Physical Review A
A wide class of problems is considered involving the interaction of multilevel atoms with classical time-dependent fields switched on at a definite time. It is shown that the exact time-dependent Green's function can be written as the particular solution to an inhomogeneous differential equation involving derivatives with respect to the external field variables. Asymptotic expansions are discussed and analytic solutions found for several cases. The time and frequency distributions of radiation emitted by a field-perturbed atom are calculated by including the radiation field as a first-order perturbation. © 1975 The American Physical Society.
Drake, Gordon W. F. and Grimley, R. B.. (1975). Interaction of multilevel atoms with classical time-dependent fields. Physical Review A, 11 (5), 1614-1620.