The Research On Linear And Nonlinear Susceptibility In Four-level And Three-level Atomic Systems

The effect of atomic coherence has attracted much attention in quantum optics such as lasing without inversion, the enhancement of nonlinear process, the storage of pulse and laser cooling. The atomic coherences in four and three level systems are discussed in this thesis:1)Atomic coherence effects in four-level N-type atomic system are discussed. Compared with three-level atomic system, the atomic coherence effects in four-level can lead to EIT and EIA, which depend on the intensity of control light and the relaxation of the fourth level.2)We calculated theoretically nonlinear refractive index of a three-level A-type hot atomic coherence system inside an optical ring cavity. It showed that the refraction n2 is significantly enhanced and sharply changed when the conditions of atomic two-photon resonance are closed. The system is valuable in developing optical devices for the optical information process.