锯齿形板条抽运结构的热效应数值比较

激光二极管抽运的全固态激光器中,除了激光介质的温度分布和热透镜效应以外,抽运、冷却结构对获得高光束质量、高功率激光输出至关重要。基于热传导方程,在相同的抽运功率和传导冷却边界条件下,对单侧面抽运锯齿形(zigzag)板条、单侧面键合锯齿形板条、部分抽运板条三种不同抽运结构的温度分布、热致应力、温度导致的折射率变化进行了详细的分析,并通过光线追迹方法,比较了光束在锯齿形面内和垂直于锯齿形面内的光程差,由光程差曲线分析了激光束的热透镜效应。对三种抽运结构的端面温度、端面变形和端面变形导致的光程差也进行了对比分析。结果表明,三种抽运结构在锯齿形面内的光束均表现为发散特性,在垂直于锯齿形面内的光束表现为热聚焦效应,温度导致的热聚焦特性相差不是很大。而在消除端面效应方面,键合激光板条具有明显优势。最后,提出了热透镜效应的补偿方法。     

掠入射板条放大器链的热效应模拟分析

对LD泵浦的掠入射板条放大器链系统激光介质的热效应进行研究。针对掠入射放大器结构建立了相应的热力学模型,对激光介质的温度场分布、热致波前畸变和热透镜效应进行了详细的理论分析。利用有限元分析软件COMSOL模拟了晶体内部的温度、应力及应变的分布情况,并进一步讨论了板条厚度、泵浦尺寸以及种子光入射角对光程差和热透镜造成的影响。结果表明,随着泵浦光斑尺寸和种子光入射角的增大,光程差变小,热透镜效应减弱;板条厚度对光程差和热透镜的影响较小。模拟计算结果对于预测板条热效应的强弱、热效应的补偿,以及放大器链结构参数的设计提供了依据。     

激光二极管抽运Nd:YVO4晶体的三维热效应分析

针对激光二极管抽运的以Nd:YVO4板条晶体为增益介质的激光器件,基于有限容积法数值分析各向异性介质的热传导方程,给出了Nd:YVO4晶体板条结构的热分布数值模型,并分别模拟仿真了808nm半导体激光器双端端面抽运,大面均匀抽运,大面周期分布抽运三种抽运结构,得到了Nd:YVO4板条晶体在这三种抽运结构下的非稳态时不同时刻的温度曲线和稳态时的三维温度分布切面图.     

梯度掺杂Yb ∶YAG重频激光器热管理研究

为了改善重频激光器的热性能,本文采用了键合Yb ∶YAG晶体薄片作为激光增益介质,介质中掺杂粒子浓度呈梯度分布.文章计算了不同参数条件下介质抽运过程,得到介质内部的储能,温度和应力分布,并从中选出较为优化的介质参数.计算表明,采用梯度掺杂的方法,介质温度降低,形变和热应力减小,波前畸变改善.理论上证明了采用梯度掺杂的方法改善热管理的可行性. 关键词： 梯度掺杂 键合 Yb ∶YAG 热管理     

波面热畸变自校正型板条增益介质的瞬态温度分布

提出一种新的激光增益介质板条抽运结构,这种结构能对由激光增益介质板条温度分布不均所造成的波面热畸变实现自校正,并建立了这种抽运结构下激光增益介质板条的瞬态温度分布理论模型,通过解热传导方程,推导出板条增益介质的瞬态温度分布的解析表达式。同时对抽运参量分别为抽运脉冲能量为5.8×104J、抽运重复频率为2Hz和抽运脉冲能量为3.2×104J、重复频率为10Hz两种情况下两种下N-31型钕玻璃板条的瞬态温度分布分别进行了数值计算,分别给出两种情况下10s内和60s时钕玻璃板条的温度分布图并对结果进行了分析和对比,表明采用这种抽运结构的增益介质板条激光器可以以类似热容激光器的方式在短时间内实现高平均功率、高光束质量运转。     

角抽运Yb:YAG激光器

报道了一种高功率准三能级激光器角抽运方法，抽运光从板条激光器结构中的板条工作介质的角注入，综合考虑抽运吸收、抽运亮度、晶体的掺杂浓度以及晶体尺寸等因素，进行了角抽运复合Yb:YAG激光器设计，实验上获得了最大连续输出功率400W, 斜效率28%的输出，实验结果充分证明了角抽运原理的正确性和应用于高功率激光器方面的可行性. 关键词： Yb:YAG 角抽运 复合晶体     

梯度掺杂Yb:YAG重频激光器热管理研究

为了改善重频激光器的热性能,本文采用了键合Yb:YAG晶体薄片作为激光增益介质,介质中掺杂粒子浓度呈梯度分布.文章计算了不同参数条件下介质抽运过程,得到介质内部的储能,温度和应力分布,并从中选出较为优化的介质参数.计算表明,采用梯度掺杂的方法,介质温度降低,形变和热应力减小,波前畸变改善.理论上证明了采用梯度掺杂的方法改善热管理的可行性.     

流体直接冷却薄板条介质温度及应力的解析表达

基于对流传热和热传导原理, 建立了流体直接冷却均匀抽运薄板条激光工作介质的热效应分析模型, 采用平面应力近似和最小功原理, 得到了板条工作介质内部温度分布和应力分布的解析表达式. 研究了不同流道厚度时对流热交换系数和冷却液温升与流体流速的关系, 分析了流道厚度对工作介质的温度分布和应力分布的影响规律, 讨论了之字形和直通光路时, 热致波前畸变随产热功率的变化趋势. 结果表明: 层流和湍流时, 较厚的流道可以实现更好的热管理效率; 增益介质中的热分布关于中心平面对称, 纵向最大温升出现在出水口端, 最大应力畸变集中在板条两端及其侧边; 流道厚度较大时, 工作介质更易形成一维的温度梯度, 产生的应力更小; 之字形光路可以明显缓解热光效应导致的波前畸变.     

脉冲激光二极管侧面抽运Nd:YAG激光器晶体时变热效应

采用数值计算的方法,对脉冲激光二极管三向侧面抽运固体激光器中,激光晶体的温度场时变分布进行了计算. 分析了三向侧面抽运情况下晶体内光强分布,在此基础上,采用有限元法,以脉冲激光二极管侧面抽运Nd:YAG激光器为例,对单脉冲过程中晶体温度分布及其影响因素进行分析. 结果表明,晶体升温过程受到抽运条件以及散热条件的影响,但是主要受到抽运条件即抽运光强度和光束半径的影响,降温过程受到晶体热物性参数和晶体半径以及散热条件的影响. 当晶体温度达到周期性分布后,由于晶体径向温度梯度的周期性变化,引起通过晶体的平面光波的中心和边缘光线相对光程差也随时间作周期性变化.     

脉冲激光二极管侧面抽运Nd∶YAG激光器晶体时变热效应

采用数值计算的方法,对脉冲激光二极管三向侧面抽运固体激光器中,激光晶体的温度场时变分布进行了计算. 分析了三向侧面抽运情况下晶体内光强分布,在此基础上,采用有限元法,以脉冲激光二极管侧面抽运Nd∶YAG激光器为例,对单脉冲过程中晶体温度分布及其影响因素进行分析. 结果表明,晶体升温过程受到抽运条件以及散热条件的影响,但是主要受到抽运条件即抽运光强度和光束半径的影响,降温过程受到晶体热物性参数和晶体半径以及散热条件的影响. 当晶体温度达到周期性分布后,由于晶体径向温度梯度的周期性变化,引起通过晶体的平面光波的中心和边缘光线相对光程差也随时间作周期性变化. 关键词： 激光二极管侧面抽运固体激光器 热效应 有限元法 时变过程     

Numerical modeling of the thermal lensing effect in a grazing-incidence laser

The numerical modeling of thermal lensing effect is investigated in a grazing-incidence laser. The deformation of the bounce face is introduced into the modeling for the first time, and the Gaussian distribution of the pump light and the anisotropic heat conduction are considered. The results indicate that the proportion of the deformation on the bounce face to the thermal lensing effect is as high as 80% for small grazing-incident angle of 5°. The thermal lensing effect sensitively depends on the pump power, grazing-incident angle and the pump distribution in a grazing-incidence bounce geometry laser.     

The thermal effect in a grazing-incidence slab laser with the novel composite cooling method

The thermal properties of the grazing-incidence slab laser are investigated when cooling with a novel composite method, both conducted cooling and air cooling. The 3D temperature distribution and the correspondent thermal lensing effect were analytically modeled and numerically calculated. The absorption saturation and stress-optic effect were taken into account in the modeling. The influence of the parameters of the laser on the thermal lensing effect were investigated in detail. The results show a lower temperature and weaker thermal lensing effect for the composite cooling than for the traditional contaction cooling.     

LDA侧面Zigzag泵浦多边形薄片激光放大器模拟与实验研究

介绍了一种激光二极管叠阵（LDA）侧面Zigzag泵浦多边形薄片激光放大器构型，采用三维光线追迹方法进行了详细的模拟仿真，优化设计了此放大器系统的泵浦耦合结构，主要研究了多边形增益介质的掺杂离子浓度与侧面切角对介质内部泵浦光分布的影响。在晶体厚度1.5 mm、端面口径16 mm的条件下，侧面切角在35°～65°，Nd3+掺杂浓度为0.20 at.%～0.30 at.%时，模拟仿真中Nd:YAG多边形薄片对泵浦光的吸收分布较均匀，泵浦光分布均匀性均优于0.1，同时在实验中得到了平顶的荧光分布和增益分布。介质内储能的均匀平顶分布有利于实现高功率高光束质量的激光输出，为侧面Zigzag泵浦多边形薄片激光器系统的设计与进一步实验提供了重要参考。     

Grazing-incidence YVO4-Nd:YVO4 composite thin slab laser with low thermo-optic aberrations

We present a novel grazing-incidence composite thin slab laser (CTSL) with an almost aberration-free gain medium. The laser consists of a 260-microm thin Nd:YVO4 plate that is diffusion bonded to an undoped YVO4 slab. The Nd:YVO4 plate is cooled at just one side, suppressing temperature gradients that would induce wave-front distortions in the laser field. The pump light of a noncollimated diode bar is directly coupled into the undoped YVO4 slab and guided by total internal reflection to the attached Nd:YVO4 plate. Since any pump-beam-shaping optics can be omitted, the laser is simple and compact. We obtained transverse multimode optical output powers of 14 and 9.3 W with M2 < or = 1.3.     

Analytical model of transient thermal effect on convectional cooled end-pumped laser rod

The transient analytical solutions of temperature distribution, stress, strain and optical path difference in convectional cooled end-pumped laser rod are derived. The results are compared with other works and good agreements are found. The effects of increasing the edge cooling and face cooling are studied. It is found that an increase in the edge cooling has significant effect on reducing the maximum temperature that can be reached in the laser rod but it has no effect on the value of optical path difference. It is also found that increasing this type of cooling significantly reduces the time required to reach the thermal equilibrium with a slight increase in the max. tensile hoop stress that can be reached as the cooling increases. On the other hand, increase in face cooling reduces the response time, optical path difference and the maximum temperature that can be reached in the laser rod but a significant increase in the max. tensile hoop stress is observed. A matching between the advantages of these two type of cooling may be useful for a designer.     

Thermal optics distortion of face pump slab lasers with two pump arrangements

Two pump arrangements, which are the slow axis and the fast axis of LD stacks parallel to the length direction of the slab, are simulated. From the results the optical intensity along the width of the slab is Gaussian and super-Gaussian distribution, respectively. Then based on heat conduction equation and conductively cooling boundary condition, the calculation of the distribution of absorbed pump power, temperature and thermal stress with the tool of finite element analyses is performed. From these results we numerically calculate the thermal focusing in zigzag and perpendicular zigzag planes using the ray tracing method running at low and high repetition rates. It is found that the temperature distribution along width has a significant impact on the thermal stress and thermal optics distortion, especially running at high repetition rate or high average power. Finally, the conclusion was that the pump arrangement with the fast axis of LD stacks parallel to the length direction of the slab is superior to the slow axis of LD stacks parallel to the length direction of the slab in decreasing thermal lens effect and obtaining high beam quality.     

数值模拟抽运分布对端泵激光器晶体热透镜球差的影响

为了研究端面抽运情况下,激光晶体在不同分布的抽运光抽运时热透镜球差的变化,通过对稳态热传导方程和Zernike多项式的求解,建立了热透镜球差与抽运光强度分布的模型,对模型进行了理论分析和仿真研究,并对仿真结果做了进一步理论和仿真分析.结果表明:在相同的抽运功率下,二阶超高斯分布抽运光抽运时球差最大,且随着抽运分布系数k的增大(除高斯分布外)球差逐渐减小;随着抽运功率的增加,抽运分布系数k对球差的影响逐渐加重,且不同分布系数k所产生的球差差距逐渐增大;并对二阶超高斯分布抽运光抽运得到最强激光功率的照射范围进行了理论分析和仿真分析,得知在相同抽运功率下,二阶超高斯分布抽运光得到最强激光功率的范围最宽为0.30—0.63倍高斯半径.