束旋转90°对束变换环孔腔输出性能的影响

 使用积分方法和差分方法结合的快速计算方法，在实际燃烧驱动氟化氢化学激光器增益介质沿径向分布不均匀的情况下，考虑在光束变换环形孔径激光谐振腔的紧束段引入光束旋转90°对其输出性能的影响。计算结果显示：在无腔失调的情况下，在紧束段引入光束旋转对束变换环孔激光谐振腔输出功率及光束质量的改善并不显著；在存在腔失调的情况下，紧束段光束旋转对于输出功率和光束质量的改善有显著效果。     

Long-range propagation of annular beam for lidar application

Long-range propagation characteristics of an annular beam were examined from the viewpoint of lidar application. The annular beam permits to use a reflecting telescope for transmission and improves the transmission efficiency because it can pass through the telescope without the obstruction of the telescope’s secondary mirror. As the annular beam can enlarge up to the telescope diameter, it can be eye-safe and its divergence is also reduced.The annular beam generated by a couple of Axicon prisms; conical prisms, transforms its beam shape into the central peak narrow beam; nearly non-diffractive beam, through the far-field propagation. We evaluated how the central peak intensity and its width of the transformed beam change in long-range of 3-100 km. The difficulty of the optical arraignment and the requirement of the beam quality to obtain the enough performance of the beam shape transformation were also examined theoretically and experimentally for the lidar application. The stability of the transformed beam was also confirmed in the atmospheric fluctuation.     

环状连续强激光下光学薄膜的瞬温和热畸变

详细研究了非冷却光学薄膜元件在环形激光光束辐照下的瞬态温度分布和随后的热畸变，并且用泰曼干涉仪实际测量了连续波氧碘激光辐照各种非冷却光学元件的热畸变量并与理论计算相比较，分析结果表明理论和实验相一致。     

环形分布激光束引起光学窗口镜热变形理论分析

 用有限Hankel变换就常见的环形分布激光束情形，推导得到了激光束辐照透过窗口镜引起热传导温度场和热变形分布的理论解，以此计算结果与实验值相比较，分析了白宝石、石英两种窗口镜在激光辐照下的热变形情况。分析结果表明，在激光束辐照的4s时段内，温升场主要集中在激光束辐照的环形区内，在镜面内远未拉平，由此引起的厚度方向热膨胀变形也很不均匀。材料对激光的吸收系数和热膨胀系数以及热扩散率分别是决定热变形量值大小和空间分布的最主要的物性参数。     

Thermal effects of the diode end-pumped Nd:YVO4 slab

The thermal effects of the diode end-pumped Nd:YVO₄ slab laser crystal are investigated both analytically and numerically. The theoretical model is established with considering the divergence of the pump beam in the slab. A detailed theoretical analysis of the temperature, stress and the focal length of thermal lens are presented. Using 3D finite element analysis, an accurate numerical solution based on the theoretical model is achieved. Our analysis includes the thermal fracture damage of the thermally and optically anisotropic slab and the predicated values are compared with the experimental results.     

Thermal stress effects of the diode-end-pumped Nd:YLF slab

The thermal stress effects of the diode-end-pumped Nd:YLF slab laser crystals are numerically investigated. The theoretical model is established by considering the divergence of the pump beam in the slab and the additional heat generated in the upconversion. Using the three dimensional finite element analyses, accurate numerical solutions based on the theoretical model are achieved. Our analyses focuses on the thermal fracture damage of the Nd:YLF slab under both the lasing and non-lasing conditions, and the predicted values are compared with the experimental results.     

Thermal management of GaInNAs/GaAs VECSELs

Different methods used to reduce temperature increase within the active region of vertical-external-cavity surface-emitting lasers (VECSELs) are described and compared with the aid of the self-consistent thermal finite-element method. Simulations have been carried out for the GaInNAs/GaAs multiple-quantum-well (MQW) VECSEL operating at room temperature at 1.31 μm. Main results are presented in form of ‘thermal maps’ which can be simply used to determine maximal temperature of different structures at specified pumping conditions. It has been found that these maps are also appropriate for some other GaAs-based VECSELs and can be very helpful especially during structure designing. Moreover, convective and thermal radiation heat transfer from laser walls has been investigated.     

Bessel光束经椭圆环形孔径后的衍射光场

基于菲涅耳衍射积分理论及硬边孔径的复高斯函数展开法导出了Bessel光束经椭圆环形孔径后的光场表达式, 数值模拟了其光场的强度分布. 研究了Bessel光束经椭圆环形孔径后的光场变化及其传播过程; 在实验上利用轴棱锥输出的近似无衍射Bessel光, 通过椭圆环形孔径, 使用电荷耦合器件拍摄得到不同传播距离处的光强分布. 理论结果和实验结果均表明无衍射光束经椭圆环形孔径后会产生空心光束.     

平顶光端面抽运DPL中热效应对输出功率的影响

用平顶光束描述由多根光纤紧密排列耦合并经透镜整形后的抽运光分布，给出了平顶光束的光强分布，对晶体热效应引起的热致衍射损耗随抽运功率和抽运光束半径的变化规律进行了数值计算，讨论了晶体热效应引起的热致衍射损耗对基横模高斯光束输出功率的影响，并实验验证了基横模高斯光束输出功率随抽运功率的变化规律．结果表明：热致衍射损耗使基横模高斯光束输出功率明显降低．随着抽运光束半径的增大，热致衍射损耗减小，对基横模高斯光束输出功率的影响就减小；抽运功率越大，热致衍射损耗越大，对基横模高斯光束输出功率的影响就越大．     

A High‐Efficiency All‐Fiber Laser Operated in High‐Order Mode using Ring‐Core Yb‐Doped Fiber

An all‐fiber laser generating a cylindrical vector beam is proposed and demonstrated using a home‐made ring‐core Yb‐doped fiber (RC‐YDF). In the RC‐YDF, not only annular doping but also ring‐type beam pump is realized. This is believed to be the first report describing the realization of annular doping and ring‐type beam pump in active fiber simultaneously, which can enhance the efficiency for high‐order mode oscillation. This laser operates in the high‐order mode stably with a slope efficiency of as high as 55.7%. Cylindrical vector modes can be obtained easily through adjusting the polarization controller. This work may have great potential for providing high‐efficiency and high‐power cylindrical vector beam and vortex beam sources.     

Magneticresonant three dimensional kinetic theory of the free electron laser with waveguide cavity

Vlasov kinetic theory of the free electron laser employing waveguide frifting tube and helical pump is presented. Distinct from the former theories this theory has (1) taken into account the 3-d structure of the scattering field; (2) applied the plasma kinetic theory, which is more accurate than the other methods, to analysing the effect of the longitudinal. field; (3) taken account of the influence of the annular structure of the beam. The magnetic resonant effect appearing when the cyclotron frequency of electrons approaches the effective frequency of the magnetic pump is analysed and the growth rate formula in the linear regime derived. Results show that on taking into account the 3-d structure of the field and beam, one cannot arbitrarily choose the radius of the hollow beam, or else within certain range the instability may disappear altogether. Lastly, the equation for determination of the optimum beam radius is given and the possibility of raising growth rate by operating in high order modes shown.     

环形光束锥形衍射出射光场偏振特性及光场调控

环形光束的锥形衍射效应对于微粒的操控具有重要的应用价值.本文建立了环状高斯光束的锥形衍射模型,并基于Berry理论给出了线偏振态下环形光束锥形衍射出射光场的计算公式.理论仿真了环状光锥形衍射出射光场的偏振特性,得出环光锥形衍射出射光场的内、外亮环具有相互正交的偏振分布特性.搭建了线偏振态下环状高斯光锥形衍射的实验系统,实验验证了出射光场的偏振特性.针对环形光束锥形衍射出射光场具备的偏振特性,设计了一种组合偏振片,理论和实验研究了该组合偏振片对环光锥形衍射出射光场的调控.结果表明,随着组合偏振片方位角的变化,锥形衍射出射光场的内、外环强度发生周期性的变化.     

风对光束控制系统内热效应的抑制作用

 用光强沿x轴方向呈线性变化的方形环状光束模拟高功率激光，利用自编四维仿真程序对高功率激光在光束控制系统中的传输作了详细的数值计算研究。结果表明：热效应使远场光束的峰值光强和可聚焦能力下降。入射光强的非均匀分布进一步降低峰值光强和可聚焦能力，导致远场光束重心和峰值光强位置移动，并产生像散。光束的非均匀程度越高，远场光束质量越差。横向风和轴向风对热效应均有抑制作用。然而，轴向风不会引起远场光束重心偏移和像散，但是轴向风比横向风建立稳态所用时间更长。     

非稳腔输出环状激光束的传输特性

本文从菲涅耳衍射积分公式出发研究了激光器非稳腔输出环状光束在空间的传输规律.由轴上光强的极值点位置给出了划分非稳腔传输空间的近场、中场和远场区域公式.理论计算结果表明,非稳腔输出端环状光束在中场区域激光能量逐渐向轴心方向转移,而在远场变为爱里型圆盘状光束的过程.在非稳腔脉冲TEA CO_2激光器上测得的实验结果与理论计算结果很好地符合.     

环状光纤单模条件和远场能量分布特性

基于弱波导近似,通过数值计算得出了环状光纤保持单模状态时对芯-包层折射率差值和导光层厚度的要求,同时讨论了这些设计参数对远场能量分布的影响。计算结果表明:当环状光纤工作在单模状态时,从光纤出射的环形光束衍射至远场时形成一个中央亮斑,具有很高的能量集中度。此外,减小芯-包层折射率差值与导光层厚度有利于进一步减小远场衍射的光斑宽度。     

Influence of spherical aberrations on the performance of dynamically stable resonators

Spherical aberrations of thermal lens of the active media are severe when the solid state lasers are strongly pumped. The aberrations influence the mode profile, the diffraction loss, the output power and other laser beam properties, especially for a dynamically stable resonator with large TEM₀₀-mode volume. Self-consistent modes in a resonator with aberrations are calculated using Fox-Li diffraction iterative algorithm. There are side lobes with the fundamental mode when the spherical aberration is introduced, hence the beam quality is deteriorated. The calculated results agree well with the experimental data. The beam filling factor plays an important role in the design of a laser system. The optimum value of the beam filling factor should be determined by the experimental results according to the spherical aberration effect.     

非均匀激光辐照下硅镜热变形对光束传输特性的影响

 使用有限元法计算了硅镜在DF化学激光器非稳腔输出的中空非均匀激光辐照下镜面温升和反射面面形随时间变化的特性,使用65阶Zernike多项式对镜面面形进行了曲面拟合,使用光线追迹的方法计算了平行光束经不同数量硅镜反射后的光束波前分布PV值、Strehl比和Zernike像差系数随时间变化的特性。计算结果表明：在典型的DF激光器输出的中空方形光束辐照下,硅反射镜的热变形将使反射光束产生波前畸变,波前畸变中,y方向像散项占据主要地位,其次是离焦项;随着激光系统中反射镜面数量的增加,高阶像差系数将逐渐增大,且波前PV值与反射次数成线性关系。     

AlInGaAs垂直谐振腔顶面发射半导体激光器横向温度效应的解析热模型及其表征

依据增益导波垂直谐振腔顶面发射半导体激光器热区特点与室温连续波运行条件建立了一个优化的全解析热模型，对AlInGaAs/AlGaAs垂直谐振腔激光器的横向温度效应进行了详细的解析计算分析，其完全的解析表达展示了更加清晰的横向热场物理图像，对于器件内部热场变化规律的理论预期与实验结果完全符合. 该解析模型及其结果对于研究热稳态下的垂直谐振腔激光器热动力学特性，优化器件结构和控制激光器的阈值电流与功率温度饱和效应，特别是二维面阵器件中的横向热叠加效应提供了一个有用的工具. 关键词： 半导体面发射激光器 热效应 解析计算模型.     

环形管环状流临界热负荷解析模型

根据环形管内流动与传热的特点,重新定义了环形管的水力直径和热周直径,基于圆管环状流CHF解析模型,得到了环形管内环状流临界热负荷解析模型。该模型可以预测环形管内沸腾两相流环状流时在不同加热方式下发生的临界热负荷,加热方式包括有内侧加热、外侧加热、两侧同时加热等。数值预测结果与文献数据比较表明本文的解析模型在P=0.57-15.01.MPa,G=198-3789.5 kgm-2s-1,xc=0.068-0.855,L/Dhe=19.3-539.5范围内预测良好。     

环形区域上Zernike模式法波前重构

 针对激光技术领域常见的环形激光光束,利用圆域Zernike多项式和环域Zernike多项式进行模式法波前重构,结果显示,如果环形激光光束波前相位畸变主要由低空间频率成分组成,则可以直接利用圆域Zernike多项式进行波前重构;如果环形激光光束波前相位畸变含有较多的高阶频率成分,则利用环域Zernike多项式进行波前重构。