The Investigation Of Linear And Nonlinear Phenomenon In Coherent Atomic Medium

In the early development of nonlinear optics, it had been found that the strong nonlin-ear effect was obtained by weak incident light in the case of resonance. But the light would be absorbed by the media. So, the nonlinear effect was carried out by the non-resonant interaction between strong laser and media. The contradiction between resonance and absorption was settled after finding of the coherent atomic media [electromagnetically in-duced transparency (EIT) and active Raman gain (ARG) system]. The resonant absorption of light can be suppressed in EIT media. However, these was the function of gain in ARG system. Through these two system, the absorbtion was avoided and the strong nonlinear effect was realized in the weak light level.Based on these merits, we will study some physical characteristics about coherent atomic medium using multi-scale and numerical simulation method in this paper. We not only study the properties of the soliton and vortex, but also construct the party time symmetrical model and study its linear and nonlinear characteristics. This paper include:1. Study the characteristics of soliton and vortex in the five level M-type ARG system. Firstly, we obtain Maxwell-Bloch equation of five level ARG system according to the basic theory of interaction between gas atoms and light field; Secondly, a (2+1) dimensional Ginzburg Landau equation is shown through the method of multiple scales; Thirdly, the model is carried out, and dimensionality, nonlinear, dispersion and diffraction effects are controlled by detuning, pulse width, beam waist, the intensity of the control field and atomic density, and so on. We also obtain various types of two dimension soliton and vortex; Finally, the stabilities of solitons and vortices are analyzed.2. We not only realize PT symmetrical model based on EIT system, but also discuss its linear and nonlinear characteristics. The system whose external potential is provided by the assisted field and large-detuned laser field is consisted by a N-type coherent and its atomic media and large-detuned laser field. The probe field satisfies the nonlinear schrodinger equation, in which there is control Kerr nonlinear, diffraction term and PT symmetrical external potential. Based on this model, we obtain the linear spectrum and various types of solitons, and analyze their stabilities.