【作者】 曹丁象；

【导师】 谭吉春； 郑万国；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2008， 博士

【摘要】 由于聚变能工程（IFE）固体激光驱动器、定向能武器（DEW）等领域的需求牵引,高功率、大能量的二极管泵浦固体激光器（DPSSL）已经成为国内外的研究热点。待解决的关键问题,是如何有效地提高激光器的输出功率和改善光束质量。提高输出功率和改善激光光束质量面临的最主要障碍是激光系统的热效应。本文深入地研究了重频、大能量激光器件的热管理技术,主要内容包括四个部分:1、重频、大能量二极管泵浦Yb:YAG激光系统的物理设计及热管理技术;2、设计、研制两种高平均功率普克尔盒:热补偿和重频等离子体普克尔盒;3、热容模式下固体激光器的热效应理论研究和输出特性的实验研究;4、大口径钕玻璃片状放大器的动态热畸变及热恢复研究。一、重复频率、大能量Yb:YAG激光系统的物理设计和热管理技术研究进行了准三能级激光振荡器的物理设计。建立了调Q激光脉冲的时-空演化动力学模型,获得了激光光束质量随时间的演变过程的仿真结果。考虑增益介质的受激吸收和发射截面的谱分布,建立了时间—光谱分辨的准三能级激光振荡模型,研究了Yb:YAG增益开关激光器的波长竞争问题。研究了基于准三能级Yb离子的脉冲储能型放大器的设计和参数优化问题,在考虑自发辐射放大（ASE）退泵浦效应和狭窄通道内流体的强迫对流换热性能等因素的条件下,研究了基于准三能级Yb离子的脉冲储能型DPSSL的设计和参数优化问题。在国内首次给出了10Hz、100J级的Yb:YAG放大器增益介质的一组优化设计参数:泵浦强度22kW/cm²,介质口径10cm²,厚度0.55cm、掺杂3.92×10²⁰cm^-3。以上两项研究结果为本文设计100J级激光系统及优化热控制方案奠定了理论基础。高效的热管理是准三能级激光器实现重频、大能量输出和改善光束质量的一项关键技术。本文以耦合换热物理模型为基础,完成了重复频率大能量DPSSL水冷系统的建模以及温度场、流场的仿真分析。在此基础上设计了用于V形主动镜构型Yb:YAG激光头的水冷系统;针对高强度泵浦的10Hz、100J级Yb:YAG片状放大器,提出了“热平衡”的双面冷却方案。建立了热沉和增益介质的接触热分析有限元模型,完成了10Hz、100J级Yb:YAG放大器在液氮温度下基于宝石热沉的端面传导冷却设计。开展了平凹腔和超高斯反射镜腔Yb:YAG激光振荡器的实验研究,测量了不同温度下的激光输出能量。二、两种高平均功率普克尔盒的设计与研制数值模拟了KDP、DKDP、BBO等几种非线性光学晶体在高平均功率载荷下的热-力学特性以及热畸变。测量了DKDP晶体在平均功率激光辐照下的温度分布。设计并研制了大口径DKDP热补偿普克尔盒,定量分析了晶体厚度误差、光轴偏差以及两块晶体的温度差异等因素对普克尔盒性能的影响。进行了热补偿效果的实验验证。优化设计并研制了重复频率等离子体普克尔盒。通过数值模拟,完成了重频等离子体普克尔盒的端面传导冷却设计。三、热容模式下Nd激光介质的热-力分布特点和激光输出特性研究首先针对热容工作模式下激光介质内废热持续积累的特点,从激光介质的实际增益分布得到内热源载荷条件,建立了非稳态热-力学仿真模型,在此基础上开展了激光介质工作条件的热.力学优化研究;建立了热容模式下的光传输理论模型,分析了激光介质动态热畸变,指出了因泵浦光未能完全充满介质端面,从而引起的端面不均匀形变是造成光学畸变的主要原因。研制了1kW级氙灯泵浦的V形有源镜构型Nd:YAG热容激光器,实验验证了此构型热容激光器具有定标放大能力。四、400mm×400mm口径钕玻璃片状放大器的泵浦致波前畸变和泵浦致热退偏以及热恢复过程研究分别讨论了钕玻璃片的温度梯度和热变形对激光波前畸变的贡献;为了缩短××激光装置的运行周期,优化设计了冷却方案。论文在以下四方面取得了有创新意义的研究结果:1、准三能级激光振荡器的设计和光束质量控制将激光速率方程理论和光波的角谱传播理论有机结合起来,对谐振腔内光脉冲的形成、传播过程建模,研究了超高斯镜非稳腔调Q激光脉冲时—空瞬态特性,获得了激光光束质量随时间的演变过程的仿真结果。考虑增益介质的受激吸收和发射截面的谱分布,建立了时间—光谱分辨的准三能级激光振荡模型,研究了Yb:YAG增益开关激光器的波长竞争问题。上述两项研究对优化准三能级激光振荡器的设计和光束质量控制具有重要指导作用。该研究结果迄今未见国内有相关报道。2、10Hz、100J级“水冷型”和“端面传导冷却型”片状放大器针对高强度泵浦的10Hz,100J级Yb:YAG放大器,提出了“热平衡”双面冷却方案:在高的热负载区使用强的水冷,在低的热负载区使用弱的He气流冷却。在国内首次实现了宝石端面传导冷却型10Hz、100J级Yb:YAG放大器热沉结构的优化设计;并定量评估了宝石-Yb:YAG用液氮端面传导冷却和直接水冷两种方案的冷却效果。该研究结果迄今未见国内有相关报道。3、高平均功率“热补偿普克尔盒”和“重复频率等离子体普克尔盒”在国内首次分析了热补偿普克尔盒的加工误差和晶体温度差等因素对其性能的影响,完成了大口径（64mm×35mm）DKDP热补偿普克尔盒的设计;创新地提出了单脉冲驱动DKDP电容分压法,实现了重频等离子体普克尔盒在半波电压点的稳定可靠运行。4、热容激光器研制了V形有源镜构型片状热容激光器,完成了集成演示实验,获得约47J/脉冲（20Hz,1kW级）的输出能量;斜效率达到1.3%,系统总效率达1.2%,实验结果表明:激光输出能量与模块数目基本呈线性关系,从而证明该多模块构型的有源镜激光器适合于高平均功率运行。分别对平凹稳腔和角锥棱镜腔进行了光束质量研究,在使用角锥阵列腔时,远场光束质量约为10倍衍射极限。更多还原

【Abstract】 With the increase of the demands of inertial fusion driver and military weapon, high power & large energy diode-pumped solid-state laser(DPSSL) has become one of the main objectives of current research and development activities within the laser community.DPSSL has become one of the most promising approaches in the high-power laser engineering.Research of DPSSL has mainly concentrated on scaling of output power,while remaining of a high spatial beam quality.The main problem hindering scaling of diode-pumped solid-state lasers is heat deposition within the laser medium.A detailed investigation of the theoretical design and thermal aspect for the high average power and large energy DPSSL and the thermal management technology is reported in this dissertation,including four parts contents.The first part is theoretical design and thermal management for the pulsed energy-storage quasi-three-level Yb-ion DPSSL.We begin with the discussion on the quasi-three-level laser oscillator performance model,which predicts both intensity and spectrum evolutions of the laser output.Followed by the numerical simulation of the spatio-temporal dynamics of the pulse formation in the diode-pumped Q-switched Yb:YAG laser.We then study in details the optimal design for the pulsed energy-storage Yb:YAG amplifiers considering the criteria of amplified spontaneous emission(ASE) and the capability of forced convection cooling in a narrow passage.Finally,based on our model,the baseline parameters are presented for a 100J-class diode-pumped Yb:YAG disk amplifiers.Efficient thermal management is the key technology for average power Yb lasers. The thesis investigates the temperature distributions and liquid flow of the cooling system utilizing the concept of forced convection to cool the Yb:YAG disk laser.The numerical simulation platform was built based on coupling thermal exchange model and turbulent flow model.Based on this numerical platform,the water cooling system is presented for V-shape Yb:YAG laser.Finally,the numerical calculation model of thermal contact was built and the simulation was carried out by ANSYS finite element program.Then the Sapphire cooling at both faces of high-power cryogenic Yb:YAG disk laser is optimized according to the model.The second part is about thermal aspect and design for the high average power Pockels cell.Firstly,the numerical calculation model for thermo-mechanicss of nonlinear crystals such as KDP,DKDP and BBO which used in high average power laser systems was built and the simulation was carried out by ANSYS finite element program.We then investigate in detail the machining or assembly errors and performance of a thermal compensation pockels cell(TCPE).Based on these analyses, the large aperture TCPE based on DKDP has been developed successfully.Finally,we discuss the theoretical design of repetitively plasma-electrodee pockels cell,then we have completed thermal modeling of a scaleable,face-cooled repetitively plasma-electrodee pockels cell.The third part is for thermal effects and laser characteristics of solid state heat capacity lasers(SSHCL).An unsteady-state thermomechanics model was established in the condition of the practical distribution of gain in the laser medium according to the characteristics of waste heat accumulate persistent in laser medium when working on the mode of heat capacity.Based on this model the thermomechanics optimization was done. Furthermore a theoretical model of the optical transmission was established to study the optical distortions which result from the dynamic thermal effect.The numerical simulation research shows that the main optical distortion is result from the bulging of the end face because it is not pumped fully aperture.The research also included lots of experimental study.A new type of a high-efficiency V-shape active-mirror laser was proposed,which was composed of four modules with two large-aperture Nd:YAG slabs in each module.The experiments verifies that the output energy has a linear scaling law with the module number,which implies that this kind of multi-module large-aperture active-mirror laser would be suitable for high-average-power laser operation.The final part is the investigation of pump-induced wavefront distortion and the thermal recovery of the large aperture Nd:glass amplifiers.The main innovation points are summarized as following:1.Quasi-three-level laser oscillator performance modelThe model to describe the spatio-temporal dynamics of the pulse formation in the diode-pumped Q-switched Yb:YAG laser is established.This model,based on the rate equations of quasi-three-level and the theory of scalar diffraction,predicts the value of the beam-quality factor M~2 during the pulse evolution.The model to describe the spectral dynamic behavior of quasi-three-level laser resonators operated in gain-switched conditions is also established.Numerical simulations of our analytical model are useful to optimal design quasi-three-level laser resonators.2.Water cooled & conduct cooled Yb:YAG disk for the 10Hz,100J-class amplifierThe feasibility of cooling 10Hz/100J amplifier with "thermal equilibrium" cooling configuration have been demonstrated:Back pumping and bank cooling with water while the front face is cooled by air.The numerical calculation model of thermal contact was built and the simulation was carried out by ANSYS finite element program.Then the Sapphire cooling at both faces of cryogenic Yb:YAG disk for the 10Hz,100J-class amplifier is optimized according to the model.We compare the peak temperature of Yb:YAG for water cooled and conduct cooled scheme.The results show that temperature rise achievable with conduct cooled is quite low to those obtained with water cooled.3.Thermal compensation Pockels cell and rep-frequency plasma-electrodee Pockels cell for high average powerWe study in details the machining or assembly errors and the performance of thermal compensation pockels cell(TCPE) for the first time.Based on these basic analysis,the large aperture(64mm×35mm) TCPE based on DKDP has been developed successfully.Experiments have validated the feasibility of TCPE for high average power applications.The optimal design of rep-frequency plasma-electrodee pockels cell were proposed and realized for the first time.By optimizing the configuration of the Pockels cell,the DKDP Pockels cell can be operated only by switching pulse thanks to the share voltage capacitance added.4.A new type of a high-efficiency V-shape active-mirror laser was proposed, which was composed of four modules with two large-aperture Nd:YAG slabs in each module.The experimental results show that the maximum output energy is about 47J with an overall efficiency of 1.2%and slope efficiency of 1.3%.Also,the experiments verifies that the output energy has a linear scaling law with the module number,which implies that this kind of multi-module large-aperture active-mirror laser would be suitable for high-average-power laser operation.The experiments of the retro-reflector array to improve the quality of SSHCL were carried out in this paper.The experiment results show that the action of retro-reflector array to reduce beam’s focal spot size was testified visibly and≤10TDL spatial beam quality can be reached.更多还原