Investigation Of Nonlinear Polarization Dynamics In Coherent Atomic Media

Since the invention of laser,nonlinear optics has attracted a great attention and has been widely used.Nonlinear optical phenomena in the process of interaction between light and matter are one of the most important research topics in nonlinear optics.For a long time,in order to obtain a strong nonlinear optical effect,people mainly study the far-off-resonant interaction between a strong laser field and a medium,named strong light nonlinear optics.In recent years,the discovery and study of electromagnetically induced transparency(EIT)have provided the possibility of achieving strong nonlinear optical effects under weak light conditions in resonant media(i.e.weak light nonlinear optics).In particular,EIT technology provides a favorable platform to study the effects of quantum optics,precision measurement,and weak light nonlinearity.The EIT eliminates the absorption of the probe laser field by the resonant medium through the quantum interference effect induced by the external control laser field.In addition,EIT can also significantly enhance the nonlinear optical susceptibility of the medium and significantly change its dispersion properties,resulting in strong nonlinear optical effects and slowdown of the group velocity of the probe field.In recent years,studies on weak light nonlinear optical effects in EIT media have been carried out successively(eg.transient optical response characteristics of EIT media,high-efficiency multi-wave mixing using EIT,ultraslow weak optical solitons in EIT media,and so on.).However,the polarization dynamics of the probe field in EIT media has not been studied in depth.The related physical theories still need further exploration and improvement.In this,the polarization dynamics of weak light in coherent atomic media has been studied by using resonance nonlinear multiple-scales method and numerical simulation developed by our research group in recent years.The works of this thesis mainly include the following aspects:(1)Discuss how to obtain the four coupled equations of different polarization components and different frequencies components(belonging to different sidebands)of the probe pulse in a five-level Mtype EIT medium;(2)When the probe pulse has a long duration,the dispersionterms in the coupled equations can be ignored.Under this condition,Stokes parameters can be introduced and Poincar?e sphere representation can be used to analyze the evolution of different polarization components of the probe field;(3)In weak-light level,the conditions of polarization instability and polarization self-trapped states of the probe field are discussed,and the polarization rotor can be realized through a polarization instability;(4)For long probe pulses,four-wave mixing occurs between four components with different polarization directions and different frequencies of the probe pulse and exchanging energy with each other.For short probe pulses,the dispersion terms in the coupled equations must be preserved.Under this condition,the four-component weaklight ultraslow solitons can be generated in the system.The investigation of nonlinear polarization dynamics of weak light in coherent atomic media not only has certain significance for the development and improvement of the basic theory of weak light nonlinear optics,but also has potential applications in the development of weak light nonlinear optical devices,optical information processing and transmission,etc.