The Influence Of Intracavity Fundamental And Raman Beam Overlapping On The Conversion Efficiency In The Coupled Cavity Raman Laser

Coupled cavity Raman laser's fundamental cavity and Raman cavity are nested and relatively independent.The Raman cavity is shortened compared to an intracavity Raman laser,so high Raman gain can be obtained through Raman crystal many times at the same time.And it can compress Raman laser pulse.The theoretical researches of Raman laser are based on the derivation of radiative transfer equation and rate equations.The existing theoretical model of Raman laser based on the single mode Gauss beam approximation can well describe the operation of the LD end pumped laser near the single mode operation.But the mode of laser between LD side pumped system and LD end pumped system is different.The fundamental laser of the side pump is usually multimode operation,and the Raman laser is basically single mode operation because of the Raman beam clean up effect.In order to solve this problem,this paper establishes the LD side pumped Raman laser theory model.In this theoretical model,we consider that the fundamental laser operates in TEM₀₀,TEM_01*and TEM₁₀0 and assume that pump laser is Top-Hat distribution.We give the normalized rate equations,then we model and program for the normalized rate equations.We simulate the operation of the laser in different normalized Raman gain M and normalized inverted population N.In experiment,we achieve the LD side pumped Nd:YAG module YVO₄ intracavity actively Q-switched Raman laser.A maximum output power of as high as 6.98W is obtained under a pump power of 117.7W and at a pulse repetition frequency rate of 15kHz,corresponding to an optical-to-optical conversion efficiency of 5.93%.We achieve the LD side pumped Nd:YAG module YVO₄ coupled cavity actively Q-switched Raman laser.We study the influence of the change of the curvature radius of the coupling mirror on the conversion efficiency,the curvature radius of the coupling mirror is 150mm,300mm,1000mm and 3000mm,respectively.It is found that the larger the curvature radius of the coupling mirror is,the higher the threshold is,the larger the conversion efficiency is.And we give the pulse waveform of fundamental laser and Raman laser at the maximum average output power of Raman laser.It is in agreement with the theoretical model.