulses are resonant with the transition between the X ((1)Sigma g+) ground and B ((3)Pi(0u+)) excited electronic states. Impulsive excitation leads to the observation of vibrational coherence in the ground and the excited states. Control over the observed population and vibrational coherence is achieved by using specific pulse sequences. Using chirped pulses results in changes in vibrational coherence. When the PWM signal is spectrally dispersed, the two-dimensional data (wavelength and time delay) provide important spectroscopic information about the intramolecular dynamics of both electronic states. This information is not typically available in time or spectrally integrated measurements. A theoretical foundation for these observations based on the density matrix formalism is briefly discussed. Copyright (C) 2000 John Wiley and Sons, Ltd.