| 题名 | 高功率激光驱动器谐波转换与精密诊断测量研究 |
| 作者 | 季来林 |
| 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 | 林尊琪 |
| 关键词 | 惯性约束聚变 谐波转换 相位调制 啁啾脉冲 |
| 其他题名 | The study of harmonic generation and precision diagnostic techniques of high power laser driver |
| 中文摘要 | 随着ICF物理实验的深入，对驱动器输出提出了许多新的要求，如在高强度的主脉冲前沿有一个十几纳秒的比较低的台阶脉冲前沿，预、主脉冲强度比达到1：9以便实现靶向心压缩和中心点火，同时利用CPP和SSD技术进行焦斑形态控制，以抑制激光与等离子体相互作用中的各种不稳定性，要求光束具有~百μrad空间角谱宽度和0.3～0.5nm谱线宽度，这些特点对驱动器谐波转换设计提出了许多新的问题，如高的强度动态范围与谐波转换接收角宽和谱宽的平衡，谐波转换过程中的近、远场的光束质量控制，高强度三倍频光束传输的取样、诊断测量等。本论文基于高功率激光驱动器谐波转换物理模型和理论、数值模拟分析当前SGII装置中的谐波转换中光束传输变化，包括空间、时间相位调制对近、远场，谐波转换效率以及下游光学元件损伤影响等，完成SGII升级谐波转换与三倍频诊断成像系统设计，并解决了许多与之相关的工程问题，在学习期间主要完成以下几方面工作： 1.根据神光II升级的激光驱动器输出特性，充分考虑基频泵浦强度动态范围与接收角宽和带宽的平衡，优化设计了两组谐波转换方案，在小焦斑打靶情况下采用14mm Type I KDP SHG (detuned 180μrad)/11mm Type II KDP THG, 该方案具有较大的动态范围和高的转换效率，2010年的实验中转换效率达到~70%@ω &2500J&2ns，在终端集成实验中实现到靶效率~55% @ω&4000J &3ns；针对大焦斑打靶的需求，设计采用12.5mm Type I KDP SHG (detuned 170μrad) /11mm Type II KDP THG方案，该设计角度容差超过100μrad，能够很好满足升级物理实验需求，但动态范围较小； 2.在神光II第九路上，完成三倍频的近、远场初步测量诊断，通过对近、远场测量结果分析，国内第一次发现三倍频光束存在明显的中频周期调制，调制周期~12mm，理论分析其对DPP匀滑远场具有明显的影响，这将会导致靶面产生幅度为10%-15%大尺度的强度调制，这与物理实验结果基本相符，该工作可用于指导国内晶体加工质量改进，在减小PSD1的RMS基础上，还必须进一步消除具有良好周期性的调制；并根据谐波转换与光束传输理论进一步分析晶体加工对终端组件的下游光学元件的自聚焦破坏威胁，分析结果表明SGII升级终端光学元件B积分特征值IL应该控制在15GW/cm左右； 3.基于升级三倍频诊断测量基本物理需求分析，利用ZEMAX程序设计三倍频测量成像系统，该系统采用三面大口径球面镜组成离轴无焦望远卡塞格林系统，远场成像视场可达5mm×5mm，近场空间分辨率可达500μm，该设计巧妙地利用反射成像系统进行高通量光束衰减取样，同时回避了大口径非球面镜加工制造，降低光学加工难度，目前该设计已用于SGII升级系统； 4.设计了三倍频模拟光源，利用单透镜实现光纤与空间滤波器的F数匹配耦合，减少传输损耗，该光源空间结构紧凑，性能稳定，已用于工程项目； 5.针对SGII升级第九路啁啾脉冲输出特点（Δλ~3.5nm，τ~1.5ns ），设计II类晶体正交级联倍频方案，该方案利用两块晶体轻微小角度相反方向失配，补偿啁啾脉冲因带宽引起相位失配，理论研究表明其高效转换带宽可以达到~10nm，在九路装置上可实现千焦耳的啁啾脉冲倍频输出。 |
| 英文摘要 | With the development of ICF , there are many new challgences were proposed for the high power laser driver. Such as, the main pulse should be with a dozen nanoseconds low intensity prepulse, the prepulse to main pulse ration is near 1:9 ; the CPP and SSD was used to smooth the focal spot to suppress the Laser plasma instablity, which require the beam with ~100μrad divergence and 0.3~0.5nm bandwidth. These cause many new problems for the harmonic generation design in high power laser driver, such as the balance bettwen intensity dynamic range and the acceptance anguar, the beam quaility control of the near/far field, the sampleing and diagnotic of high fluence 3ω laser. The harmonic gengeration process on SG II has been studied with the numerical simulation based on the theoretic modle, inculding the spatial、temporal modulation、wavefront distort, the relation bettwen near/far field with this modulation and the optics damge in the downstream have been detailed discussed in article. We also designed the third harmonic generation systems and an image system for the precision diagnostic of the third harmonic for the SG-II upgrade project in this paper. The main progress is as following: 1.According to the characteristic of SG II upgrade, two sechems of third harmonics were designd for the SGII upgrade project, 14mm Type I KDP SHG (detuned 185μrad)/11mm Type II KDP THG was designed for small focus spot, which has a large dynamic range and high conversion efficiency for small focus spot, it has been used in the experiment at 2010, and the conversion efficiency reached ~70% @ω&2500J&2ns on SGII NO.9 facility, the efficiency for the energy delivering on the target reached ~55% @ω & 4000J & 3ns with the final optics assemblies. But taking into account the beam smooth requirements ~ 100μrad beam divergence tolerance, 12.5mm Type I KDP SHG (Detuned 170μrad) / 11mm Type II KDP THG design was chose, its acceptance angle can be up to 100μrad with low intensities dynamic range; 2.The preliminary diagnosis of 3ω near/far field was accomplished on the SGII NO.9. There was a periodal intensity modulation in the 3ω beam, the period~12mm, it has a significant impacts on the far fied, and lead to 10% -15% of the large-scale intensity modulation in smoothing spot with DPP, which is in agreement with the results of physical experiments, it can be used to improve the domestic crystal fabrication, According to analysis of the threat of self-focusing in downstream optics caused by the modulation with the crystals’ ripples, IL, the eigenvalues of B integral, should be controlled at about 15GW/cm in SGII upgrad project; 3.According to the requirements of 3ω diagnostic system, the imaging system for precision diagnostic was designed with ZEMAX. This system employs three spherical mirrors which composed the off-axis Cassegrain telescope system, the view field for focal spot overs 5mm×5mm, and the spatial resolution of near field is up to 500μm, this design is clever use of reflective imaging system for attenuation sampling, while avoiding fabrication of large aparture aspherical lens, it has been used in the SGII upgrade; 4.A compact and stable 3ω simulation source was designed for the SGII upgrade project, which contains a fiber and single lens. The output NA of this system matched with transport filter lens, so the loss has been significant reduced and it has been used in the project. 5.A second harmonic generation (SHG) system with two Type II KDP crystals in quadrature was proposed for the chirp pulse（Δλ~3.5nm，τ~1.5ns ） of SGII NO.9. The acceptance bandwidth of this scheme is close to 10nm by using two crystals with slightly different angular detuning from phase matching, the second harmonic energy is up to 1000J with the conversion efficiency of 55% for the chirp pulse on SGII NO.9. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15875]  |
| 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 | 季来林. 高功率激光驱动器谐波转换与精密诊断测量研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
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