Band structure of stationary emission spectra from a three-level molecule pumped by strong radiation fields

A theory of the emission spectrum from a multilevel molecular system pumped by strong resonant radiation fields based on the double space theory of the density matrix is developed. We are especially concerned with a three-level, one-laser system, and a three-level, two-laser system. It is shown that the band structure cannot always be estimated by the energy level structure of the dressed states. In fact, in both model systems, triplet structures of the emission spectra can be observed in the case where the magnitude of the molecule-field interaction is larger than that of the detuning. The characteristic features of the band structure are interpreted in terms of the dressed state picture based on analytically solvable models. Several numerical calculations are performed to show how the multiplet band structure in the emission spectrum is influenced by the detuning and the power of the pump field(s).