Role of multiphoton processes in four-photon scattering using high-intensity bichromatic pumping

A theoretical analysis is made of the action of high-intensity bichromatic pump radiation on a system of vibrational–rotational molecular levels. The effective Hamiltonian approximation is used to reduce the problem to the solution of kinetic equations for the density matrix with a periodic external perturbation. These can be solved by adopting a basis of quasienergy states. The Raman susceptibility profile is obtained and investigated for an isolated vibrational resonance. It is shown that any change in the polarizability under excitation can be determined from the dependence of the population difference on the pump and scattered radiation intensities.