Research Of Absorption Properties Of Multi-level Atomic Systems By Using Optical Means

The optical field which resonantly drives the atomic system will be absorbed. In 1990s, the phenomenon that the field won't be absorbed by the atomic system under the action of another strong field has been found. Such phenomenon is called electromagnetically induced transparency (EIT). Based on the EIT, many interesting applications have been discovered. For example, the gain without inversion can be realized, which overcomes the energy dissipation of the traditional gain with inversion; Due to the fact that the atomic dispersion drastically varies with the field frequency, the group velocity of the field can be slowed down or even stopped. This can be useful in the storage of quantum information. Additionally, the giant nonlinear optics at low light levels can be realized by using EIT, which play an important role in all optical switching or other fields, and so on.While people are exploring the application of EIT, the model has been generalized from three-level to four-level atomic system. In the present thesis, we investigate the absorption properties of multi-level atomic system which is under the action of the coherent field or vacuum field from background. Not only single or multi-EIT appears, but also there is gain without inversion. This is useful in the essential features of atomic system, multi-channel optical information transfer and the generation of laser.The thesis is organized as follows: In Chap.1, the physical phenomena based on the atomic coherence have been introduced, and the development of EIT as well as its application is reviewed. In Chap.2 two-level atomic system is used to display the semi-classical theory describing the interaction between the field and atomic system. In Chap.3, the energy structure, Hamiltonian and equation of motion of density operator of three kinds of three-level atomic system inΛ,V andΞ-scheme are introduced, respectively. In Chap. 4, we study the probe absorption properties in a V -type three-level atomic system driven by a coherent field. In Chap.5, the effects of multiple vacuum-induced coherence on absorption properties in a four-level inverted-tripod scheme atomic system are displayed.The new results of this thesis are as follows,1. we investigate the probe absorption properties in a V -type three-level atomic system driven by a coherent field, and find that the present scheme not only can overcome the disadvantage of traditional laser gain, but also can be realized easily in experiment.2. The effects of multiple vacuum-induced coherence on absorption properties in a four-level inverted-tripod scheme atomic system are presented. The different vacuum induced coherence will affect the transparency spectrum in different ways. At the same time, the gain without inversion at different frequencies can be obtained.