Optical phase relaxation of impurity ions in a resonant radiation field

The kinetics of the electric polarization of a two-level center in the resonant field of laser radiation is described. The interaction with the reservoir inducing phase relaxation is simulated by the shift of the resonance frequency due to a multistep random process of arbitrary intensity. Explicit solutions of the integral equations describing the kinetics are obtained for seven different random processes. The conditions are found when the phase relaxation can be characterized by two times T2u and T2v which depend differently on the radiation intensity. On the basis of the microscopic theory a rigorous proof is presented of the Redfield hypothesis regarding the significant lengthening of the time T2u without any pronounced change in T2v in a resonant field whose amplitude (in energy units) is comparable to the amplitude of the local field inducing relaxation of the laser radiation was observed previously in an experiment on of free induction decay in Pr3+:LaF3