Coherent Manipulation Of Electromagnetically Induced Transparency Spectrum In Atomic Systems

Electromagnetically Induced Transparency(EIT)is a new phenomena of quantum optics, in which the probe field can't be absorbed by the atomic system under the action of another strong field. EIT has been observed in atoms, rare-earth doped crystal and semiconductor quantum well. EIT has many useful applications, such as lasing without inversion, the nonlinear optics at low light levels and subluminal or superluminal group velocity.The single EIT with only one transparency window in a three-level atomic system has been studied thoroughly. Recently, the single EIT has been generalized to the double or multiple EIT phenomena. In this thesis, we mainly discuss multiple electromagnetically induced one-photon transparency and double electromagnetically induced two-photon transparency in a five-level inverted-tripod scheme atomic system, and the multi-dark resonances induced by the coherent perturbations as well as the effects of the linewidth of the coupling field on the multi-dark resonances.The thesis is organized as follows: In the first three chapters we mainly introduce the development of EIT as well as its basic principle which includes the semiclassical theory describing the interaction between the field and atomic system.In 4 Chapter, we put forward a new five-level inverted-tripod scheme atomic mode, and investigate its multiple electromagnetically induced one-photon transparency and double electromagnetically induced two-photon transparency. We find that by adjusting the Rabi frequencies of the coherent fields, there appear triple, double and single EIT. In the triple EIT, the location of transparency windows can be controlled by adjusting the detunings of the coherent fields, and changes continuously, i.e. the probe field can propagate in an atomic medium without absorption in a certain range of frequency. This is useful in investigating the optical features of atomic system as well as multi-channel optical information transfer. We also investigate the effects of the Rabi frequencies and the detunings of the control fields on the two-photon absorption spectra. This is useful to realize two-photon entanglement, multi-channel optical information transfer, quantum information and the atomic optical property.In 5 Chapter, we use several weak coherent fields (coherent perturbations)to couple the ground level of coupling transitions in aΛ-type atom with the sublevels of a lower state, there appear multiply sharp and high contrast absorption lines in the probe absorption spectra. These absorption lines can be turned into gains under the pumping of a very weak incoherent field. Besides the absorption properties associated with the multi-dark resonances, we also investigate the dispersion properties. At the sharp absorption, the dispersion becomes very steep and its gradient slope is negative. When the incoherent field is pumping the atoms, the steep dispersion curve at probe gains becomes positive, i.e. the slow group velocity under gain without inversion can be realized. We also consider the effect of the linewidth of the coupling field on these optical properties. The linewidth mainly deduces the sharp absorption and the maximal dispersion, but does not influence the group velocity of the probe field. This property is very useful in manipulating the atomic optical responses.