COHERENT PICOSECOND VIBRON POLARITONS AS PROBES OF VIBRATIONAL LIFETIMES

Picosecond pump-probe experiments on the C-O stretch vibration of acet ic acid in solution with infrared pulses from a free-electron laser ar e presented. We show that under typical experimental conditions of pul ses that are short compared to the inverse absorption linewidth and op tically thick samples (necessary to observe significant transmission c hanges), the experimental pump-probe data are strongly influenced by p ulse propagation effects (vibron polaritons) and coherent coupling bet ween pump and probe vibron polaritons. To extract the vibrational life time fi om the data, it is therefore necessary to perform a full simul ation of the propagation and coupling effects. (C) 1998 Elsevier Scien ce B.V.