Research On Optical Bistability Of Multi-level Atomic System Induced By Spontaneous Emission Coherence

Since the advent of lasers,nonlinear optics has been favored by researchers as a new discipline,and has been studied extensively and deeply with quantum optics and laser physics.The interaction between laser and matter has produced a series of interesting quantum coherence effects,such as:electromagnetic induction transparency,coherent population trapping,lasing without inversion.These quantum coherence effects have in turn promoted the development of nonlinear optics,such as quantum coherent induced kerr nonlinearity,optical solitons,optical bistability and so on.Optical bistability has potential application value in many aspects such as optical storage,all-optical switch,electro-optical conversion,optical transistor,logic circuit and so on,which has caused many researchers to carry out a large amount of research on it theoretically and experimentally.As is well known that building quantum coherence experimentally can effectively modulate some nonlinear processes to produce some phenomenons we are interested in.Spontaneous generated coherence(SGC)generated by incoherent spontaneous emission processes,has attracted a great deal of research interest.It refers to the coherent caused by different spontaneous emission channels and provides a constructive method for controlling the optical response in atomic media.Therefore,a large number of important effects based on SGC have been studied in atomic systems.Based on the spontaneous generated coherence effect,we mainly investigate the optical bistability and optical multistability effects in a the tripod-type four-level atomic system.The main thesis includes the following four parts:In the first part,we mainly introduce the research background and current situation of optical bistability,and then concretely describes the concept of optical bistability,the principle of generation,the related devices and classification,and the semi-classical theory of optical bistability.In the second part,we introduce the basic theoretical knowledge about the interaction between light and matter in nonlinear optics,and mainly includes the three basic physics picture in quantum mechanics:Schrodinger,Heisenberg and interaction picture,Hamiltonian of interaction between light and medium in dipole approximation and rotating wave approximation,Two methods of interaction between light and matter under semi-classical theory-probability amplitude method and the density matrix method,the propagation of light theory.In the third part,the basic conception of spontaneous generated coherence and its generating principle are briefly described firstly.Taking the V-type three-level atom as an example,we obtained the conditions satisfied by spontaneous generated coherence,and deduced the density matrix equation of the V-type,lambda type and ladder three-level atoms when exist spontaneous generated coherence.Based on this,we study the optical bistability and optical multistability properties of the tripod-type four-level atomic system under the multiple spontaneous generated coherence.Studies have shown that optical bistability is sensitive to the spontaneous generated coherence effects via changing the strength of multiple spontaneous generated coherence.We also compared the effects of single,dual,and triple spontaneous generated coherences on optical bistability.The results show that multiple spontaneous generated coherence can enhance or reduce the threshold of optical bistability.In addition,in this atomic system,we also study the effect of multiple relative phases on optical bistability and optical multistability.Due to the formation of a closed annular structure between the light field and the atomic level,the coherence of the system can be effectively regulated by adjusting the relative phases between the various application fields.Therefore,we can regulate the appearance and threshold of optical bistability by adjusting the relative phase.Further study found that optical multistability can also be achieved by adjusting the relative phase,and the switching optical bistability to optical multistability can be realized under the appropriate parameters or vice versa.In the fourth part,we summarize the main contents of this thesis and look forward to the prospect of application of optical bistability in the future science and practical life.