Study On Optical Bistability Of Four - Level Atomic System Induced By Quantum Coherence

Recent years, the investigation about nonlinear optical (NOL) characteristic has been one of the frontier research topics in the international optics academia. NOL have been extensively investigated in laser physics and quantum optics. Due to the optical bistability (OB) and multi-stability (OM) having wide applications, they have attracted the attention of many researchers. Many scholars have studied the characteristics of nonlinearity revolved around the interaction between the optical field and the atomic system, and have reached many important results, such as enhance the Kerr nonlinear in nonlinear media, electromagnetically induced transparency(EIT), spontaneously generated coherence, optical bistability and so on. As a result of the in-depth studies by more and more researchers, the optical bistability has been found in different media and materials constantly and the exploration of two-level and three-level are going full-fledged.While in this paper, depending on the quantum interference, I intend to investigate OB of the four-level tripod configuration atomic system inside a unidirectional ring cavity. The main parts of this dissertation are as follows:1. We introduce the present situation and the background of studies about the optical bistability. This chapter mainly describes the conception, the physical mechanisms, the classical theories and the study trends of the optical bistability, and put forward the research question of this paper and the solutions.2. We recommend the theory basis and the spontaneously generated coherence (SGC) that involved in this paper, the three pictures which describes the interaction between the optical field and the atomic in quantum systems(that is Schrodinger picture, Heisenberg picture and Interaction picture), the semi-classical theory about the interaction between the optical field and the atomic system, two methods in handling the interaction between the optical field and the atomic(probability amplitude method and density matrix approach), the propagation rules of light in media, as well as the basic theory and the research history about the SGC. In V-type three-level atomic system, the basic principle of the SGC is studied, and the existence condition of the SGC is given:first, the energy interval between two adjacent levels has to be small enough, that is near mergers; second, the two directions of transition dipole moment must be non-orthogonal. And the density matrix of V-type,∧-type and trapezoid type three level atomic system are deduced in the existence of SGC.3. We discuss the SGC effect and observe the optical bistability in this four-level atomic system. This paper shows that, by adjusting the intensity of the SGC, the generating and disappearing of the optical bistability is under control and the threshold value of the optical bistability is influenced. In the existence of SGC, by adjusting the relative phase, the OB and OM can be translated to each other, and the other parameters are with certain impact to the OB.