LD端面泵浦变热导率圆片Yb∶YAG激光器的热效应

针对激光二极管端面泵浦圆片Yb∶YAG晶体产生的热效应问题,以实际工作特点为基础,通过热传导理论分析了热效应。分析了不同泵浦功率、超高斯阶次、光斑半径、晶体尺寸因素对变热导率圆片Yb∶YAG晶体温度场的影响。研究结果表明,使用泵浦功率为60W、超高斯阶次为5、光斑半径为400μm的泵浦光对含质量分数为8%、晶体半径为4mm、厚度为0.5mm的圆片Yb∶YAG晶体进行泵浦,在将晶体的热导率分别视为常量和变量时,泵浦端面获得的最大温升分别为52.15℃和59.51℃。根据计算结果,设计了适合的激光器热稳腔,能充分抑制激光器产生的热效应问题。     

Yb:YAG薄片激光器多通泵浦耦合系统设计与实验

 介绍了基于Yb:YAG薄片的16通泵浦耦合系统的设计方法,建立了泵浦系统的模型,对模型进行了模拟。以16通泵浦耦合系统为基础,通过微通道冷却,利用国产单片直径10 mm、厚度为250 μm、掺杂原子分数为10% 的Yb:YAG薄片进行了实验研究。在泵浦功率为69.5 W时,采用曲率半径为－800 mm的输出镜,获得了27 W的1 030 nm连续激光输出,光光转换效率为38.8%;采用曲率半径为－2 000 mm的输出镜,获得了18.65 W的1 030 nm连续激光输出,光束质量平分因子小于等于1.1,光光转换效率为26.8%。     

LD泵浦固体激光器基模振荡光的场分布噪音

通过调整泵浦光直径,使得LD端面泵浦固体激光器的振荡光工作于基模.在排除高阶横模的条件下,测量了由于热透镜的不稳定引起的光场场分布的噪音.实验发现,基模振荡光的高斯半径、光束指向角都在波动,而且光斑存在畸变波动.对一个未采取抑制措施的2W连续LD端面泵浦Nd:YAG固体激光器进行了测量.结果表明,在总功率不变的情况下,激光束峰值点附近的光强波动达到6.3%;激光的高斯半径波动达到5.8%;激光的指向角波动达到0.3mrad.     

新型全固态激光器作用过程中的激光参数分析

对影响LD泵浦的Nd∶GdVO4,Nd∶YVO4和Nd∶YAG激光器输出特性的增益介质长度、腔内损耗、输出镜透过率、泵浦光和振荡光的光斑大小进行了分析和数值模拟。当腔内固有损耗为2%,输出镜透过率为10%时,Nd∶Gd-VO4,Nd∶YVO4和Nd∶YAG晶体的振荡阈值分别为1.77W、0.55W和3.34W。在25W泵浦功率下,利用1mm长的Nd∶GdVO4,Nd∶YVO4和Nd∶YAG晶体可分别得到13.17W,13.26W和8.43W的输出功率,相应的输出镜最佳透过率分别为24%,44%和16%。     

LD单端泵浦变热导率Nd∶YAG方形热容激光器温度场

对方形激光晶体的实际工作特点进行分析,根据热容激光器的管理模式,建立泵浦阶段和冷却阶段的晶体热模型,引入变热传导系数对方程进行求解,分别得到LD单端泵浦和冷却时热容激光器温度场的表达式。分析了不同的光斑半径、泵浦时间对晶体温度场的影响。计算结果表明:当泵浦功率为60W、光斑半径为800μm、超高斯阶次为3的脉冲激光二极管对晶体进行泵浦时,在将Nd∶YAG晶体的热导率视为常量和变量的情况下,晶体在泵浦端面获得的最大温升分别为149.93℃、180.18℃。激光晶体的尺寸为(20×20×10)mm3,掺钕离子为1.0%。     

BBO晶体四倍频全固态小功率紫外激光器

 利用KTP晶体和BBO晶体,进行了激光二极管泵浦的Nd:YVO₄声光调Q激光脉冲四倍频实验。在不同绿光功率入射时,获得光束的束腰半径和紫外转换效率的依赖关系:当绿光功率为1.10 W,束腰半径为12.4 μm时,得到了210 mW的准连续266 nm紫外脉冲输出,四倍频转换效率为19.1%。实验还对紫外远场光斑分别在o光振动面和e光振动面内进行分析,指出了BBO晶体在该两平面内不同的倍频接受角是造成椭圆形紫外光斑和主光斑附近明暗条纹的主要原因。     

泵浦光聚焦特性对高重频1064 nm被动调Q激光器的影响

研究了泵浦光聚焦特性对被动调Q激光器输出激光特性的影响。使用10 W激光二极管(LD)和焦距为4 mm的耦合聚焦镜,在不改变LD和谐振腔结构与间距(15 mm)的情况下,选取5个耦合聚焦镜位置,研究对应泵浦光聚焦特性对输出激光特性的影响,特别是对输出脉冲稳定性的影响。泵浦功率为3.550 W时,相较于其他耦合聚焦镜位置,在耦合聚焦镜距离LD 7.50 mm处,被动调Q激光器实现了更高重复频率(160 kHz)、更高平均输出功率(360 mW)、更高单脉冲能量(2.250 μJ)、更低时域抖动(120 ns)的稳定脉冲输出。实验数据说明,耦合聚焦镜距离LD 7.50 mm处,泵浦光聚焦光斑与谐振腔基模光斑的匹配程度较好。理论计算得出,耦合聚焦镜距离LD 7.50 mm时,谐振腔基模光斑尺寸与泵浦光聚焦光斑束腰尺寸的比值为0.854,该比值对今后开展高重频被动调Q激光器相关研究具有一定的借鉴意义。     

直接水冷的Yb∶YAG薄片激光器系统设计与实验研究

设计了一台二极管泵浦的具有新型四通泵浦结构及接触式水冷装置的Yb∶YAG薄片激光器.激光泵浦源采用中心波长为940nm的二极管激光器,利用多模光纤进行耦合输出.YAG晶体Yb3+离子掺杂浓度为10%,几何尺寸为直径10mm,厚度500μm.激光晶体的散热装置采用自来水直接冷却,自来水通过铜热沉中打通的V型槽与薄片晶体直接接触.泵浦耦合系统采用聚焦透镜和一对直角棱镜的组合实现四通泵浦,聚焦透镜规格为直径50mm,焦距50mm.模拟了谐振腔的稳定性及不同腔长条件下所对应的激光光斑半径,设计了不同腔型的Yb∶YAG薄片激光器.在F-P腔中采用透过率为5%的输出耦合镜,获得了最高功率为3.28W的1 031nm连续激光输出,光束质量因子M2x=1.79,M2y=1.86,斜效率为20.5%.     

热效应不敏感的Z型全固态绿光激光器设计

为构建LD泵浦Nd∶GdVO4/KTP腔内倍频热效应不敏感的激光器系统,提高绿光激光的热稳定性,利用基于传播圆变换理论的Z型腔图解分析方法,得到光斑半径w2、w3随热动力参数1/ft的变换关系,利用Mathematics编程软件计算得到了具有激光晶体热透镜不敏性的Z型折叠腔参数。当激光器腔长参数为170mm, 523mm和152mm时,在20.3W的注入泵浦功率下获得了2.72W的531.5nm连续绿光激光输出,实现光 光转换率13%。通过传播圆变换理论图解分析方法的理论计算和实验研究,发现在1/ft小于0.25cm-1的情况下,该腔在激光晶体和倍频晶体处的光斑大小稳定,热效应不敏感,像散不明显。     

LD端面泵浦变热导率方形Yb∶YAG微片晶体热效应

针对激光二极管端面泵浦方形Yb∶YAG微片晶体产生的热效应问题,运用半解析方法计算该晶体的温场分布。根据连续LD端面泵浦方形Yb∶YAG微片晶体的工作特性,建立符合实际工作情况的热模型,构造初始条件和边界条件。同时考虑到晶体的热导率是温度的函数,并结合牛顿法求解热传导方程,得到晶体温度场的一般解析表达式。定量分析了不同的泵浦功率、超高斯阶次、光斑半径、晶体厚度因素对变热导率方形Yb∶YAG微片晶体温度场的影响。结果表明:使用泵浦功率为80 W、超高斯阶次为1、光斑半径为400 m的泵浦光对含方形Yb∶YAG微片晶体质量分数为8.0%、晶体的尺寸为431 mm3进行泵浦,将晶体的热导率视为常量和变量时,泵浦端面获得的最大温升分别为41.25 ℃和52.14 ℃。研究结果对减小全固态Yb∶YAG晶体的热效应问题具有指导意义。     

Laser diode array pumped Yb:YAG/BIBO 515 nm thin disc laser with four-pass optical coupling system

We presented a new simple flat-concave cavity system to produce compact and low-cost 515 nm laser, and the validity has been demonstrated. The Yb:YAG crystal with 10% concentration was 300 μm thickness and 10 mm in diameter. The four-pass optical coupling system was well designed with two spherical imaging mirrors (ϕ = 30 mm, R = 50 mm). Taking into account mode matching, the pump-spot radius in the laser crystal was calculated by LightTools software. The 2 × 2 × 1.5 mm³ BIBO crystal cutting at a type-I phase-matching direction of (θ, φ) = (166.8°, 90°) was employed. With 4.4 W incident power, the maximum output power of 14.3 mW at 515 nm was obtained without optimization of soldering technique, and the single-frequency phenomenon was first observed when the output power was 3 mW.     

300 W continuous-wave operation of a diode edge-pumped, hybrid composite Yb:YAG microchip laser

300 W continuous-wave operation of a diode edge-pumped, hybrid (single-crystal/ceramic) composite,Yb3+:YAG microchip laser with a 5 mm diameter and 300 microm thickness single-crystal core uniformly bonded to a water-cooled heat sink by a new Au-Sn soldering system has been demonstrated. The beam quality factor M2 follows the mode mismatch between the core and the fundamental mode and was improved to 17 with a maximum output power of 230 W. A thermally induced convex mirror with a spherical radius of curvature ranging from -2.5 to -1.5 m was observed; the radius of curvature decreases through thermal deformation of the microchip as the pump power increases.     

Scalable concept for diode-pumped high-power solid-state lasers

A new, scalable concept for diode-pumped high-power solid-state lasers is presented. The basic idea of our approach is a very thin laser crystal disc with one face mounted on a heat sink. This allows very high pump power densities without high temperature rises within the crystal. Together with a flat-top pump-beam profile this geometry leads to an almost homogeneous and one-dimensional heat flux perpendicular to the surface. This design dramatically reduces thermal distortions compared to conventional cooling schemes and is particularly suited for quasi-three-level systems which need high pump power densities. Starting from the results obtained with a Ti:Sapphire-pumped Yb:YAG laser at various temperatures, the design was proved by operating a diode-pumped Yb:YAG laser with an output power of 4.4 W and a maximum slope efficiency of 68%. From these first results we predict an exctracted cw power of 100 W at 300 K (140 W at 200 K) with high beam quality from a single longitudinally pumped Yb: YAG crystal with an active volume of 2 mm³. Compact diode-pumped solid-state lasers in the kilowatt range seem to be possible by increasing the pump-beam diameter and/or by using several crystal discs.     

Efficient High-Power Ho:YAG Laser Pumped by Dual-End-Diode-Pumped Tm:YLF Laser

We report a Ho:YAG (Ho-doped yttrium aluminum garnet) laser pumped by a dual-end-diode-pumped Tm:YLF (Tm-doped yttrium lithium fluoride) laser to obtain an efficient experimental device with high output-power characteristics. We study the influence of the specific values of the output coupling mirror transmittance, the resonant cavity length, and the radius of curvature of the output coupling mirror on the Ho:YAG laser output characteristics. Under optimum experimental conditions, under which the output coupling mirror transmittance was 30%, the resonant cavity length was 25 mm and the output coupling mirror radius of curvature was 300 mm, and the maximum pumping power of the dual-end-diode-pumped Tm:YLF laser was 15.2 W. We obtain an efficient high-power 2.122-μm laser output of 7.98 W from the Ho:YAG laser. The optical-to-optical conversion efficiency is 52.5%, and the beam quality factor figures are M _x ² ?=?2.89 and M _y ² ?=?2.97.     

Efficient tunable Yb:YAG ceramic laser

A high-power efficient ceramic Yb:YAG laser was demonstrated at a room temperature of 20 °C with an Yb concentration of 9.8 at.%, a gain medium of 1 mm, a pumping power of 13.8 W, an output coupler of T = 10%, and a cavity length of 20 mm. A 6.8 W cw output power was obtained with a slope efficiency of 72%. The ceramic Yb:YAG laser exhibited a continuous tunability in the spectral range of 63.5 nm from 1020.1 to 1083.6 nm for T = 1% at a maximum output power of 1.6 W. To the best of our knowledge, this is the first study of the tunability of ceramic Yb:YAG lasers, except crystal Yb:YAG studies.     

High power laser operation with crystal fibers

We present the very last results on the development of high-power lasers with crystal fibers in Nd:YAG and in Yb:YAG grown by the Micro-Pulling Down technique. An overview of the main optical properties of the grown crystal fibers is given as well as the principles of the diode-pumped systems are developed. The average output power obtained with those materials reaches now several tens of watts in the CW regime and in high repetition rate Q-switched operation. Pulses with an energy of several millijoules have been obtained with pulse durations from 10 to 20 ns and peak powers from 100 kW to 350 kW. In each case, the measured M ² quality factors remained in the range 2.5 to 5. In addition, the first demonstration of high-power laser emission with an Yb:YAG crystal fiber of 0.4 mm in diameter is reported. In this case, we obtained an output power of 27 W at 1030 nm under 100 W of pump power at 940 nm in CW regime. To our knowledge, those results represent the highest powers ever generated with crystal fibers obtained directly from the growth. We finally conclude this work by exposing the potential of crystal fiber lasers for a new generation of high-power laser systems.     

激光二极管端面泵浦Yb:YAG圆棒热效应研究

基于激光二极管端面泵浦Yb∶YAG棒工作特点的分析,提出了端面绝热、周边恒温的激光晶体热分析模型,采用了一种新的热传导方程求解方法,得到了超高斯光束端面泵浦Yb∶YAG棒温度场的一般解析表达式。同时分析了不同阶次、不同光斑半径、不同功率超高斯光束以及晶体参数改变时对于Yb∶YAG棒温度场分布的影响。研究结果表明,若准直聚焦到Yb∶YAG棒泵浦面42.5W的光束具有4阶超高斯强度分布时,掺Yb3+质量分数为10.0at.%、长度为2.5mm、半径为2mm的Yb∶YAG棒的泵浦面获得74.20℃的最高温升。新的热传导方程求解方法在研究激光棒温度场分布方面具有计算量小、精度高等特点。研究结果对减小激光晶体的热效应,提高全固态Yb∶YAG激光器性能提供了理论依据。     

Enhanced performance of thin-disk lasers by pumping into the zero-phonon line

Pumping Yb:YAG or Yb:LuAG into the zero-phonon line at 969?nm instead of using the common pump wavelength of 940?nm reduces the heat generation by 32%. In addition to the 3% increase of the Stokes efficiency, this significantly reduces the diffraction losses caused by the thermally induced phase distortions leading to a remarkable increase of the overall efficiency especially of fundamental-mode thin-disk lasers. Using this pumping scheme in an Yb:LuAG thin-disk laser, we achieved 742?W of nearly diffraction limited (M²≈1.5) output power at an unprecedented high optical efficiency of 58.5%. For multimode operation (M²≈15) the maximum optical efficiency of an Yb:YAG thin-disk laser was increased to 72%.     

Optimal design for a diode-pumped high-power high-efficiency high-beam-quality laser

We have demonstrated and analyzed a high-power high-efficiency high-beam-quality continuous-wave (cw) Yb:YAG laser, which is directly pumped into the upper lasing level by a fiber-coupled laser diode with a center wavelength of 969 nm. To achieve high efficiency and high beam quality simultaneously, we carried out a series of comparing experiments by changing the laser-medium length and pump-beam waist radius. From the cw Yb:YAG laser with a 5.0-at.%-Yb³⁺-doped and 5-mm-long crystal, an output power of 19.0 W has been obtained for a pump-beam waist radius of 138 μm. The maximum slope efficiency and optical-to-optical conversion efficiency are 78.9% and 55.3%, respectively. The M² factors of the laser beam are 1.33 in the vertical direction and 1.82 in the horizontal direction.