| 题名 | 高能拍瓦激光展宽系统及其相关技术的研究 |
| 作者 | 杨庆伟 |
| 学位类别 | 博士 |
| 答辩日期 | 2009 |
| 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 ; 谢兴龙 |
| 关键词 | 高能拍瓦激光装置 啁啾脉冲放大技术 展宽器 光谱剪切 曲率误差 调整误差 光学件加工误差 |
| 其他题名 | Research on the stretcher and the related technique of the high energy petawatt laser system |
| 中文摘要 | 高能量拍瓦（1015W）皮秒（10-12 s）激光装置采用啁啾脉冲放大技术( chirped pulse amplification, CPA)，激光强度达到1019～1021W/cm2，而输出脉冲对比度大于106，主要用来开展惯性约束聚变快点火方案的实验研究。在这类激光装置中，由于要求输出的能量高，一般采用光谱带宽相对较窄但是能够做成大口径的钕玻璃材料作为增益放大介质，这就要求CPA技术中关键器件之一的展宽器提供足够大的啁啾率，而这将导致严重的光谱剪切；同时，为了使输出脉冲具有高的对比度，对展宽器的结构、其中光学件和调整架的参数也都提出了很高的要求。因此，设计一个适用于此类激光装置的展宽器存在不少难点，也直接影响到系统的色散特性和输出脉冲的质量。 本论文主要针对高能皮秒拍瓦激光装置中展宽器的设计开展工作，详细分析了展宽器设计过程中的各种问题，最终设计出高效稳定的展宽系统。论文的主要工作包括以下几个方面： 1．简要介绍了高能拍瓦激光装置中啁啾脉冲展宽的基本原理、展宽器的工作原理和类型，作为例子，详细分析了国际上著名的高能拍瓦激光装置中所使用的展宽器类型和参数。 2．较为系统、详细地对高能拍瓦激光系统各部分的色散特性进行了研究。重新推导了马丁内兹展宽器、Offner展宽器以及一些常用材料的各阶色散表达式，并建立了分析系统剩余色散量对输出脉冲对比度的模型，为改进展宽器的设计提供了理论依据。 3．对展宽器设计过程中遇到的问题进行了专题讨论，并提出了具体的解决方案。具体包括展宽器中非对称光谱剪切问题、展宽器中曲面镜曲率半径误差的问题、展宽器中各器件调整误差的问题、展宽器中各光学件表面加工误差的问题以及系统的色散控制问题，通过对这些问题的深入剖析，为展宽器设计过程中各参数的合理设定提供了依据。 4．根据神光II第九路拍瓦激光装置对展宽器的要求，进行了展宽器的工程设计和实验，其中包括展宽器构型的选择、展宽器基本参数的选择、展宽器各光学件调整架的设计、展宽器调整方案的设计，最后进行了展宽器实验，取得了良好的效果，并达到了设计的要求。 主要创新点表现在：系统分析了高能拍瓦激光展宽器设计过程中的各种问题，为神光II第九路拍瓦激光装置设计了合适的展宽器，实现了系统高对比度和高稳定性对展宽器的要求，具体表现为以下几个方面： 1．展宽器采用八通的Offner结构，在更短的“等效”光栅对斜距离的情况下，实现了大展宽量，从而大大减少了展宽器中的光谱剪切，满足了系统高对比度对展宽器的要求。 2．利用屋脊镜配合法拉第旋光器和半波片使展宽器中四通的光路在原路上来回各走一次，实现了八通的展宽，从而大大降低了调整的难度。 3．分析了展宽器中非对称光谱剪切对输出脉冲对比度的影响，结果显示：对称光谱剪切优于非对称光谱剪切。在展宽器中采用光栅的非中心对称放置来实现对称光谱剪切，以提高输出脉冲对比度。 4．分析了展宽器中曲面镜曲率半径误差对输出脉冲对比度的影响，结果显示：为了满足系统对输出脉冲高对比度的要求，曲面镜曲率半径的误差应该控制在0.2%以内；同时当曲面镜曲率半径存在误差时，应该将凸面镜置于凹面镜的焦点位置，而不是使两者保持同心。 5．分析了展宽器中光学件表面随机误差和调整架调整误差对输出脉冲对比度的影响，从而为展宽器选择合适的光学件加工参数和调整架参数提供了依据。 6．为了实现系统色散的有效调节与补偿，在展宽器的后面加一小压缩器，可以达到全系统色散的小量调节和补偿。 7．在展宽器调整架的设计中，凸面镜调整架的桁架结构采用独特的“日”字形结构，而不是悬臂梁结构，在保证上下不档光的情况下，达到了高稳定性。 |
| 英文摘要 | The chirped pulse amplification (CPA) technique is commonly used to build a high energy, petawatt (1015W) laser facility with the laser intensity up to 1019-1021W/cm2 and the pulse contrast ratio larger than 106, for the purpose of experiment in fast ignition fusion. In such kind of laser system, one has to use Nd:glass, which can be built with a large volume, as the amplification gain medium in order to obtain high output energy. However, the spectral bandwidth of Nd:glass medium is narrow. That is, the stretcher, which is one of the key equipments in the CPA technique, should provide a high rate of chirp. But this results in more serious spectral clipping. Moreover, a high contrast ratio of the output pulse also imposes requirement on the stretcher including the selection of the configuration and the parameters of the corresponding optical elements and adjustment mounts. Therefore, many effects should be considered in designing a suitable stretcher for a ICF laser system and these directly affect the dispersion characteristics of the system and the output pulse quality. This thesis focuses on the design of the stretcher used in the high energy picosecond petawatt laser system. Kinds of problems in the designing are analyzed and a stretcher is proposed for the SHENGUANG(SG) II petawatt upgrade laser facility. And the following topics are mainly included in this thesis. 1． The basic theory of the stretcher system in the high energy petawatt laser facility, including the basic principle of the chirped pulse stetch and the configuration of the stretcher, is briefly introduced. And some stretcher used in the famous high energy petawatt laser facilities are analyzed as examples. 2. The dispersion characteristics of the high energy petawatt laser system are studied in detail. The dispersion formulas, including the Martinez stretcher, the Offner stretcher and some commonly used materials, are re-deducedly. And a model is proposed to analyze the influence of the system residual dispersion on the output pulse contrast ratio, based on which the design of the stretcher can be improved. 3. Several special topics in the designing, such as asymmetric spectral clipping, the manufacture error of the mirror curvature radius, the adjustment error of the optical elements, the manufacture error of the optical surface parameters, and the dispersion control and compensation of the system, are discussed. And the methods to minimize this effects are proposed. Based on these, one can select suitable parameters in the stretcher designing. 4. After the choice of the configuration and the corresponding the parameters of the optical elements and adjust mounts, a stretcher is designed for the SG II petawatt upgrade laser facility. According to the experimental results, this stretcher is suitable for the SG II petawatt upgrade laser facility. The main innovation of the thesis are the follows: kinds of problems in designing a stretcher are discussed systematically; and a stretcher is designed for the SG II petawatt upgrade laser system and satisfies the requirements of the system with a high contrast ratio and high stability, i.e., 1. The stretcher is selected with an eight-pass Offner stretcher configuration, which achieves a larger stretch in the case of a shorter slant distance between the diffraction grating and its image in the stretcher. Then, the spectral clipping is greatly reduced, satisfying the requirement of a high system contrast ratio on the stretcher. 2. The incident pulse will be diffracted double thanks the use of the Farady rotation, and the roof mirrors and the half wave plate. If they are removed, the stretcher reduces to a four pass configuration. That is, the eight-pass stretcher configuration is realized with a four –pass optical configuration. Thus, the difficulty of adjustment is greatly reduced. 3. Effects of asymmetric spectral clipping in the stretcher on the output pulse contrast ratio is analyzed. It is shown that the symmetric spectral clipping has a better contrast ratio than the asymmetric one. In order to keep a symmetric distribution of the spectrum through the stretcher, the grating must be placed on an asymmetric position in the stretcher. 4. The influence of mirror curvature radius manufacture errors on the output pulse contrast ratio is analyzed. It is shown that the errors must be less than 0.2% in order to satisfy the requirement of a high pulse contrast ratio. And it is better to set the convex mirror in the focal point of the concave mirror rather than keeping the two mirrors in the same center, when there exist this errors. 5. Effects of the surface quality and the adjustment precision of the optical elements in the stretcher on the output pulse contrast ratio are analyzed, according to which one can select suitable parameters for the optical elments surface quality and the adjustment mounts. 6. To control and compensate the dispersion of the system, another small compressor can be used in the back of the stretcher. Then small adjustment of the system dispersion can be achieved. 7. A “日”-like structure is introduced for the convex mirror adjustment mount. Then the light can go through the two sides of the convex mirror and high stability is also obtained. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15271]  |
| 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 | 杨庆伟. 高能拍瓦激光展宽系统及其相关技术的研究[D]. 中国科学院上海光学精密机械研究所. 2009. |
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