固态热容激光器3维瞬态热畸变模拟分析

 根据固态热容激光器的动态工作特性,考虑热力学参数与温度的关系,采用3维有限差分方法模拟分析了薄片热容激光器的3维温度和热应力分布随时间的变化关系。计算了热容激光器的热畸变和退偏损耗随时间的动态变化规律,并与采用连续水冷却方式工作的圆棒激光器的热畸变特性做了比较。模拟结果显示,形变是引起波前相位畸变的主要因素,退偏损耗随泵浦时间增加和泵浦功率增大而非线性增大。     

Semianalytical thermal analysis of rectangle Nd:GGG in heat capacity laser

Based on the theory of anisotropy semianalytical thermal analysis, the temperature field of rectangle Nd:GGG heat capacity laser crystal is investigated. Through an analysis of the working characteristics of the heat capacity laser crystal, a thermal model of heat capacity laser crystal is established. Using a new method for the anisotropic medium heat conduction equation, a temperature field expression of rectangle Nd:GGG heat capacity laser crystal for pumping stage and cooling stage is obtained, respectively. These results show that when using the output power of 300 W LD end-pumped rectangle Nd:GGG crystal for 10 seconds, the maximum temperature rise in the center of the pump face is 180.18°C, and after stopping pumping for 100 seconds, the maximum temperature rise drops to 0.74%. These results from this work provide a theoretical basis for the optimized design of a LD end-pumped heat capacity laser.     

片状热容激光器热效应有限元分析

 基于激光介质的非均匀内热源模型，利用有限元数值方法，模拟计算了热容模式下高功率激光二极管阵列(LDA) 重复脉冲泵浦片状激光介质的瞬态温度分布和热应力分布及其波前畸变和应力双折射。结果表明:热容模式下，当增益介质不能够被全口径泵浦时，也会出现严重的热效应，介质的表面靠近边缘处会出现大的拉应力集中，介质表面的最大轴向位移和最大拉应力随泵浦光斑尺寸缩小而增大；而当全口径泵浦时，介质表面热形变大大减弱，较小的拉应力存在于介质内部，而且泵浦光斑和介质的几何形状对热分布有很大影响。结果还表明，介质片表面变形和热光效应是产生波前畸变的主要原因，而热应力双折射产生的附加相移与激光介质的切割方向有关，它对光束产生较大的退偏作用，从而影响激光器的输出性能。理论模型得到了实验结果的验证。     

固体热容激光器冷却方式的数值模拟

 固体热容激光器连续运转一段时间后，需要进行冷却，以进行下一次运转，因此冷却速度直接影响着热容激光器运转的效率和实用性。从热传导方程出发，以沉积热为内热源模型，利用有限元分析方法对激光二极管阵列从4个方向对称泵浦的板条Nd:GGG激光介质的温度场和和热应力场进行了数值模拟。并对冷却阶段分别采用过冷气体、水循环、喷雾、相变冷却方式时的介质温度和应力随时间变化过程进行了模拟。结果表明在相同条件下采用相变冷却方式能在较短时间内将介质冷却到初始温度。     

LD阵列侧面泵浦棒状激光介质内的光场研究

建立了LD侧面泵浦激光介质内的光场分布数值模型。通过光线追迹方法,简化了介质对泵浦光折射的计算方式。利用Matlab软件数值模拟了泵浦光在介质内的归一化分布。提出获得高质量、高能量的激光输出参数的选取原则。当LD的束腰半径为1μm、LD的数量为40个、介质的半径为1.5mm、发光面到介质的泵浦距离为0.5mm、介质吸收系数在2cm-1～6cm-1之间时,泵浦光在激光介质内的增益分布较好。     

斜抽运无机液体激光器的流场热分布

激光二极管斜抽运的多增益段串接的液体激光器能够明显地提高激光光束质量、获得较高的输出功率.针对斜抽运子增益段工作时所涉及的流动、传热和壁面耦合,建立了计算子增益段流场热分布的流-热-固耦合模型,应用有限单元法完成了其瞬态流场热分布的数值模拟.该方法排除了不精确的换热系数对计算结果的影响,使得换热系数不再是计算的先决条件,而只是计算结果之一,并且为评价流道形状、流速、吸收系数等因素对流场热的影响,以及进一步改进和控制液体激光介质的流场热分布,提供了可靠的分析方法.数值模拟研究表明:换热系数是空间位置的函数,     

热容激光器激光介质的热力学数值模拟

为模拟激光介质的温度、热应力的分布和变化,建立了激光介质热力学计算模型.该模型从激光介质的瞬态导热微分方程出发,得到沿纵向的热沉积功率密度,并将其作为该微元段的热载荷,加载到该微元段的泵浦区.考虑热容值、热导率、热膨胀系数和弹性模量等与温度的关系,得到激光介质的温度分布和变化,以及热应力的分布和变化.为热容激光器的实验和设计提供参考依据.     

二极管侧面泵浦薄片激光器泵浦均匀性分析

 建立了二极管侧面泵浦复合薄片激光介质Nd:YAG/YAG的数值模型：二极管阵列的快轴垂直于薄片激光介质表面的排布,二极管对称排列在增益介质的周围,从侧面进行泵浦,通过微柱透镜对二极管的快轴进行准直。模拟并实验研究了激光二极管慢轴方向的远场分布特性,结果发现在近距离时激光二极管慢轴方向上的远场分布近似为高斯分布。对于二极管参量,研究发现泵浦二极管越多,增益介质内泵浦光分布就越理想;增益介质吸收系数越小,泵浦的均匀性就越好,但总的吸收效率下降;二极管与工作物质的距离越近,工作物质靠近中心的区域对泵浦光的吸收就越多,但泵浦的均匀性就越差。选用增益介质为Nd:YAG/YAG的复合薄片介质,当掺杂原子分数以及增益介质的吸收系数不同时,发现0.6%掺杂的增益介质(吸收系数为0.24 cm^-1)的泵浦均匀性比1%掺杂(吸收系数为0.51 mm^-1))有明显改善,实验结果与模拟结果一致。     

二极管泵浦Nd:YAG圆片激光技术研究

介绍了热容激光技术的发展历史及现状,介绍了固体激光器热容方式工作的基本原理,报道了二极管泵浦NdYAG圆片激光器热容方式工作的实验结果.用热像仪测量了激光器工作时增益介质通光面上的温度分布特性;采用干涉测量的方法测量了工作中的增益介质的与光束传输方向相垂直的方向上的折射率分布特性;结果表明片状固体增益介质热容方式工作对振荡光束波前畸变影响很小.给出了与光束传输方向相垂直的截面上增益介质的荧光分布.得到输出平均功率达47.5 W,此时的光-光转换效率为17%.     

基于横向热流抑制的半导体激光芯片封装实验研究

为降低半导体激光芯片的慢轴远场发散角,提高其慢轴方向的光束质量,设计了横向热流抑制的封装结构。利用热沉间的物理隔离,削弱了半导体激光芯片慢轴方向上的温度梯度,有效降低了半导体激光芯片慢轴方向的发散角。采用热分析模拟了不同封装结构下芯片发光区的温度分布,并对波长915 nm的窄条宽半导体激光芯片进行封装。实验结果表明,在工作电流15 A,封装在隔离槽长4 mm,脊宽120 μm刻槽热沉上的芯片,其慢轴远场发散角由12.25°降低至10.49°,相应的光参量积（BPP）由5.344 mm·mrad 降低至4.5763 mm·mrad,慢轴方向亮度提升了约5.5%。实验结果表明,横向热流抑制的封装结构可以有效地削弱半导体激光芯片慢轴方向上由热透镜效应引起的高阶模激射,从而降低其慢轴远场发散角。     

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.     

The LD end-pumped Q-switched solid-state laser design software based on the adaptive method

In the LD end-pumped acousto-optic (A-O) Q-switched solid-state laser, according to the requirements of users on the laser peak power, the pulse width, the repetition rate and the beam quality factor M², if the main parameters of the pumping source and the laser resonator can be pre-designed by a software, will effectively guide experiments, and save cost. A kind of laser design software is introduced in this paper, which is based on the adaptive adjustment method and using MATLAB/C mixed programming. According to the user requirements, a compact LD end-pumped A-O Q-switched Nd:YAG laser which peak power is 100-kW-class can be designed and actual outputs can be calculated based on the design results. Drawing the laser pulse waveform, analyzing of the thermal effect in laser gain medium and drawing the temperature distribution map, exporting and saving the data are the additional functions of this software.     

Thermal mode-switching of a passively Q-switched microchip Nd:YAG laser

In the present article, the thermal distribution inside the gain medium of a passively Q-switched microchip laser is modeled and simulated for actual practical values associated with an available microchip laser constructed in our laboratory. The effects of the non-uniform heat distribution on the spectral properties of the output laser beam have been investigated and simulated with the variation of diode-pump power and pulse repetition rate. It is observed that the gain bandwidth as well as Optical Path Difference (OPD) values of the propagating pulses are significantly decreased, while the Nd:YAG chip is cooled down to a certain value. The validity of the utilized model is checked by setting and characterizing the spectral properties of a fabricated laboratory microchip laser under different heating conditions. It is verified that when the temperature of the gain material is changed by an electronically controlled Peltier device, the spectrum of the output laser beam can be switched between single- and dual-mode situations. This physical character has shown good agreement between the presented model and obtained experimental results.     

高密度封装二极管激光器阵列

 理论模拟了自制的高效冷却器的散热能力,分析了单元封装结构所需材料的导热特性,获得了高功率二极管激光器在高功率密度、高占空比条件下运行的可行性。改进了高密度封装的关键工艺,热沉金属化层达到了3~5 mm,焊料厚度为4~7 mm,封装间距0.6 mm,采用峰值功率1 kW的背冷式叠阵二极管激光器。实验测试结果表明:封装的二极管激光器叠阵单元的整体封装热阻为0.115 ℃/W,有良好的散热能力;该叠阵模块在电流为100 A、占空比15%时,输出峰值功率为986 W,峰值功率密度达到1.5 kW/cm2,平均每个板条的斜效率为1.25 W/A,激光器阈值电流为20 A左右。     

CW-COIL输出功率与输出孔径及光轴位置之间的依赖关系

 氧碘化学激光器由于复杂的动力学因素,激光介质的增益分布通常是不均匀的,这就使得激光输出功率并不完全随着激光输出孔径成线性增加,也由于这种增益分布的不均匀性,即使在激光输出孔径不变的情况下,激光输出功率也会随着光轴位置的改变而发生变化。为此,在激光器工作参数固定条件下,通过实验描述了激光输出功率与激光输出孔径及光轴位置之间存在着的一定的依赖关系。     

被动锁模Yb3+光纤环形腔激光器的研究

 采用974 nm半导体激光器作为泵浦源，超高掺杂Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到稳定的ps量级锁模光脉冲。泵浦功率220 mW时，激光器锁模阈值功率150 mW，输出功率26 mW，锁模光脉冲中心波长1 046 nm，3 dB带宽6.01 nm，20 dB带宽16 nm，脉宽22 ps，重复频率20 MHz。与同类光纤激光器相比，该激光器输出功率高，具有更好的稳定性。     

Jet-type, water-cooled heat sink that yields 255-W continuous-wave laser output at 808 nm from a 1-cm laser diode bar

A newly designed jet-type, water-cooled heat sink (the funryu heat sink, meaning fountain flow in Japanese) yielded 255-W cw laser output at 808 nm from a 1-cm bar made from InGaAsP/InGaP quantum-well active layers with a 67% fill factor [70 quantum-well laser diode (LD) array along the 1-cm bar]. A funryu heat sink measuring 1.1 mm in thickness gave the LD 0.25 degrees C/W thermal resistance, one of the lowest values achieved with a 1-cm LD bar. Over a short period of operation, the device reached a maximum cw power of 255 W. To the best of our knowledge, this is the highest power ever achieved in 808-nm LD operation. In the future, the funryu heat sink may be capable of 80-W cw operation over an extended lifetime of several thousand hours.     

Microstructure, hardness and stress in melted zone of 42CrMo steel by wide-band laser surface melting

Using laser surface melting (LSM) of a roller, to obtain the desired distribution of the microstructure, hardness and residual stresses with minimum distortion, is essential in order to improve machining efficiency and to achieve reliable service performance. In this study, a 3D finite element model has been developed to simulate the wide-band LSM process and predict the thermal and mechanical properties in the melted zone. The microstructure evolution, hardness distribution and stress field in the melted zone with different laser power were simulated. With the increase of the laser power from 3000 to 3800 W, the width and the depth of the laser melted layer increase, while the laser power has a little effect on the martensite contents, which exceed 90% in the melt-hardened zone. It greatly affects the mechanical properties in the melt-hardened zone with its volumetric expansion effect and the hardness increases by 2-3 times. The residual stress distributed within the melt-hardened zone is always of the compressive type. The amplitude of compressive stress exists in the transition region, and the amplitude of von Mises stress within the heat affected-zone (HAZ) decreases with the increase in laser power. The accuracy of the developed finite element simulation strategy is validated for phase proportion and hardness distributions through the wide-band LSM on roller steel with proper instrumentation for data measurement. This agreement is encouraging.     

二极管泵浦300 W热容固体激光器

开展了热容二极管泵浦固体激光器理论和实验研究,针对热容工作模式下工作物质的激光特性进行了初步分析,数值模拟了激光介质增益分布及温度场、应力场分布,初步完成了热容激光器实验平台的建立,在平均泵浦功率1.25 kW的激励条件下获得了大于300 W的激光输出,连续出光时间为5 s,占空比为15%,光-光转换效率约为25%.     

低功率激光热透镜效应的模拟及研究

与高功率激光相比,低功率激光更安全,其热透镜效应对激光功率变化更敏感,更适合用于实验教学.本文利用有限元法模拟低功率激光的热透镜效应,模拟介质温度场和等效热透镜焦距,定量探究低功率激光热透镜焦距与激光功率以及介质热吸收率、厚度的关系.模拟结果与实验数据符合良好,为探究低功率激光热透镜效应实验提供理论依据.