Experimental Research On Optical Amplification Based On Stimulated Degenerate Four-wave Mixing

The optical amplification effect based on the interaction between light and atoms is one of the important representations of atomic nonlinear effects.It has important research value in the preparation of entangled correlated optical fields,optical nonreciprocal transmission and all-optical-controlled quantum devices,and so on.Since the end of the last century,people have conducted a lot of research on optical nonlinear effects based on atomic coherence,and discovered many classical and interesting physical phenomena,such as coherent population trapping(CPT),electromagnetically induced transparency(EIT),electromagnetically induced absorption(EIA),four-wave mixing effect(FWM),etc..And FWM based on atomic coherence has become an important research direction of current quantum information processing.One of the more well-known research contents is that in the double?-type three-level alkali metal atom system,the large frequency difference quantum correlation light field can be generated through the stimulated FWM process.Because of its high gain and high entanglement characteristics within a wide frequency range,it has been paid attention and widely used.For example,high-sensitivity spectral detection,long-distance quantum communication and quantum imaging,etc..These research have further enriched the physical connotation of FWM.In this paper,the optical amplification effect based on degenerate two-level system is experimentally studied in the hot Cs atoms.The research content is mainly divided into the following four parts:Part 1:The scientific background and application of optical amplification effect with related methods of generating optical amplification are briefly introduced.Part 2:Based on the D1 line of Cs atom,the optical amplification effect induced by degenerate FWM is experimentally studied using a 25mm long Cs atom cell.The results confirm that only when the angular momentum of the ground state is greater than or equal to the angular momentum of the excited state(F_g?F_e),the EIT effect can be transformed into the nonlinear FWM effect,and the more efficient DFWM signal can be obtained when the angular momentum of the ground state is equal to the angular momentum of the excited state(F_g=F_e).Part 3:According to the experimental results,a qualitative analysis is given considering all the Zeeman sublevels of the two-level system.The analysis shows that the stable?-type coherent dark-state chain formed by ground state Zeeman sublevels is a necessary condition for the generation of FWM.Furthermore,the N-type cyclic transition path which leads to the effective atomic population transformation induces the optical amplification.By constructing an N-type transition energy level,we theoretically simulate the optical amplification process,that is,with the Rabi frequency of the pump light increased,the transmission of the signal changes from the transparency effect to the optical amplification.Part 4:For theF_g?F_e transition,the influences of experimental parameters on the amplified efficiency of DFWM are studied,such as pump power,atomic number density and pump frequency detuning.Furthermore,the experimental results show that the amplification efficiency of DFWM can be significantly improved by introducing an additional 852nm pumping light.By selecting the appropriate pumping energy level and without changing the length of the Cs cell,the gain with 10 times can be obtained.As an example of the transitionF_g=4?F_e=4,it shows that changing the length of the Cs cell is also a way to improve the amplification efficiency.