Research On Design Of Resonator Structure Of LD-End-Pumped Solid-State Raman Laser

All-solid-state Raman laser has been widely used in various fields such as national defense,military,industrial processing,biomedicine.The resonator structure of all-solid-state Raman laser directly affects its performance,hence selection of resonator structure parameters is of great importance to improve the performance of Raman laser.In this paper,the design of resonator structure of LD-end-pumped all-solid-state Raman laser is investigated theoretically.Basis on the ABCD transfer matrix method,the size and distribution of TEM00 mode in the fundamental laser resonator with different structures are simulated and calculated using a Matlab program.Thermal lens effect in the crystal,and how resonator parameters,including the curvature radii of cavity mirrors and cavity length,affect cavity stability and mode sizes are systematically studied.The selection criteria of specific cavity structure and parameters in previous studies are summarized and verified by some preliminary experiments.These research results provide insights into the design and optimization of resonator structure of allsolid-state Raman laser.The specific research content of this paper is structured as follows:Firstly,the ABCD transfer matrix theory for the calculation of cavity mode parameters in laser resonator is investigated to master the basic principle of resonator design.Then we apply the theory to two specific Raman laser resonator structures,i.e.linear cavity and folded cavity.This provides a theoretical basis for the subsequent design of all-solid-state Raman laser resonator structure.Secondly,for linear cavity and folded cavity resonator structures commonly used in Raman lasers,the size and distribution of TEM00 mode in the fundamental laser resonator is calculated and analyzed.The thermal lens effect in the crystal,and how different curvature radii of cavity mirror and cavity length affects on resonator stability and mode sizes are investigated in detail.Then their effects on the output performance of Raman laser are analyzed.The results indicate that thermal effect on resonator stability can be significantly reduced by using large pump spot in the all-solid-state Raman laser.When linear cavity is adopted,usage of an output mirror with small curvature radius can reduce the spot size of fundamental laser inside the Raman crystal and improve Raman conversion efficiency.Yet simultaneously spot size inside the laser crystal will also be reduced.Hence a good mode matching between the oscillating laser and the large pump spot cannot be achieved by adjusting cavity length.In contrast,due to the focusing effect of folding mirror,there are two laser beam waists inside the folded cavity,and Raman crystal can be placed near the second beam waist.By using folding mirror and output mirror with small curvature radius,the spot size of fundamental laser inside Raman crystal can be reduced,and Raman conversion efficiency improved.At the same time,the spot size of fundamental laser inside laser crystal can be adjusted by changing cavity length to achieve a better mode matching with the large pump spot.Therefore,the design and optimization of folded cavity is more flexible than that of linear cavity.Thirdly,for orthogonally polarized dual-wavelength Raman laser,how curvature radii of mirrors and cavity length affect its output performance is systematically studied.The results indicate that,the larger curvature radius of the output mirror,the larger size of laser cavity mode in the laser crystal,and the better mode matching with the large pump spot.However,as fundamental laser cavity and Raman cavity share the same output mirror,Raman laser mode size in the cavity also increases,which leads to deterioration of mode matching between the Raman laser and the fundamental laser.Therefore,when selecting curvature radius of output mirror,the above-mentioned factors should be taken into account.Finally,it is found that,as curvature radius of the input mirror increases,mode matching between the oscillating fundamental laser,pump beam and Raman laser deteriorates.Hence,under the condition of ensuring cavity stability,the smaller the curvature radius of the input mirror,the better.