Electromagnetically Induced Grating In Multi-level Atomic System Modulated By Phase

The atomic coherence effect induced by external laser fields has greatly attracted the interest of researchers due to many novel optical phenomena derived from it.Electromagnetically induced transparency(EIT)and electromagnetically induced grating(EIG)have become the hottest topics in the field of quantum optics due to their important potential application.Because of the low absorption and high dispersion in EIT systems,under the modulation of periodic standing-wave fields,the absorption and dispersion of the weak probe field will also changes periodically.Therefore,the atomic medium exhibits the properties of grating which can diffract the energy of the probe field into specific direction.We called it EIG.In applications,people need to flexibly adjust the characteristics of diffraction gratings according to the actual needs.However,the performance of traditional gratings is difficult to change after its fabrication.EIG is the key to solve this application problem.Based on the above advantages,EIG has potential applications in optical quantum fields such as routing,all optical switches and splitters.In order to solve the problems of EIG such as low diffraction efficiency in high order direction,difficulties of realization in experimental because of its complex structure,we propose two schemes of two-dimensional(2D)EIG with simple structures and high diffraction efficiency in this dissertation.Moreover,based on relevant theoretical knowledge and simulation patterns,we also analyze the proposed two models of EIG.The main contents of this dissertation are as follow:A brief introduction was given to three pictures that depict the changes in the system over time.Under the semiclassical theory,we introduce the derivation process of the interaction Hamiltonian of the system,two approximations used to simplify the theoretical calculation and how to use the density matrix to describe the interaction between light and substance.The generation conditions and principles of EIT and spontaneous generated coherence(SGC)are introduced in detail.The relative phase sensitivity effect in the closed-loop atomic system is also described.We proposed a theoretical scheme for 2D EIG in a closed-loop four-level atomic system driven by a weak probe field,a traveling-wave control field,two orthogonal standing-wave fields and a microwave field.Under the modulation of the laser field,we can obtain the low probe field absorption with large phase modulation.After the investigation,the results show that the diffraction pattern and efficiency of the EIG could be adjusted effectively by the probe field detuning,the incoherent pump field intensity,the interaction length.Based on closed-loop atomic system,the quantum interference can be manipulated by the relative phase,which can be used to regulate the diffraction pattern and efficiency of the 2D EIG.In addition,a new scheme for 2D EIG is proposed based on SGC in a closed-loop type(43)atomic system,in which the atom interacts with two orthogonal standing-wave fields and an incoherent pumping field,so the absorption and dispersion properties of atomic medium will also be modulated periodically.Due to periodical modulation,the gain of probe field accompanied with large dispersion can be obtained in atomic medium.The diffraction feature and efficiency of the gratings could be adjusted by the probe field detuning,the interaction length,the intensity of incoherent pump field,and the relative phase as well.This 2D grating scheme has only three energy levels and only three laser fields,which making it easier to realize than other schemes.Therefore,the scheme of 2D EIG we presented may has some potential application in beam splitting and all-optical switching.