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.     

全固体小型Yb:YAG激光器热效应及输出特性研究

利用中红外相机及干涉测量技术研究了二极管泵浦小型Yb:YAG激光增益介质在激光及非激光条件下的温度分布、温度梯度、热透镜效应,同时根据对热效应的研究,对激光器的参量进行了优化研究了在不同掺杂浓度下激光器的输出特性对于2.3at.%掺杂浓度,得到激光输出功率为1.7W,斜效率26.2%,光光转换效率为13.5%的实验结果;对于5.0at.%掺杂浓度,得到激光输出功率为2.5W,斜效率51%,光光转换效率为24%的实验结果。     

Temperature dependence of efficiency and thermal lensing of diode-laser-pumped Nd:YAG lasers

Efficiencies, lasing thresholds and thermal lensing of a Nd:YAG rod side-pumped with two 10 W diode-laser-arrays are measured for various rod temperatures between 80 K and 380 K. The threshold is reduced by a factor of 2.5–4 on cooling from room temperature to about 100 K, while the slope efficiency is increased by between 0% and 50% depending on the reflectivity of the outcoupling mirror. Extrapolation to a 240 W pumped laser gives an increase in optical efficiency of 25% to 30%. The thermal lensing measured with a beam deflection and an interferometric method is reduced by a factor of 10.     

Study on optical characteristics of Nd:YVO4/YVO4 composite crystal laser

Thermal effect in crystals is the main obstacle blocking diode-pumped solid state laser to get high and stable output power. Diffusion bonding crystal has been demonstrated to be an effective method to relieve the thermal lensing theoretically based on the numerical heat analysis to the end-pumped anisotropic laser crystal. The temperature distributions in Nd:YVO4/YVO4 composite crystal and conventional crystal were analyzed and compared. The end-pumped Nd:YVO4/YVO4 composite crystal laser was designed and set up with z-cavity. The maximum output powers of 9.87 W at 1064 nm and 6.14 W at 532 nm were obtained at the incident pump power of 16.5 W. The highest optical-optical conversion efficiencies were up to 59.8% at 1064 nm and 37.2% at 532 nm respectively.     

Nonlinear absorption and refraction effect on thermal lensing of solid-state laserrods

In this work, the effect of nonlinear absorption and refraction on thermal lensing of an end-pumped solid-state laser rod is investigated. At high input pump powers and on the focused region of thermal lensing, nonlinear responses of the active medium will be important. By considering the nonlinear absorption and refraction, the intensity distribution inside the rod is obtained. A convergence lens models the intensity dependency of the refractive index. By modeling of the laser rod with some contributed effective lenses, the stability condition of a typical laser resonator is investigated.     

Thermal lensing compensation principle for the ACIGA's High Optical Power Test Facility Test 1

Thermal lensing is becoming recognized as one of the dominant obstacles to the second generation of laser interferometric gravitational wave detectors. Very high optical power is required to circulate in the interferometer to reach the sensitivity goal, creating strong thermal induced wavefront distortion. These effects will be studied at the High Optical Power Test Facility in Gingin, Western Australia. In this paper, we present simulation results for the first test planned for the middle of 2004. This experiment will produce 5 kW of optical power circulating inside a Fabry–Perot cavity and will demonstrate large thermal lensing effects. Two compensation methods were investigated to offset the negative effect of thermal lensing on the cavity: a compensation plate within the arm cavity and adaptive laser mode matching. Advantages and disadvantages of both systems are discussed.     

强激光作用下非热平衡状态光学元件的热透镜效应

 研究了强激光作用下非热平衡状态光学元件的热透镜效应。对在强激光作用下的光学元件的透射激光方向角进行了时序观测。实验发现,光学元件在达到热平衡状态之前,其热透镜效应呈现某种波动起伏的特征。对这一现象提出了初步解释,并指出其实际意义。     

Transient temperature profile in the gain medium of CW- and end-pumped passively Q-switched microchip laser

The transient temperature profile in CW- and end-pumped passively Q-switched (PQS) microchip laser is investigated qualitatively by treating the population inversion (thereby the thermal load) as the sawtooth function of the time. The numerical results reveal not only the dynamics of thermal buildup, but also the dependence of the quasi-steady-state temperature rise and the repetitively oscillatory amplitude on the incident pump power and the pulse repetition rate of PQS laser. The abruptly ascending branch of the repetitive temperature oscillation is synchronized with the pulsing stage of PQS laser. As the result, the abrupt temperature transition during the pulsing stage would introduce the fluctuation into the PQS pulse parameters (pulse energy, pulse width, and peak power) via temperature-dependent stimulated emission and thermal lensing effect.     

激光窗口热透镜效应对光束质量的影响

 分析了高功率激光通过窗口时，引起的窗口热透镜效应及其对激光光束质量的影响。用冲量定理方法，推导了二维热传导方程的广义傅里叶级数解，然后按照平面热应力问题，运用有限元方法数值计算热变形。考虑热变形、折射率随温度变化，忽略光弹性效应，解出出光面的波前相差分布，讨论了远场光束质量。以空心环形光束为例，计算了熔融石英(SiO₂)和白宝石(Al₂O₃)两种常用窗口的温升分布、热变形、波前相差和光束质量，分析了冷却、辐照时间、光强分布的空间梯度和各种材料参数对光束质量的影响。     

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.     

A new technique for spatially resolved thermal lensing measurements

A new method is presented for spatially resolved thermal lensing measurements using multiple narrow probe beams and a two-dimensional array detector. The method is applied to an Er, Tm, Ho: YAG laser rod. No significant deviation from a parabolic temperature profile has been found although there is extraordinarily strong thermal lensing in the crystal. Thermo-optical constants of the material are reported.     

固体激光器热透镜效应的调控

利用工作腔的热透镜模型, 分析了有激光发射下固体激光器的谐振腔配置对热透镜效应和稳定区的影响, 论述了通过改变谐振腔配置调控热效应的可行性.实验上, 使用一台Nd: YAG激光器对理论作了验证, 实现了对热透镜光焦度及稳定区分布的调控.     

侧面抽运板状激光介质的热汇冷却

高热负荷固体激光介质的热效应已经成为制约激光器功率进一步提高的严重障碍,只有对激光介质进行有效的冷却才能保证其安全运行。以不均匀换热系数模型为基础,研究了具有非均匀内热源的侧面双向抽运板状激光介质在狭窄通道强制对流冷却情况下的耦合换热问题,对热汇冷却方案下介质的温度分布和热应力分布进行了数值模拟和分析,并对复合介质、蓝宝石和金刚石三种热汇材料进行对比。结果表明,忽视换热系数的非均匀性将导致应力计算结果偏低。对于侧面抽运、侧面冷却的激光介质,金刚石热汇冷却方案最佳,蓝宝石热汇方案次之,而复合介质方案不宜采用。     

端面抽运固体激光器热透镜效应的实验研究

提出一种易于实现、对激光器本身没有干扰、高空间精度、可实时测量介质热透镜的干涉测量方法. 并利用此方法全面研究了端面抽运Nd:YVO4激光器的热透镜效应，为认识激光介质的热效应和设计此类激光器提供了参考.  关键词： 热透镜 端面抽运 固体激光器     

Spectroscopic and laser properties of Nd~(3 ) ions in LaMgAl_(11)O_(19) crystals

The spectroscopic properties, optic quality and thermal lensing effect of Nd~(3 ) ions in LaMgAl_(11)O_(19)(LNA) crystals are investigated and the dependence of the laser characteristics on above properties are discussed.     

激光二极管端面纵向泵浦Nd:YVO_4激光器的热效应研究

针对激光二极管端面纵向泵浦Nd:YVO4激光器,本文理论和实验详细研究了Nd:YVO4晶体的热透镜效应。在激光二极管的中心波长分别为808nm和880nm及分别采用单端端面纵向泵浦和双端端面纵向泵浦结构情况下,实验测量了Nd:YVO4晶体的热透镜焦距,实验结果和理论预测基本吻合。同时在泵浦功率60W时获得了18.8W的连续基横模激光输出。     

切向气流和激光作用下碳纤维/环氧材料的损伤特性

无气流和切向气流马赫数分别为0.50,0.85条件下,开展了碳纤维/环氧材料激光辐照损伤特性研究实验,对碳纤维、环氧树脂和复合材料热失重曲线、温度历史曲线以及实验后复合材料损伤形进行分析,结果表明:由于切向气流阻止材料燃烧且对材料表面起冷却作用,无气流条件下材料的热损伤区域远大于激光辐照区域,与切向气流条件相比,材料后表面温升时间长、温升幅值高;在切向气流环境下,由于气流作用使得材料的损伤包括烧蚀损伤和断裂损伤;从损伤形貌和后表面温度历史、温升速率比较来看,在切向气流马赫数为0.50~0.85的速度范围内,碳纤维/环氧材料在切向气流和连续激光(102 W/cm2量级)联合作用下的损伤差异不明显。     

喷流冷却复合陶瓷薄片激光器的热特性仿真分析及实验研究

为分析喷流冷却复合陶瓷薄片激光器的热特性,设计用于冷却复合陶瓷薄片的喷流冷却系统.利用湍流换热理论和计算流体动力学仿真方法建立喷流冷却复合陶瓷薄片激光器的流固耦合热仿真模型,定义评价其冷却能力和冷却均匀性的定量参数.根据该仿真模型得到喷流冷却系统的最优设计参数,并进行实验验证.使用163孔喷板,流量为0.2kg/s,入口温度为20℃,在1200 W泵浦时获得359 W激光输出功率,并测得复合陶瓷薄片上表面的最高温度为92℃.激光输出功率与复合陶瓷薄片上表面温度均与泵浦功率呈近似正线性关系,且温度的实验值与仿真值相符度较高.     

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.