Theoretical Study Of Optical Nonlinearity Based On The Interaction Of Vortex Light And Atoms

Vortex light beams with helical wavefronts spiraling along the beam direction have attracted much attention in recent years due to their photons carrying orbital angular momentum.Vortex light has been used in many frontiers such as quantum communication,quantum information storage,high precision measurements and manipulation of the microscopic particles.In quantum optics,the interaction between vortex light and atoms has become a hot research topic very recently.In this thesis,based on the interaction between(?)-type three-level atoms and two vortex light beams,we present a scheme to create a two-photon nonlinear process and explore the Kerr nonlinearity in electromagnetically induced transparency(EIT),the following two major results have been obtained:Firstly,under the condition of the two-photon resonance but large detuning for the single-photon transition,we have derived the effective two-photon Hamiltonian for the effective transition between the two lower atomic states by using James'effective Hamiltonian approximation method.A two-photon nonlinear process for the subtraction of the topological charges of the two vortex light fields has been realized in the case of weak light fields.Numerical simulation shows that the fidelity of the effective Hamiltonian and the original Hamiltonian can reach more than 99.95%.In addition,the effective two-photon coupling vortex field as a function of the spatial coordinate z has been studied by solving the Maxwell-Bloch equation.Secondly,based on the Kerr nonlinear theory in EIT,we investigate the absorption spectra and Kerr nonlinearity for a system of(?)-type three-level atomic medium interacting with two vortex light beams and examine their spatial dependence induced by the vortex light beams.Our numerical results indicate that the absorption spectra of the probe vortex field depends on the spatial distribution of the vortex light field,the number of absorption peaks depends on the topological charge of the probe vortex light beam,and the detuning for the probe field and the corresponding atomic transition?_p also has a certain influence on the absorption spectra;The spatial dependence of the refractive index of atomic medium mainly depends on the spatial distribution of the intensity of the control vortex light field.The detuning?_p also has a great influence on the nonlinear part of refractive index.