The Investigation Of Semi-classical Theory For Optical Bistability And Multistability In Cold Atomic Medium

Optical bistability (OB) and multistability (OM) is an important research topic in the quantum optics and nonlinear optics, which has been widely studied both experimentally and theoretically due to its potential application, such as optical transistors, optical memory and optical switches and so on. Particularly, since the electromagnetically induced transparency in the cold atomic medium was discovered, phenomenon related to OB and OM in cold atomic medium have been studied more widely in semi-classical theory. The main content of this paper is to theoretically study OB and OM in four-level atomic medium using semi-classical theory. Specifically, the main work of our paper consists of the following sections:(1) Semi-classical theory for the interaction of two laser beam with three-level cold atomic medium is introduced.(2) OB behaviour in a typical four-level cold atomic medium is studied and OB characteristic of coherence probe field in the present of an additional coherence term, spontaneously generated coherence (SGC) term is analyzed. The influence of the intensity of the controlling field, SGC and the relative phase of the two applied field on the OB behaviour are also studied.(3) OB and OM characteristics of probe field in a four-level atomic medium with closed-loop configuration are studied. A new academic scheme for realizing the transition between OB and OM is presented. At the same time, the condition of realizing OM is investigated.(4) A simple academic scheme for realizing OM of probe field in a N-type cold atomic medium is presented and the influence of the intensity and frequency detuning of the controlling field on OB and OM characteristics are studied.