| 题名 | 重复频率固体激光放大器技术研究 |
| 作者 | 黄文发 |
| 学位类别 | 博士 |
| 答辩日期 | 2014 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李学春 |
| 关键词 | LD泵浦 重复频率 热效应 Yb:YAG 气冷放大器 SBS |
| 其他题名 | Research on Solid State Laser Amplifier Operating at Repetition Rate |
| 中文摘要 | 高重复频率、高效率、高功率是对惯性聚变能源激光驱动器的基本要求。激光二极管泵浦的固体激光器（DPSSL）因其转换效率高、输出能量大、光束质量好、结构紧凑、可以重复频率运行而成为实现惯性聚变能源的重要技术途径。但是，在固体激光放大器中，激光材料由于吸收了非均匀泵浦以及表面冷却会在其内部形成热梯度，重复频率运行更会造成热梯度的累积效应，一方面会引起光学畸变导致光束质量下降，另一方面会限制输出激光能量和重复频率的提高。因此选择合适的激光材料，采用高效的热管理技术对重复频率固体激光放大器的设计有着至关重要的意义。 本论文围绕重复频率激光二极管泵浦固体激光放大器中存在的热问题，以提高激光放大器的输出功率和转换效率为目的，开展对新型激光材料和热管理技术的理论和实验研究，主要做了以下几个方面的工作： 1. 研制了高稳定性重复频率低温Yb:YAG再生放大器的实验样机，并对系统的整体性能进行优化研究。首先研究了Yb:YAG晶体特性尤其是Yb:YAG晶体在低温下所表现出来优异光学性能。其次建立了重复频率低温Yb:YAG再生放大器的三维热分析模型，得到Yb:YAG温度场分布及由于温度梯度产生的应力应变分布，并详细分析了热效应对低温Yb:YAG再生放大器的影响。最后，为了给低温重复频率MOPA装置提供优质、稳定的种子脉冲，对低温Yb:YAG再生放大器进行了实验研究，得到优化的实验结果：在晶体温度为163 K，泵浦脉宽为1.8 ms，频率10Hz的工作状态时，在注入脉冲为120pJ、10ns的情况下， LD泵浦能量为185.4mJ时，再生放大器输出能量为11.3mJ，总增益超过107，光-光效率为6%，输出稳定性为±1.8%，光束质量因子M2<1.2，方波扭曲度SPD值为1.35，满足设计指标的要求。 2. 设计了重频LD泵浦气冷叠片放大器，并进行热验证实验研究。首先分析了气冷叠片放大器的结构和工作过程，并对气冷叠片放大器的主要结构单元进行了设计，包括气冷放大器激光头、LD泵浦源及泵浦光耦合传输系统以及气体循环系统，建立了LD泵浦气冷钕玻璃叠片放大器的热分析模型，利用Comsol Multiphysics软件对气冷放大器进行流-固耦合传热分析，得到气冷放大器的气流分布情况，以及钕玻璃片的温度分布和热应力分布。同时，计算了由热光效应、弹光效应以及端面形变引起的热致双折射和波前畸变，并提出了热致退偏和波前畸变的补偿方法。最后，在理论研究和主要结构单元设计的基础上，设计了焦耳级多程气冷钕玻璃放大器激光系统，讨论了两种技术路线的可行性，并详细分析了激光系统中的关键技术单元。另外，研究了一种“三明治”结构端面传导冷却方式，对不同的透明热沉材料进行了分析，并建立了蓝宝石端面冷却钕玻璃放大器的热分析模型，得到钕玻璃的表面温度分布和接触面内的热应力分布，同时也分析了接触面内的接触热阻对散热性能的影响。“三明治”结构端面传导冷却方式能明显减少增益介质的热沉积，增益介质的温升小，而且结构更简单紧凑，散热性能好，能满足激光放大器在重复频率下运行的需求，但是，“三明治”结构端面传导冷却方式对热沉材料的热力学参数要求很高，接触热阻对热沉材料的散热性能有较大的影响。 3. 在113K~293K的温度范围内，研究了单模光纤中受激布里渊散射特性。测量了不同温度下单模石英光纤受激布里渊散射的阈值、布里渊频移，并得到以下结论：对于后向斯托克斯光，温度越低其阈值越高；随着温度的升高，布里渊频移增大，在一定范围内布里渊频移与温度呈线性关系。温度对单模光纤中布里渊频移的影响较小，但受激布里渊散射阈值受温度影响则较为明显，因此在高功率光纤放大器中，可以利用对光纤进行温度控制来抑制光纤中的受激布里渊散射，从而提高放大器阈值输出功率，突破光纤放大器向高功率发展的关键技术瓶颈，具有一定的意义。 |
| 英文摘要 | “High repetition rate, High efficiency, High power” are three basic requirements for inertial fusion energy laser driver. Laser Diode-pumped Solid State Laser (DPSSL) has become an important technical way to achieve the goal of Inertial Fusion Energy (IFE) because of its several advantages: high conversion efficiency, high output energy, good beam quality, compact structure, repetition rate operation. However, due to absorption of non-uniform pump light and surface cooling, thermal gradient will be formed inside the laser medium in solid state laser amplifier, and will accumulate when repetition rate operation.Thermal gradient can cause two undesirable results: beam quality degradation and output energy as well as repetition rate is limited. So choosing the right laser material and efficient thermal management technologies for solid state laser amplifier operating at repetition rate is of great significance. In this dissertation, according to the thermal issues in the rep-rate LD pumped laser amplifier, with the purpose to increase the output energy and conversion efficiency, novel laser material and thermal management technologies are investigated in the following aspects: 1. We develop a highly stable diode-pumped cryogenic-cooled Yb:YAG regenerative amplifier and optimize the performance of the system. Firstly, We study the properties of Yb:YAG crystal discuss the characteristics of Yb:YAG crystal under cryogenic cooling conditions. Secondly, we develop a diode-pumped cryogenic-cooled nanosecond Yb:YAG disk regenerative amplifier used in a joule-class MOPA (master oscillator power amplifier) laser system and establish a 3-dimension finite element model to simulated the thermal, mechanical distribution in the Yb:YAG crystal, and analys the thermal effects impact on the diode-pumped cryogenic-cooled Yb:YAG regenerative amplifier. Thirdly, in order to provide a stable seed pulse for the rep-rate MOPA system, more than 11 mJ output energy of the Yb:YAG regenerative amplifier is obtained at 10 Hz repetition rate at 163 K with 1.8% energy fluctuations and excellent beam quality (M2 < 1:2), the optical to optical conversion efficiency is 6% with an overall gain exceeding 107, square pulse distortion (SPD) of 1.35 has been measured at the maximum output energy and the pulse duration decreases to 7.5 ns from 10 ns. 2. We design a LD pumped gas cooled slab laser amplifier. Firstly, we analysis the structure and operating principle of gas cooled slab laser amplifier, and also design the major architectural elements including amplifier head, pump delivery system and gas circulation system. Secondly, establishing the fluid-solid coupling theoretical model, we use Comsol multiphysics to compute the fluid distribution, resulting temperature and stress distribution of the nd:glass. Secondly, we study the thermal birefringence and wavefront distortion in the gas cooled nd:glass laser amplifier, induced by thermo-optic effect, elastic-optic effect and end deformation, meanwhile, we also propose methods to compensate thermal birefringence and wavefront distortion in the gas cooled laser amplifier. More over, we design a 2J/10Hz LD dual end pumped multi-pass helium gas cooled nd:glass laser amplifier system and detailed analysis of the key unit technologies of the laser system. Finally, we study “sandwich” end face conduction cooling. Different transparent heat sink materials and a sapphire end face conduction cooling nd:glass amplifier have been investigated. We establish the thermal finite element model to compute the temperature and stress distribution in the “sandwich” and analys the contact resistance in the face between sapphire and nd:glass. “sandwich” end face conduction cooling can significantly reduce the heat deposition in the laser medium with compact structure and good heat dissipation performance, meeting the needs of the laser amplifier operating at repetition rate. However, two major challenges of the “sandwich” end face conduction cooling are suitable heat sink materials and contact resistance. 3. Stimulated brillouin scattering (SBS) threshold and frequency shift of single mode fiber is studied under the temperatures from 113K to 293K. Basing on the theory of SBS，the relation of SBS threshold and frequency shift with temperature is analyzed. Experiment system is designed and built，brillouin frequency shift and threshold of 2 km single mode fiber are measured under different temperature. The experiments indicate that the lower temperature, the higher SBS threshold，low temperature can suppress stokes lights, the brillouin frequency shift increases linearly with the increasing the temperature. Temperature has a direct effect on the SBS of fiber. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15893]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 黄文发. 重复频率固体激光放大器技术研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
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