Research On LD-pumped KGW Raman Laser Based On A Cascaded Coupling Cavity

All-solid-state Raman lasers are important components and research objects in the laser field.At present,diode-pumped solid-state lasers are no longer limited to a single scientific research,and have a wide range of applications in military,biology,laser medicine,communication technology and other fields.However,at present,the output power level of the solid-state Raman laser is low and the spectral purity is low,so it is particularly important to solve the problem of gain competition between multi-order Raman laser.The main purpose of this paper is to establish a theoretical model of a cascaded coupled cavity to control the gain competition between multi-order Stokes light,and on this basis the preliminary experimental research on active Q-switched pulsed Raman laser and theoretical optimization design of continuous wave Raman laser are carried out to explore the optimization scheme for realizing high-power pulsed and continuous wave solid-state Raman lasers.In this paper,the LD direct pumping method is adopted,with the Nd:YVO4and the KGd（WO₄）₂as the laser and Raman crystal,respectively.The specific work is as follows:Theoretical aspects:At first,the principle of stimulated Raman scattering is explained in theory,which is mainly used the nonlinear optical coupled wave equation;based on the general solid laser rate equation,the first-order Stokes Raman laser rate equation is used as an example to analyze the Raman solid laser rate equation.Secondly,the cascade effect in the process of high-order stimulated Raman scattering is introduced.A new cascade coupling cavity structure is proposed for the gain competition phenomenon,and the method of matrix optics is used to design the cascade coupled resonant cavity,The first-order,second-order,and third-order Stokes Raman rate equations in the cavity are established to analyze the variation law of particle number density in the three-stage cascade coupled cavity end-pumped by the LD.Then,the third-order Raman rate equations of active Q-switched pulsed and continuous wave KGW Raman solid-state lasers are solved by using MATLAB software,the dynamical process of the fundamental frequency light and each order Raman laser are analyzed and compared.The method of matrix optics is used to design the two different resonant cavity to obtain the most optimized resonant cavity.At the same time,the laser crystal and Raman crystal used in this article are introduced in detail,and the threshold formula of the solid Raman laser is analyzed to explore the factors that influence the threshold.Thereby reducing the thermal effect and increasing the Raman gain in the continuous Raman laser.Experimental aspects:a preliminary experimental study was carried out on the active Q-switched pulsed KGW Raman laser,and the optimal resonant cavity with the optimal cavity length and curvature of the input mirror and output mirror obtained in the optimal design of the resonant cavity was selected for experiments.By adjusting the pulse repetition frequency and the pumping current,the width of the 1177nm first-order Raman light pulse can be as narrow as 4.6ns.