The multiphoton excitation of a polyatomic molecule by two infrared laser pulses is discussed. The infrared-active vibrational mode of the molecule is modeled as an anharmonic oscillator driven by two near-resonant coherent fields. The effects of intramolecular vibrational coupling, and other internal relaxation mechanisms are represented by suitable irreversible decay terms in the master equation describing the evolution of the molecular degrees of freedom of interest. The results show that, if the parameters of the excitation pulses are chosen properly, significantly higher molecular excitation can be obtained as compared with the single-laser-excitation scheme. Comparison with some recent experimental results shows that these calculations predict trends which are consistent with the available data.

• Received 3 March 1980

DOI:https://doi.org/10.1103/PhysRevA.22.261