Preparation Of Blue Light By Multi-Photon Excitation Based On Four Wave Mixing Process

Four-wave mixing（FWM）is a pump laser with two different colors of pumps,which are transmitted into the steam room composed of alkaline metal atoms to generate a new wavelength light process.The region of the spectrum from infrared to ultraviolet and deep ultraviolet can be covered by the newly generated light from these nonlinear processes。It has important application potential in quantum information processing,high sensitivity atomic imaging,submarine communication,optical data storage and so on.In this thesis,Coherent Blue Light（CBL）is studied in a heated Cesium（Cs）chamber based on the up-conversion process on FWM.Relevant research content can be divided into the following three parts:1)The background and significance of preparation of CBL from alkali metal vapor are studied.The research progress of preparation of CBL by different groups at home and abroad is introduced.The absorption and dispersion characteristics of FWM are analyzed,and the theory of phase matching in FWM is presented.2)Cs atoms are driven to the 6D_5/2 excited state by dual-color pump light at 852 nm and 917 nm in a heated Cs atomic steam chamber,and a higher power of 456 nm CBL is achieved under phase matching conditions.The dependence of the power and fluorescence of CBL on the experimental parameters（cesium vapor pool temperature,pump laser power and frequency detuning）is observed.Under optimal Cs steam cell temperature and pump laser power,the resulting 456 nm CBL power will be saturated.Meanwhile,in the co-propagating light field,the two-pumped laser causes Autler-Townes（AT）splitting,and large separation（193 MHz）is observed in the two-state structure.3)The preparation techniques of Vortex beam are introduced,and the advantages and disadvantages of these techniques are analyzed.At the same time,the detection methods of Topological Charge（TC）and the application of these detection techniques by different groups are described.Then,the generation of dual wavelength vortex blue light based on FWM is studied in heated Cs steam.In the experiment,the Gaussian Beam（GB）at 852 nm and 921 nm is transformed into Laguerre Gaussian Beam（LGB）by a Space Light Modulator（SLM）.The Cs atom is pumped to the highly excited state by the 6S_1/2→6D_3/2two-photon transition.Vortex Blue Light（VBL）with dual wavelengths 456 nm and 459 nm is observed in two downward transition channels:6D_3/2→7P_3/2→6S_1/2 and6D_3/2→7P_1/2→6S_1/2.The production of two kinds of blue light and the detection of TC are studied.The variation of the corresponding VBL is demonstrated by changing the Orbital Angular Momentum（OAM）carried by the 852 nm and 921 nm vortex lasers.Finally,it is observed that the OAM carried by the newly generated VBL satisfies the conservation law.