热效应作用下高功率薄片涡旋激光器的模场结构  

Modal structure of high power thin-disk vortex laser under thermal effect

作　　者：连天虹[1] 窦逸群 周磊[1] 刘芸[1] 寇科 焦明星[1] Lian Tian-Hong;Dou Yi-Qun;Zhou Lei;Liu Yun;Kou Ke;Jiao Ming-Xing(School of Mechanical and Precision Instrument Engineering,Xi’an University of Technology,Xi’an 710048,China)

机构地区：[1]西安理工大学机械与精密仪器工程学院,西安710048

出　　处：《物理学报》2024年第16期89-101,共13页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:61805196,51875455)资助的课题.

摘　　要：激光介质热效应引起的谐振腔模场结构变化成为高功率涡旋激光器的一个关键问题.本文建立了环形光泵浦薄片激光晶体的温度场及热形变计算模型,将热效应像差作为谐振腔衍射积分方程的微扰,研究热效应对激光器模场结构的影响规律.具体研究了Nd:YAG,Nd:YLF和Nd:YVO_(4)薄片涡旋激光器的模场结构随泵浦功率、晶体吸收系数、晶体厚度的变化规律.研究结果表明,热效应使涡旋激光器模谱产生径向展宽,模式纯净度下降.泵浦功率越大,高阶径向模式占比越大,模场结构越复杂.泵浦功率升高时,Nd:YVO_(4)激光器的模谱展宽最大,Nd:YAG激光器的模谱展宽最小.晶体吸收系数越大,模谱展宽越严重;激光晶体厚度减小时,模谱展宽呈增宽趋势.Optical vortex beam has wide applications in areas of optical communication,lidar detection and optical trapping.To increase the operating distance,a high-power vortex laser source is necessary in these applications.However,the purity of the output vortex beam decreases with the pump power increasing due to the thermal effect of the laser medium.Therefore,modal field degeneration induced by thermal effect of laser medium has become a key problem in high-power vortex solid-state laser.To investigate this modal field degeneration,the heat transfer and thermal deformation model of an annular beam end pumped thin-disk vortex laser(Fig.(a))is established.The phase difference of the thermal effect is calculated based on this model.Then,the quadratic term is separated from the phase difference.The non-quadratic term,as a small perturbation,is substituted into the diffraction integral equation of the laser cavity.The modal field structure is obtained by using the perturbation method.The variations of the modal structure with pump power,absorption coefficient and crystal thickness are investigated for three kinds of laser crystals,i.e.Nd:YAG,Nd:YLF and Nd:YVO_(4).The results show that the modal field under thermal effect presents obvious deviation from the ideal mode at high power,and the modal structure shows that it contains many higher-order radial modes,with the angular mode order unchanged.Hence,the radial modal spectrum is broadened by the thermal effect.For an ideal vortex laser without thermal effect operating on the radial mode order 0 and angular mode order 1,Fig.(b)shows the modal structures with thermal effect under different pump power values with a laser crystal thickness of 1 mm.The ratio of the higher-order modes increases and the modal structure becomes more and more complex with the pump power increasing.The ratios of the ideal mode are 0.99,0.97,0.90,0.79 and 0.61,under the pump power of 10 W,20 W,40 W,60 W and 100 W,respectively.Moreover,the Nd:YVO_(4) laser has the largest and the Nd:YAG laser has the

关 键 词：固体激光器 涡旋光 热效应 径向模谱展宽 

分 类 号：TN248[电子电信—物理电子学]