Influences of pump beam distribution on thermal lensing spherical aberration in an LD end-pumped Nd:YAG laser

A numerical investigation is made on the thermal lensing and spherical aberration effect in an LD end-pumped Nd:YAG laser. Based on the finite element method (FEM), the laser rod temperature distribution is calculated and the focal length of the thermal lens is deduced, the influences of pump beam on the thermal lensing spherical aberration are mainly studied. The results show the thermal lens which focal length varied with the radial coordinate r is not an ideal lens. Given the heat dissipation boundary conditions, the radial dependent focal length will be shortened when the pump power raised or the waist radius of the pump beam reduced, meanwhile the radial differences of the focal length will decrease when the pump power increased. For a Super-Gaussian profile pump beam, the higher the exponent number, the more similar to flat top the pump beam is, and the less the radial differences of the focal length are.     

Thermal lens determination of LD end-pumped solid-state laser with stable resonator by slit scanning method

A simple method to determine the thermal focal length of LD end-pumped solid-state laser with stable resonator is presented. The M² factor describing the quality of the beam can be obtained by scanning a slit through the multi-mode Gaussian beam field. The waist width of the beam and the corresponding TEM₀₀ under the same parameters of laser are then deduced through the law of multi-mode Gaussian beam propagation. Based on the standard matrix theory of stable resonator, the thermal focal length of the gain medium can be easily achieved. To show the application of this approach, the thermal focal length of an LD pumped Nd:YVO₄ laser is measured and the experimental results are in agreement with the theoretical prediction.     

薄片激光器热效应及其对输出功率的影响

建立了光强分布为高斯型的抽运光端面单程抽运时薄片激光器的温度模型, 实验测量了不同抽运功率下薄片介质表面的 温度分布、温度随时间的变化特性以及介质表面的温度差. 采用Hartmann法测量了薄片介质的热焦距. 考虑热焦距随抽运功率的变化, 基于四能级系统薄片激光器的速率方程组, 建立了薄片激光器热效应对输出功率影响的物理模型, 薄片激光器输入-输出功率曲线与实际相符. 所得结果对薄片激光器的设计和优化具有一定的指导意义.     

激光热透镜焦距测量实验及其公式改进

通过平平非稳腔法对激光热透镜焦距进行了实验测量,研究了不同抽运光束腰位置对热透镜焦距的影响.从理论上引入抽运光远场发散角和束腰位置,对端面抽运激光晶体热透镜焦距公式进行了改进.     

二极管端面抽运的固体激光放大器自身热透镜焦距测量

通过分析激光经过热透镜后光束半径的变化，提出了利用放大器测量热透镜焦距的方法.根据激光束传输与变换理论，得到了热透镜焦距的表达式，并分析了其前提条件和近似偏差.最后，基于上述理论分析，测量了激光二极管端面抽运Tm,Ho∶GdVO₄放大器的热透镜焦距. 关键词： 热透镜焦距 固体激光 激光束传输与变换     

LDA侧面抽运棒状激光器热透镜效应的有限单元法分析

建立了激光二极管阵列端面抽运棒状激光介质的数值模型.考虑到介质与空气的对流换热和介质的热力学参量随温度的变化,根据经典热传导方程和热弹性方程,运用有限单元法,得出了棒状介质内瞬态温度、热应力和应变的分布.分析了热透镜焦距随抽运功率的变化规律,所得的规律与有关文献相符合.理论分析结果可为激光二极管阵列抽运固体激光器的结构优化设计和实验提供理论参考.     

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.     

A simple method to determine the thermal focal length of solid-state lasers with rate equation

A simple method to measure the thermal focal length of solid-state laser with rate equation was presented. By measuring the output beam power of lasers, the beam waist of oscillating wave can be deduced from rate equation under the stable oscillation condition. Based on the ABCD matrix theory, the thermal focus of the gain medium was easily obtained. The thermal focus of a LD end-pumped Nd:GdVO₄ laser was measured and the experimental results agreed with the theoretical predication.     

Simultaneous self-mode-locking of TEM<Subscript>0,0</Subscript> and TEM<Subscript>1,0</Subscript> modes in a Nd:YVO<Subscript>4</Subscript> laser: Application for measuring the thermal focal length

We demonstrate that the simultaneous self-mode-locking of TEM_0,0 and TEM_1,0 modes can be achieved in a standard end-pumped Nd:YVO₄ laser. With this simultaneous self-mode-locking, the transverse beat frequency can be accurately measured as a function of the absorbed power. We employ the measured beat frequency and the cavity theory to precisely determine the effective focal length of the thermal lens in the gain medium.     

Theoretical investigation on thermal lensing effects of Yb:KY(WO4)2 in diode-pumped lasers

Based on the features of laser diode end-pumped lasers, a thermal model of Yb:KY(WO₄)₂(Yb:KYW) with square cross-section was established. Considering the heat transfer on side faces, the anisotropic of thermal conductivity and the latest reports about thermo-optic coefficient, thermal expansion coefficient and thermal conductivity, temperature distribution, end-pumped face distortion and thermal lens focal length of Yb:KYW were more precisely obtained using finite difference method to solve Poisson equation in a rectangular Cartesian coordinate for the first time. At the pump power of 14 W, the highest temperature located at the center of end-pumped face was 243.8 °C, the highest distortion was 0.28 μm, and the thermal lens focal length was 5.4 cm along z-axis and −4.9 cm along x-axis. The results show that thermal lensing effects in the b-cut Yb:KYW were mainly determined by the anisotropic thermal expansion of Yb:KYW, and further present thermal lensing effects become weaker after considering the heat transfer. This work is significant for compensating the thermal lensing effect and improving the resonator stability of diode-pumped anisotropy crystal lasers.     

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.     

The overall phase shift and lens effect calculation using Gaussian boundary conditions and paraxial ray approximation for an end-pumped solid-state laser

In this work, the inhomogeneous equation of heat conduction was exactly solved by applying inhomogeneous boundary conditions for laser crystals of aspect ratio=1 (aspect ratio=radius of the laser rod/length of the laser rod). We have shown that the paraxial ray approximation leads the solution to be a function ofr ² , that is, the approximation is equivalent to a situation in which a homogeneous pump source is used. The solution was then used to derive expressions for the overall phase shift, focal length of the thermal lens and the end effect induced curvature of the end face. The expressions were then applied to Nd:YAG laser medium. The result shows a meaningful correction of the order of 0.001 cm to the focal length of Nd:YAG rod for 3 W source power and beam waist of 100 μm.     

基于侧面热对流的LD泵浦Yb:KGd(WO4)2热透镜效应研究

基于对LD端面泵浦Yb∶KGW激光晶体工作特点的分析,建立了符合条件的激光晶体热模型.考虑晶体侧面的热对流,运用MATLAB和FORTRAN软件,通过有限差分法求解各向异性介质热传导方程,得到了该晶体的温度场分布、端面热形变分布和不同泵浦功率下的热焦距.结果表明:在泵浦功率为14 W时,泵浦面最高温度达272.8℃、最...     

Diode-pumped orthogonally polarized dual-wavelength Nd3+:LaBO2MoO4 laser

Polarized spectroscopic properties related to 1.07 μm laser operation of a 1.8 at.% Nd³⁺:LaBO₂MoO₄ crystal grown by the Czochralski method were investigated at room temperature. Using a 2.2-mm-thick, Z-cut Nd³⁺:LaBO₂MoO₄ crystal as gain medium, orthogonally polarized dual-wavelength laser at 1,068 and 1,074 nm was first realized in a plano-concave resonator end-pumped by a quasi-continuous-wave 795 nm diode laser. A total output peak power of 1.2 W with slope efficiency of 26 % around 1.07 μm was obtained. The influences of resonator length and pump power on output laser wavelength were also investigated.     

Numerical simulation of end-pumped CW Nd^3＋：GdVO4 laser at 1063 nm

A theoretical model to simulate an end-pumped CW Nd^3＋：GdVO4 laser at 1063 nm is presented. Its essence is to use the propagation equations to demonstrate the spatial evolutions of the pump and the laser powers in the cavity, hence it is applicable to both low and high gain lasers. The simulation results obtained by this model are in good agreement with the experimental observations reported in the literature for a Ti：sapphlre-pumped Nd^3＋：GdVO4 laser. Moreover, some parameters, such as the reflectivity of output coupler, the spot size of laser beam and the crystal length, are discussed with a view to optimizing the laser performance.     

Thermal lens and its effects in copper-vapor lasers

We have analyzed and measured the thermal lens of the copper-vapor laser by considering both its windows and active medium. The equivalent combined focal length varies with operation parameters and it is sensitive to the laser geometry. The results are verified by our measurements on a 20 W device with 35 mm internal diameter tube. The thermal lens effects on the beam properties are analyzed and verified with the experiments for both oscillator and laser chain case.     

高光束质量、高功率稳定性激光器的设计及实验研究

高光束质量、高功率稳定性激光器在激光加工、激光测量等领域具有广泛的用途.为了实现激光器腔内光斑聚焦同时减少色散和体积,人们常常将曲面反射镜用在激光谐振腔中,但光束倾斜入射到曲面反射镜往往会引起像散,从而导致光斑质量恶化,并降低激光器的性能.另一方面,在高功率激光器或超短脉冲激光器中,激光增益介质热透镜焦距的起伏,是导致激光输出功率波动的主要原因之一.针对激光器的像散和功率波动这两个问题,本文提出了一套简单高效的解决方案,在考虑像散补偿和热透镜效应的基础上,基于传播变换圆理论,首次提出一种可实现高光束质量、高功率稳定性激光器谐振腔的设计方法,并对采用该方法所设计出的超短脉冲激光器进行理论与实验研究.研究结果表明,利用该方法设计的激光谐振腔,两端臂像散能够完全被补偿,实验上实现了基模高斯光束输出;当激光晶体热透镜焦距改变时,该方法所设计出的激光谐振腔内各关键位置光斑半径的变化,显著地小于普通谐振腔,在相同外界条件下,其输出激光功率稳定性明显优于普通激光器.     

Yb3+-doped 200 μm diameter core, gain guided index-antiguided fiber

The lasing in an end-pumped gain guided index-antiguided (GG-IAG) Yb³⁺-doped silicate glass fiber with a 200 μm diameter core is demonstrated. Laser beams with similar beam propagation factors M ² and mode field diameters W ₀ (>160 μm) were observed at the output end of the GG-IAG fibers under different pump powers, which indicated that single mode behavior and excellent beam quality were achieved during propagation. Furthermore, the laser amplifier characteristics in the present Yb³⁺-doped GG-IAG fiber were also evaluated.     

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.