Squeezing of the Molecular Vibrations by Femtosecond Laser Pulses

Abstract

In the last few years considerable interest was manifested to the stimulation of Franck-Condon transitions in molecules by ultrashort (femtosecond-range) laser pulses [1]. Since the spectrum of such a pulse definitely overlaps several vibrational levels, the molecule is put into a nonstationary vibrational state by the electron transition. This state represents a wave packet: a coherent superposition of vibrational eigenstates. In a number of papers [2-5] we studied how the properties of this wave packet relate to the characteristics of the laser pulse, i.e. to its duration and phase modulation. It was demonstrated that when the spectral width of the pulse is smaller than the width of the absorption band, but much larger than the frequency of vibrations, the vibrational ground state of the molecule transforms during excitation into a squeezed state with reduced value of the quantum uncertainty of the coordinate. All our previous results were obtained for Franck-Condon transition resulting exlusively from a spatial shift of harmonic nuclear potentials.