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The Study On Electromagnetically Induced Transparency (EIT) And Its Nonlinear Behaviors

Posted on:2008-06-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:L J YangFull Text:PDF
GTID:1100360302973390Subject:Optical Engineering
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This thesis studies theoretically the nonlinear behavior of an Electromagnetically Induced Transparency in the A-type configuration level systems in the presence of a driven field perturbing the hyperfine level coherence. The simplest EIT system is that of a three level atom interacting with a couple and a probe laser field, forming a so-called three level double resonance configuration. One of the interesting properties of the EIT is its narrow spectral width, especially, when two ground state hyperfine levels are coupled to a common excited level in a A-type configuration. In such a configuration, the width of an EIT resonance is mainly governed by the ground state coherence relaxation rates which can be of a few order of magnitude smaller than that of the optical transition. In this thesis, we present a theoretically study of spectral features of EIT resonance in the A-type configuration three or four level system, particularly, the nonlinear behavior of an EIT in the presence of a driven field perturbing the hyperfine level coherenceFirstly, the characteristics of an EIT resonance including the width and contrast is studied theoretically for an ideal three-level system in a A-type configuration. The optical Bloch equations are solved and the power broadening behavior of the EIT resonance is studied as a function of both couple and probe laser intensities over a broad range. In addition, the analytical expression of linewidth and contrast of EIT are derived under condition of the weak probe field. It is shown that the linewidth of EIT is governed by the coherent relaxation rate between two lower levels.Secondly, we study the nonlinear behaviors of an EIT resonance subject to a coherent field driving a hyperfine transition within the ground state in both a quasiA-type configuration four level systems and a closed three level system. In the quasi-Atype configuration four level systems we contrast two different situations. In one case the microwave driven transition shares a common level with the probed transition and in the second case it shares a common level with the coupled transition. In both cases the EIT resonance is split into a doublet and the characteristics of the EIT doublet are determined by the strength and frequency of the microwave driving field. The doublet splitting originates from the microwave field induced dynamic Stark effect. The situation changes when the microwave field is strong and the two cases are very different. One is analogous to twoA-three-level systems with an EIT resonance associated with each. The other corresponds to a doubly driven three-level system with microwave field-induced electromagnetically induced absorption resonance. The two situations are modeled using numerical solutions of the relevant equation of motion of density matrix. In addition a physical account of their behaviors is given in terms of a dressed state picture. In the closed three level system Multi-EIT windows are observed, and the dependence of frequency positions, separation between EIT windows on the intensity and frequency of driven field are obtained. It is shown that Multi-EIT windows is due to the dynamic "Stark" splitting of the level and are explained in terms of dressed states of the driven system.Finally in chapter 7 we discuss the narrow spectral lines in a (?)-type configuration three level and a quasi-(?)-type configuration four level system. The density matrix equations of motion in the dressed-state picture are derived, and the analytical expression of the linewidth of narrow lines as a function of parameters of the fields and level systems are obtained. It is shown that the linewidth of narrow lines is governed by the coherent relaxation rates between hyperfine levels. Consequently the essence of the narrow of the absorption spectral lines is the atomic coherence or quantum interference induced in a multi-level system.
Keywords/Search Tags:Quantum interference, Electromagnetically Induced Transparency (EIT), theΛ-type configuration level system, Dressed-state
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