Research On Beam Clean Up Of Intracavity Raman Laser

Raman lasers have a wide range of applications in the atmosphere monitoring,laser radar,laser communications and other fields.Stimulated Raman scattering can change the original wavelength to obtain a new band of Raman scattering,which drives Raman laser becomes an important direction of development.Due to stimulated Raman scattering,Raman beam clean-up effect caused by non-phase-matching is an important characteristics for stimulated Raman scattering,which has a significant impact on operation of Raman laser.Laser rate Equations is an effective tool for analyzing the characteristics of Q-switched lasers,but most of the existing rate equations of intracavity Raman laser are based on the plane-wave approximation or single transverse mode approximation,which cannot explain the Raman beam clean-up phenomenon in theory.According to this problem,study of theory and experiments was established in this paper.In theory,based on multi-transverse mode operation,theoretical model of intracavity Raman laser rate equations were built for analyzing intracavity mode competition of intracavity Raman laser under beam cleanup effect,which was more reasonable than plane-wave approximation or single transverse mode approximation.Using two different rear mirror of curvature radius of 300 mm and 1000 mm,the diode-pumped Cr4+:YAG c-cut Nd:GdVO4 self-Raman laser is investigated experimentally.The influence on output power,pulse energy and pulse width by pumped power is discussed with the combination of theoretical simulation.A maximum 1176 nm output power of 815 mW is obtained at incident pump power of 6.73 W while the 300 mm rear mirror is employed in steady operation state,the corresponding conversion efficiency and slope efficiency from pumped source to Raman laser is 12.1% and 15%,respectively.A optimum 1176 nm output power of 976 mW is obtained at incident pump power of 9.4W while the 1000 mm rear mirror is employed,the corresponding conversion efficiency and slope efficiency from pumped source to Raman laser is 10.4% and 12.4%,respectively.Combining experiments and theoretical results,the impact on laser conversion efficiency by Raman beam cleanup phenomenon was expressed,which the ratio of pump light and intracavity beam exist an optimum and is not as small as possible.In our experimental study,keeping beam radius of intracavity and pump similar and making large mode size,high coupling efficiency of pump beam and intracavity laser is obtained and the generation of high order mode of intracavity fundamental light is suppressed,which is available for improving the conversion efficiency from fundamental light to Raman laser.