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chi20180620上海光机所李学春557443The high-power front-end pre-amplification system needs to provide the main amplifier of the ICF system with nanosecond laser pulses of specific time waveforms, Joule-level energy, and square-type laser spots. To meet the high repeat frequency requirements of the driver, the pre-amplification system needs to be stable in output energy and of high quality for high energy pulses. The main issues that need to be addressed include the design of new laser heads for higher-frequency and higher-energy laser heads, efficient and stable thermal management solutions, multi-pass amplification technologies for large energy output, and compensation technologies for system thermal effects, etc. The dissertation mainly focuses on the above-mentioned technologies and the main research direction is air-cooled or solid-cooled Nd:glass multi-slab amplifiers. To increase the repetition frequency of the front-end pre-amplification system, reduce the thermal effect of the pre-amplification system, and improve the system’s conversion efficiency, the laser diode pumped solid-state laser (DPSSL) shows great potential and advantages. In this paper, based on the air-cooled multi-slab amplification system widely used in the world, the thermal effects and gain property of the air-cooled chip amplifier are studied. For the first time, a sapphire-cooled Nd:glass slab amplifier is proposed. The main research content is as follows: 1. A numerical simulation model of a pre-amplification system was established, including the beam tracing model of the pump system, the heat distribution model inside the laser medium, the numerical model of the fluid thermodynamics, the numerical model of laser induced wavefront distortion and depolarization, and the energy storage conversion model of the medium, the ASE induced energy loss model and the multi-pass amplification model. These models are used to numerically simulate the spatial distribution of the output beam of the pump-coupled system, the distributions of the temperature, thermal stress and thermal deformation within the laser medium, the velocity and temperature distribution of the liquid flow between the laser slabs, thermally induced wavefront distortion and depolarization loss within the heated gain media slab, the energy flow distribution of the amplification system, and the pulse amplification in multi-pass amplifiers, etc. Based on experimental data of the helium cooling Nd:glass slab amplifier system and the sapphire cooling Nd:glass slab amplifier system, the theoretical and numerical models are checked and improved. Using the established numerical models, the output states of the slab amplifier system under different conditions were simulated, providing the basis for the desingning and improvement of the amplifier. 2. For the problem of fluid turbulence affecting the quality of the laser beam in the fluid-cooled slab amplifier structure, a sapphire-cooled Nd:glass structure was proposed. The optical bonding process between solid plates was explored. Using the principle of liquid capillary bonding, the optical bonding with a 3 cm contact aperture between sapphire and Nd:glass was achieved. The experimental results show that the success rate of optical bonding depends mainly on the surface quality of the plates where the fluctuation of the surface should be<0.2λ. Three kinds of thermal management schemes for the optical bonding assembly were explored experimentally, namely the Indium film conduction scheme, the liquid metal conduction scheme, and the cooling water conduction scheme. Under 15 kW/1 Hz pump conditions, thermally induced wavefront distortions in the three schemes were investigated. The PV values are 0.35λ, 0.185λ, and 0.147λ, respectively. 3. A sapphire-cooled Nd:glass slab laser head has developed. The laser head uses four groups of sapphire and Nd:glass optical bonding components. Gradient doping technology is used to achieve uniform energy storage and gain. The laser head uses cooling water to directly cool the optical bonding assembly. Under the pump condition of 40 kW/1 Hz, a single-pass small-signal gain of 1.8 was obtained, and the single-pass transmitted wavefront distortion of the laser head was 0.21 λ. Based on the sapphire-cooled Nd:glass slab laser head, a multi-pass amplification system was built. The system achieved a pulse energy output of 560 mJ and a power stability of 0.39% RMS under 20-pass amplification. The near field modulation is 1.33, and the far field spot corresponds to 1.6 and 1.7 times the diffraction limit on the x and y axes, respectively. 4. The theoretical model of the Helium gas cooling Nd:glass amplifier was perfected. The thermal-induced wavefront distortion of the Helium gas was considered. The total thermally induced wavefront distortion PV value of the theoretical simulation was 0.18 λ, which was basically the same as the experimental measurement value of 0.21 λ. Anastomosis. The ability of the deformable mirror to compensate for the wavefront distortion of the sheet-shaped gain medium was experimentally studied. Using a 16-channel deformable mirror with a diameter of 20 mm, the wavefront with a PV value of 4.2 λ can be compensated to 1.45 λ. Theoretically and experimentally, the gain properties of the multi-chip glass-manufacturer are studied. It is proposed to increase the small-signal gain of multi-slab amplifiers by increasing the columnar doping density. 5. The numerical simulation theory of pulse compression and broadening using gratings and optical parametric amplification was constructed. The key parameters of the operating point and components were determined for the ps pulse amplification system; based on this, the picosecond OPCPA system with high stability and high contrast was improved. 300μJ ps pulse output can be obtained and the energy stability is 1.35% RMS. Time contrast after compressing is 414 fs, close to the diffraction limit; a pulse width measuring device is built and chceked with a commercial laser so that the pulse width of a ps or fs pulse at a repetition rate ≥ 1 Hz can be measured with this measuring device.2019atalunwen219115163253814solid cooling; slab amplifier; Nd:glass; liquid cooling; thermal effects; LD pumpedResearch on technologies of repetition-rate Joule-level solid state amplifier重复频率焦耳级固体放大器技术研究高功率前端预放大系统需要为驱动器系统的主放大器提供特定时间波形、焦耳级能量、方型光斑的纳秒激光脉冲,为了迎合驱动器未来高重复频率的要求,使预放大系统输出稳定、高质量的大能量脉冲,需要解决的主要问题包括面向更高重频更高能量的新型激光头结构设计,高效稳定的热管理方案、面向大能量输出的多程放大技术和系统热致效应的补偿技术等。论文主要针对以上提及的技术进行研究,主要研究方向为气冷或固体冷却的多片式钕玻璃放大器。 为提高前端预放大系统的重复频率,减小预放大系统的热效应,提高系统转换效率,激光二极管泵浦的固体激光器(DPSSL)显示了巨大的潜力与优势。本论文结合世界范围内广泛应用的气冷多片式放大系统,研究了气冷片状放大器的热效应与增益特性,首次提出了蓝宝石冷却钕玻璃片状放大器。主要研究内容如下: 1.建立了预放大系统的数值模拟模型,包括泵浦系统的光束追迹模型、激光介质内部的热分布模型、流体热动力学数值模型、激光热致波前畸变与退偏数值模型、增益介质内部储能转化模型、ASE对储能消耗模型和激光多程放大模型等。利用这些模型,数值模拟了泵浦耦合系统输出光束的空间分布形态、激光介质内部的温度、热应力和热变形分布、片状介质间的气流流速与温度分布状态、片状增益介质内的热致波前畸变与退偏损耗、放大系统的总体能流分布和多程放大脉冲能量变化等,并根据氦气冷却钕玻璃片状放大器系统与蓝宝石冷却钕玻璃片状放大器系统的实验数据,校核了理论数值模型。利用建立的系统数值模型,模拟了不同条件下片状放大系统的输出状态,为放大器的改进工作提供了依据。 2.针对流体冷却片状放大器结构中流体湍流对于激光光束质量产生影响的问题,提出了蓝宝石冷却钕玻璃结构。探索了固体片之间的光胶工艺,利用液体毛细键合原理,实现了3 cm接触口径的蓝宝石与钕玻璃片间光胶,实验结果表明,光胶作用的成功率主要取决于片表面面型,表面面型需求为<0.2λ。实验上探索了光胶件的三种热管理方案,即铟膜传导方案、液态金属传导方案和冷却水传导方案,在15 kW/1 Hz泵浦条件下,三种方案中热致波前畸变PV值分别为0.35λ、0.185λ和0.147λ。 3.研制了蓝宝石冷却片状钕玻璃激光头,激光头采用了四组蓝宝石与钕玻璃光胶组件,采用梯度掺杂技术实现储能与增益均匀化,激光头采用了冷却水直接冷却光胶件方案,在40 kW/1 Hz的泵浦条件下,获得了1.8的单程小信号增益,激光头单程透射波前畸变PV值为0.21λ。基于蓝宝石冷却片状钕玻璃激光头,搭建了蓝宝石冷却片状钕玻璃多程放大系统,系统在20程放大的条件下,实现了560 mJ的脉冲能量输出,能量稳定性达到了0.39% RMS,近场调制度为1.33,远场光斑在x、y轴分别对应1.6和1.7倍衍射极限。 4.完善了氦气冷却钕玻璃片状放大器的理论模型,考虑了氦气流体的热致波前畸变,理论模拟的总热致波前畸变PV值为0.18λ,与实验测量值0.21λ基本吻合。实验上研究了变形镜对于片状增益介质的波前畸变的补偿能力,利用口径为20 mm的16通道变形镜,可以将波前畸变PV值为4.2λ的波前补偿为1.45λ。在理论和实验上研究了多片式钕玻璃放大器的增益特性,提出了采用增加浓度厚度积的方式提高多片放大器的小信号增益。 5.构建了利用光栅实现脉冲压缩与展宽和光参量放大的数值模拟理论,为ps脉冲放大系统确定了工作点与元件关键参数;基于此改进了具有高稳定、高对比度的皮秒OPCPA系统,系统可以输出300 μJ的ps脉冲,能量稳定性为1.35% RMS,时间对比度高达10-8,压缩后的脉冲时间宽度为414 fs,接近衍射极限;搭建了短脉冲脉冲宽度测量装置,并与商用激光器输出进行了校核,利用此测量装置可以测量≥1 Hz重复频率下ps或fs脉冲的脉冲宽度。固体冷却;片状放大器;钕玻璃;流体冷却;热效应;LD泵浦中国科学院上海光学精密机械研究所黄庭瑞光学工程博士
中文题目: 重复频率焦耳级固体放大器技术研究
外文题目: Research on technologies of repetition-rate Joule-level solid state amplifier
作者: 黄庭瑞
导师姓名: 李学春
学位授予机构: 中国科学院上海光学精密机械研究所
答辩时间: 20180620
中文关键词:
固体冷却;片状放大器;钕玻璃;流体冷却;热效应;LD泵浦
英文关键词:
solid cooling; slab amplifier; Nd:glass; liquid cooling; thermal effects; LD pumped
中文摘要:
英文摘要:
文献类型:学位论文
学位级别: 博士
正文语种: chi
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