Research On Four Wave Mixing Effect In Double Electromagnetically Induced Transparency System

Four-wave mixing(FWM),as an important third-order nonlinear effect,has been widely studied since last century.When atomic coherence effect such as electromagnetic induced transparency(EIT)is applied to the study of FWM,whose efficiency will be significantly enhanced.Moreover,efficient FWM process is helpful for the generation of quantum correlated twin beams and then broaden its application in many fields such as quantum communication,spectral analysis and quantum imaging,etc..Based on the double EIT atomic system,the theoretical and experimental research related to FWM is carried out.The paper is mainly divided into the following four parts:Part 1: The physical concepts and background involved in this paper are briefly introduced.Part 2: The dual channel gain spectrum with double band is studied in double EIT system.In one of the EIT structure,the transparency window is manipulated to generate degenerate FWM by increasing the temperature of Cs vapor,and in the other EIT structure,the pump field is regarded as the dressed field for the degenerate FWM,resulting in the Autler-Townes(AT)splitting of the excited state.Because of quantum interference,the FWM signal is suppressed at the three-photon resonance,and the gain spectrum is changed from the single-frequency envelope to the "M" type double frequency bands.Moreover,the FWM gain signal is obviously enhanced because of the increased population in coherent ground state by the pumping of the dressed field.In theory,the method of double-sided Feynman diagram is used to carry out the theoretical analysis and simulation,which agree well with the experimental result.The AT splitting is explained by the dressed state,and its spacing versus the light power and frequency detuning of the dressed field is studied.Finally,the splitting of the double gain peaks is flexibly controlled by adjusting these parameters.Part 3: Multiple FWM processes in double EIT system are studied.For the double EIT atomic system as described in the second chapter,when adjusting the spatial structure of the two pump beams,it is found that multiple FWM processes will occur if the two EIT windows are completely overlap.The spatially separated four-partite light amplification can be observed experimentally.The four beams are classified into two pairs with 9.2 GHz frequency difference.According to the momentum conservation and energy conservation,the possible FWM process is analyzed and discussed.The gain variation of the four-partite beams is studied by changing the power and frequency detuning of two pump beams.Part 4: The topological charge of orbital angular momentum(OAM)beam is measured by interference method.In order to put the OAM beam carrying topological charge into the FWM experimental study,it is first necessary to identify the OAM.In this chapter,the interference of spherical wave,plane wave and OAM beam with OAM beam is theoretically analyzed respectively.The corresponding interference patterns with different topological charges are simulated and analyzed.The experimental results are consistent with the theoretical simulation.It is proved that an efficient method for identifying the topological charge is obtained.