Investigations on Nonlinear Properties of Light in Cold-Atom Medium
|School||East China Jiaotong University|
|Course||Materials Physics and Chemistry|
|Keywords||quantum interference electromagnetically induced transparency ultraslow optic optical bistability and multistability|
Nonlinear effects of light are generally very weak under the nonresonant condition. The near-resonant condition is capable of enhancing nonlinear effect but increased absorption is taken place. Thus pepole used to consider that it was difficult to enhance nonlinearity without suffering serious absorption.Electromagnetically induced transparency solves this difficulty. It is possible to enhance nonlinearity effects under weak field conditions. The absorption against probe laser field can be largely suppressed via quantum interference by coupling laser fields. The wave propagation in an optical medium under EIT configuration displays many striking features such as signifcant group velocity and great change of dispersion effect, which offers a new control method to nonlinear effects. The same theory is used to control ultraslow optical propagation and optical bistability/multistability.In recent years there has been much interest in the light nonlinearity phenomenon on cold-atom medium, due to its potential applications in optical buffers, storage, swithes, memories, and transistor.In this paper, we mainly discussed nonlinear optical features and their applications by quantum theroy. The work of our paper can be divided into the following three parts.(1) We study the quantum interference effect on a ladder-four-system which interacts with three light fields. Our calculation show the various laws of the dispersion curve and the absorption curve via couple field changes. Under weak driving fields condition, the system appears to be hole burning in the dispersion curve and the absorption curve. With the increasing of them, two electromagnetic induced transparency windows are demonstrated. The position and width of windows can be controlled by driving fields intension and detuning. Finally, the explanation of these phenomenas are given by using the dress state threoy.(2) Without need of another control light, we analyse in a time-dependent way a new scheme to achieve ultraslow propagation of the input probe field through a medium composed of two-level atoms where their upper level is split into two hyperfine sub-levels via some applied static field such as a DC magnetic or a DC electric field or whatever other static field. Meanwhile we compared it with theΛ?type EIT scheme in details.(3) We analyze optical bistable behaviour in a V ?type three-level atomic system driven by a probe field by means of a unidirectional ring cavity. The probe field is applied to two transitions simultaneously. The interference between decay channels is important. We show that atomic coherence effect could significantly decrease the optical bistability threshold. The influence of the atomic cooperation parameter, the width between two upper levels and the detuning on atomic OB behavior is also discussed.Finelly, we study optical bistability and multistability behaviour in a ladder-type four-level atom in a undirectional ring cavity driven by three laser fields. Three paths of photon transition are coupled with three laser fields. In this case,The laser field coupleing with the middle transition is very important. When it is increased, optical bistability threshold could significantly decrease and optical multistability can be seen. The laser field coupleing with the middle transition is very important. The function of the laser field coupleing with the upper transition is also discussed. We analyse the effect of the detuning of probe field and atomic cooperation parameter.