Study On Solid-state Actively Q-switched Intra-cavity Raman Laser

With the development of laser technology,the applications of laser are increasingly,such as lidar,laser communication,laser display.But,the existing range of laser spectrum cannot reach the requirements of different applications.So,it is very important to broaden the laser spectrum range.Stimulated Raman scattering is an important nonlinear optical frequency conversion method.It can not only fill up the spectral region that has not been realized by the traditional laser,but also has the effect of beam clean-up.Compared with other nonlinear optical frequency conversion methods,stimulated Raman scattering doesn't need phase matching,and the output beam has narrow spectral lines,high beam quality.Compared with external cavity Raman laser,the intra-cavity Raman laser has the advantage of compact structure,low Raman threshold,convenient for application.Besides,ways to obtain high conversion efficiency,high pulse energy and narrow pulse width of stokes laser output have been a hot spot in the field of Raman lasers.For intra-cavity Raman laser,fundamental photons,first order stokes photons,second order stokes photons exist in laser cavity simultaneously,the conversion processing is complicated.Moreover,the balance mechanism among the intensity of stimulated emission,first order stimulated Raman scattering,second order stimulated Raman scattering is not clear yet.Thus the optimization of cavity parameter is difficult.In this paper,theoretical and experimental studies on actively Q-switched intra-cavity Raman laser was made.The balance mechanism among stimulated emission and Raman scattering was explained for the first time,as far as we know.Based on that,cavity parameters for high pulse energy stokes output were optimized.The characteristics of laser output were consistent with the theoretical results experimentally.Specific work and results are as follows.1: Theoretically,the rate equations models of intra-cavity Q-switched first and second order Raman laser were established.Then the rate equations were solved by Matlab and 2nd stokes output characteristics were simulated through adjusting beam radius,cavity length and transmission of insert coupler.The balance mechanism among stimulated emission,first order Raman scattering and second order Raman scattering was explained for the first time,as far as we know.Based on that,cavity parameters for high pulse energy stokes output were optimized.2: Experimentally,in order to verify the optimization scheme of Raman laser cavity parameters for improving the output pulse energy,basic researches about Nd:YVO4 AO Q-switched laser and AO Q-switched Nd:YVO4 self-Raman laser were carried out,firstly.Then the study about Nd:YVO4 AO Q-switched coupled cavity Raman laser was studied.Furthermore,we insert another mirror to form the Raman cavity in the fundamental laser cavity.The ‘coupled cavity' for fundamental laser was formed when the high transmission of insert mirror was changed to be partially transmitting at fundamental laser wavelength.The coupled cavity can redistribute the fundamental photons density.Pure YVO4 crystal was used as Raman media.At last,a 2.7ns,67.8?J,1176 nm laser output was obtained,the characteristics of laser output were consistent with the theoretical results.