| 题名 | 拍瓦级激光系统性能提升中的若干问题研究 |
| 作者 | 於亮红 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 梁晓燕 |
| 关键词 | 拍瓦 啁啾脉冲放大 光参量啁啾脉冲放大 YCOB LBO |
| 其他题名 | Study in several key issues related to the development of Petawatt-level laser system |
| 中文摘要 | 自1985年啁啾脉冲放大（CPA）理论提出后，超短超强激光系统经过几十年的发展，其峰值功率达到太瓦（10 12 W）甚至拍瓦（10 15 W）量级， 聚焦峰值功率能够达到10 21 W/cm 2 -10 23 W/cm 2 。这种超短超强激光为众多 学科领域提供了前所未有的实验手段和极端物理条件，因此被广泛地应用 于超强场激光物质相互作用的实验中，比如，超快X射线辐射、高次谐波 的产生、激光尾波场粒子加速和快点火激光核聚变等实验中。对于绝大多 数超强场激光物质相互作用实验来说，起决定作用的是激光聚焦后焦点处 的峰值功率密度。焦点的峰值功率密度主要由激光单脉冲能量，脉冲宽度 和焦斑大小决定的。所以，获得高能量、窄脉宽、近理想聚焦光斑的超高 功率激光是本领域的研究热点。 本论文的工作瞄准于拍瓦级激光系统性能提升中的若干问题，主要工 作包括基于YCOB和LBO晶体的较大能量、宽带、非共线光参量啁啾脉 冲放大（OPCPA）理论和实验研究，基于Φ80mm 口径钛宝石CPA 激光 系统1.26PW实验研究以及超强超快激光波前校正和可聚焦特性研究等方 面。主要研究成果包括以下几个方面： (1). 开展基于YCOB和LBO晶体的较大能量、宽带、非共线OPCPA理 论和实验研究。在理论上，我们建立YCOB和LBO晶体的非共线 OPCPA的理论模型，数值模拟结果表明在527nm泵浦800nm宽带OPCPA中，YCOB晶体能够支持130nm的宽带放大，LBO能够支持 102nm宽带放大。实验方面，在527nm/2.85ns的激光脉冲泵浦下，对 基于中等口径YCOB或LBO晶体高能量宽带OPCPA的放大性能，包 括增益、转换效率、增益带宽、参量荧光以及光束质量等一系列关键 科学技术问题进行研究，解决了高量级OPCPA的科学难点和工程技 术问题。在中心波长800nm附近，YCOB获得带宽为49nm，单脉冲 能量为3.36J的输出，相应的转换效率达到9.6%，压缩后脉宽为43fs。 3.36J是通过OPCPA技术在800nm波段附近获得的最高能量输出。经 进一步优化泵浦光和信号光的功率密度和时空匹配，在YCOB晶体和 LBO晶体上获得最高转换效率超过20%。实验证明YCOB和LBO晶 体，是除了钛宝石以外，能在中心波段为800nm附近实现高能宽带放 大的优良介质，可应用于10PW超高功率激光系统的终端放大器。 (2). 完成了基于钛宝石CPA技术的1.26PW拍瓦激光实验研究，将原有的 0.89PW/29fs的输出提升至1.26PW/29fs。本实验在原有拍瓦泵浦源的 基础上，优化泵浦输出性能，提升泵浦输出能量，实现双路高能量输 出，特别是优化泵浦光和信号光的时空匹配精度，有效提升钛宝石横 向寄生振荡的抑制能力。以尺寸为Φ80mm×32mm钛宝石为放大介质， 在105J泵浦的能量下，获得最高能量50.2J的输出，压缩后能量脉冲 能量为35J，脉宽为29fs，单脉冲峰值功率为1.26PW，是国内基于80mm 口径钛宝石的最高输出能量。 (3).开展超强超快拍瓦激光波前校正和可聚焦特性研究。利用自适应光学 技术，采用近焦点球面波前校正新方法对0.89PW/29fs激光系统进行 波前校正，成功的获得较为理想的波前分布和接近衍射极限的聚焦光 斑。校正后聚焦光斑大小为6.34×6.94um 2 （对应1.63×1.78倍的衍射 极限），焦点聚焦峰值功率密度提高6倍，达到2.59×10 21 W/cm 2 。通 过模拟和实验证明，该方法不像传统的波前校正方法对波前探测器和 变形镜的位置有严格的成像要求，对两者偏离成像位置有一定的容忍 度，使得该方法操作简单。利用近焦点球面波前校正方法仅用Φ60mm 口径的可变形镜就能对拍瓦激光系统波前进行校正，是提高激光聚焦 功率密度的经济简单而有效的方法。 |
| 英文摘要 | Since the advent of Chirp-pulsed Amplification(CPA) technique in 1985, the development of the ultrashort ultraintensity laser system is rapidly in the past several decades and the peak power is up to terawatt level, and even to patawatt level now. The intensity of focus is up to 10 21 W/cm 2 to10 23 W/cm 2 . The ultrashot ultrahigh laser systems provide unprecedented methods and extreme condition for physical experiment, so the lasers are widely used in the laser-matter interaction experiments, such as ultrafast X-ray radiation, ultrahigh-order harmonic generation, laser wakefield particle acceleration and fast ignitor fusion, and so on. For the most laser-matter interaction experiments, the focus plays a decisive role and the focus intensity is most important physical quantity. The focus intensity is decided by pulse energy, pulse duration and the focus size. So, to obtain an ultrahigh power laser pulse with high energy, ultrashort duration and near diffraction-limitation beam quality is the hotspot in the research area related to ultrashort ultrahigh power laser system This paper is aimed at several key issues related to the development of Petawatt-level system. The main works include the study in high energy, broadband and non-collinear OPCPA based on YCOB and LBO crystal in theory and experiment, 1.26PW output based on Ti:sapphire and CPA laser system, the design for 10PW base on the Hybrid CPA and OPCPA and study in wavefront correction and focusing capability of petawatt laser. The main innovative results have been summarized as follows: 1. Carry out high energy, broadband and noncollinear OPCPA based on YCOB and LBO crystal in theory and experiment. In theory, we built the theoretical model of noncollinear OPCPA based on YCOB and LBO. The results of simulation show that YCOB and LBO can support 800nm broadband OPCPA pumped by 527nm. In experiment, we studied the characteristics of high-energy broadband OPCPA based on YCOB and LBO, including the study in gain, conversion efficiency, gain bandwidth, OPG, beam qulity and other key issues about OPCPA. We also solved some difficulties in science and technology about high-energy OPCPA. Based on a Ti:sapphire chirped-pulse amplification front end, an amplified signal energy of 3.36 J was generated with a pump of 35 J in the YCOB crystal. Compressed pulse duration of 44.3 fs, with a bandwidth of 49 nm, was achieved. This is the highest energy near 800nm obtain by OPCPA. Conversion efficiency of YCOB-OPCPA and LBO-OPCPA is more than 20% after optimizing the pump energy and matching in time and space between the pump and signal light. The results confirm that YCOB and LBO crystal are another good mediums besides Ti:sapphire, which can used in broadband amplification in 800nm, and they can be used in 10PW laser system as the finial amplifer. 2. Improving the peak power of patawatt laser system from 0.89PW/29fs to 1.26PW/29fs. We optimized the out performance of 0.89PW pump laser system to improve the energy of pump pulse. We also optimized the time and space matching between the pump and the signal to improve the ability of Parasitic lasing suppression in high gain femtosecond petawatt Ti:sapphire amplifier. A maximum output energy of 50.8 J is achieved at a pump energy of 105 J base on a Φ80mm Ti:sapphire, which corresponds to a conversion efficiency of 47.5%. Based on the existing compressor, the laser system achieves a peak power of 1.26PW with 29fs pulse duration, which is the highest output peak power based on a Φ80mm Ti:sapphire in home. Combination the advantanges of CPA and OPCPA, we suggest an new design of 10PW in which CPA as the front amplification and OPCPA as the main amplification. 3. Carry out the wavefront correction and improve the focusing ability of petawatt laser system. Based on the adaptive optics (AO) technique, a new method named spherical wavefront correction near the focus was used to correct the wavefront aberration of 0.89PW/29fs laser system and achieved a quite pefect wavefront and a near diffication limitation (DL) focal spot. After correction，the size of focal spot is about 6.34×6.94um 2 (1.63×1.78 DL) and the peak intensity in focal spot is about 2.59×10 21 W/cm 2 which is 6 times as much as it before correction. The method of spherical wavefront correction near the focus is tolerant to the difference phase conjugation precision. This method is a economical, easy to use and effective method to improve the intensity of focal spot. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15763]  |
| 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 | 於亮红. 拍瓦级激光系统性能提升中的若干问题研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
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