Spatial Vortex Solitons In The Cold Atom Medium

Spatial vortex solitons have been developed from spatial solitons. For the characteristics of the vortex caused by wave-front dislocation and the topological charges associated with angular momentum, vortex solitons are different from simple spatial solitons. These features can take new utilizations of spatial solitons and greatly enrich nonlinear optics. Vortex solitons have been observed experimentally in many nonlinear optical media, some of which can be used in optical information, optical storage and optical computing. Most of the researches about optical vortex solitons are focused on media at room-temperature, only few on cold medium. Spatial vortex solitons in three-level cold-atom system with electromagnetically induced transparency (EIT) state were investigated in this paper by theoretical approximation and numerical simulation.In this thesis, the cold atomic medium was introduced firstly, then the techniques of electromagnetically induced transparency in three-level cold medium model with coherent interference coupling state were analyzed, and the optical effects of cold atomic medium were discussed. Consequently, a conclusion is drawn that cold atoms is a good medium for the research of nonlinear optics. Then, the research of spatial solitons was reviewed from equations of electromagnetic wave. The generation and stability of spatial dark and bright vortex solitons were also discussed as well as the analysis of the wave-front phase modulation of vortex soliton. The results show that there is possibility to study vortex solitons in cold medium.Based on lifetime-broadened three-level atomic model, spatial vortex solitons in cold atomic medium with EIT state were investigated in the fourth chapter. With appropriate parameters value selected, dark and bright spatial vortex solitons were obtained in cold medium by theoretical approximation and numerical simulation. Next, the stabilities of solitons were discussed by using micro-perturbation method with suitable experimental parameters, the results show that dark solitons are stronger than light solitons, though all are stable. The interactions of pair bright ring vortex solitons were investigated by using numerical simulation method, this investigation demonstrates that pair ring spatial vortex solitons can stably propagate in cold atomic medium.It can be concluded that suitable incident light can produce stable dark or light spatial vortex soltion in cold atomic medium. The cold atomic medium with EIT state is proved to be an excellent medium for the research of nonlinear optics, this characteristic is similar to superconductors in electromagnetism. It is believed that this work in three-level stair cold atoms model can provide new research opportunities in nonlinear optical experiments and help to promote new applications of related technology.