高强度周期量级超短激光脉冲的产生及关键技术研究
文献类型：学位论文
| 作者 | 陈晓伟 |
| 学位类别 | 博士 |
| 答辩日期 | 2007 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李儒新 |
| 关键词 | 飞秒激光脉冲 非线性传输 脉冲自压缩 周期量级激光脉冲 成丝 |
| 其他题名 | Study of Intense Few-cycle Ultra-short Laser Pulse Generation and Related Technologies |
| 中文摘要 | 近些年来，阿秒（10-18s）脉冲的产生以及利用阿秒脉冲进行超快物理现象研究成为国际上激光物理领域的研究热点。自2001年首次成功获得脉宽为650阿秒的单个亚飞秒级相干软X射线脉冲以来，阿秒科学领域迅速发展，最近人们又实现了对原子隧穿电离过程的阿秒尺度实时观测，这说明人类已经进入了研究原子内电子运动过程的“阿秒物理学”时代。目前，已有的理论与实验研究已证明利用载波包络相位（CEP）稳定的周期量级超短激光脉冲驱动惰性气体产生高次谐波是获得稳定单个阿秒脉冲的有效手段，因此，获得高强度周期量级超短激光脉冲成为促进阿秒领域进一步发展的重要工具。 本论文基于本实验室承担的阿秒研究项目，针对高强度周期量级超短激光脉冲的产生及相关问题开展了一系列实验与理论研究工作，探索超短激光脉冲在透明介质中的非线性传输现象，发展较高能量飞秒激光脉冲压缩的新原理新方法，建立周期量级极端超快强场激光物理实验平台，为阿秒科学研究以及极端超快条件下激光脉冲与物质的相互作用研究提供必要而有力的实验工具。论文的主要工作与创新点包括以下几个方面： 1．首次在实验上观察到高强度飞秒激光脉冲在正色散透明固体介质中的自压缩现象，实现将50fs激光脉冲自压缩至20fs，对应2.5倍压缩因子，并详细研究了不同实验条件下脉冲的自压缩行为。实验结果表明脉冲自压缩量随入射脉冲强度的增加呈递增趋势，然而当入射光强增大到足以引起锥形辐射产生时，脉冲时域包络会发生分裂。此外还发现发散光束入射情况下同样可以观察到脉冲自压缩现象。 2．利用高重复频率（1kHz）、GW量级飞秒激光脉冲实验验证了高强度飞秒激光脉冲在空气中的自压缩现象，研究了入射脉冲在不同初始啁啾条件下经空气中聚焦成丝后时域及频域特性随入射脉冲能量的变化规律。实验结果表明，在无需后继色散补偿情况下，高强度飞秒脉冲仅通过在空气中的非线性传输过程就可以实现脉冲压缩；在入射脉冲为负啁啾情况下，实验观察到脉冲光谱及时域宽度同时得到压缩，并可获得比驱动脉冲更短的近双曲正割型变换限脉冲。 3．实验和理论研究了入射脉冲峰值功率接近介质自聚焦阈值功率条件下高强度飞秒激光脉冲在氩气中的自压缩现象。基于非线性薛定谔传输方程，我们对飞秒激光脉冲在氩气中的传输过程进行理论模拟计算，并详细研究了不同物理机制对脉冲特性变化的影响。研究表明多光子电离效应与自陡峭效应均可引起脉冲宽度的自压缩，然而在传输过程中这两种效应在不同光强度阶段起主导作用，自陡峭效应是促使形成最终脉冲自压缩的关键因素。在选择合适的几何聚焦参数条件下可延长自陡峭效应在传输过程中的作用距离，从而获得短至一两个光周期的自压缩脉冲。 4．采用两级惰性气体成丝压缩技术成功获得CEP稳定的0.7mJ、5fs超短激光脉冲，是目前为止国际上采用成丝压缩技术获得的最大能量周期量级超短脉冲。实验中我们发现在光束聚焦之前用软边光阑进行光束空间整形可有效抑制多丝的形成，并维持稳定的单丝传输模式。最终输出的压缩光束具有良好的空间均匀性与聚焦能力，这使其成为强场激光物理研究中的重要实验工具。 5．采用充惰性气体空心光纤压缩技术成功获得CEP稳定的0.52mJ、5fs超短激光脉冲，目前已应用于强场激光物理实验中，获得稳定的高次谐波输出。 6．提出并实验验证了以透明固体材料为非线性光谱展宽介质进行较高能量飞秒脉冲压缩的新方法。使光束进入固体介质之前在惰性气体中形成一小段成丝，此方法可有效改善光束空间质量，相应地减小输出光束的空间啁啾，并有助于得到更宽的光谱。经过啁啾镜进行色散补偿，我们成功将32fs驱动激光脉冲压缩至15fs，整个压缩系统的能量效率高于80％，此方法可适用于更高能量飞秒激光脉冲压缩。 |
| 英文摘要 | Attosecond (10-18s) pulse generation and its applications in the research of ultra-fast phenomena attract a lot of attentions in recent years. The field of attosecond science develops rapidly since the first generation of single 650as coherent soft X-ray pulse in 2001. Very recently attosecond real-time observation of electron tunneling in atoms was realized. These researches show that a new era of “attosecond physics” is coming. An effective method to produce single attosecond pulses is the high-order harmonic generation (HHG) by using carrier-envelope phase (CEP) stabilized few-cycle ultra-short laser pulses to drive rare gases. Therefore, high-intensity few-cycle ultra-short laser pulse is a crucial tool to promote the further development of the field of attosecond physics. In the frame of the attosecond research project of our laboratory, we carried out a series of experimental and theoretical investigations relevant to the generation of high-intensity few-cycle ultra-short laser pulse and related problems, exploring the nonlinear propagation phenomena of the ultra-short laser pulse in transparent media, developing new theory and new methods on high-energy femtosecond laser pulse compression, and constructing few-cycle experimental platform for ultra-fast high-field laser experiments. Main work and innovative points of this thesis are as follows: 1. The self-compression of high-intensity femtosecond laser pulses in the transparent solid medium with positive dispersion was demonstrated experimentally for the first time, and the self-compression of laser pulses from 50fs to 20fs was realized, corresponding to 2.5 times compression rate. The self-compression behavior was investigated in detail under a variety of experimental conditions. The temporal and spectral characteristics of compressed pulses were found to be significantly affected by the input pulse intensity, with higher intensity corresponding to shorter compressed pulse. However, the output pulse was split into two peaks when the input intensity was high enough to induce conical emission. Moreover, we found that pulse self-compression could also be achieved with a divergent input laser beam launched into the solid medium. 2. Pulse self-compression in air was experimentally demonstrated by using 1kHz femtosecond laser pulses with input power at the order of GW. Under the conditions of different initial chirps, the temporal and spectral characteristics of the output pulse after being focused in air are studied in detail as a function of input pulse energy. The experimental results show that, the temporal duration of high-intensity femtosecond laser pulses could be shortened through the nonlinear propagation in air, without any additional dispersion compensation. Moreover, with negatively chirped input pulses, we observed that the spectrum and pulse duration could be compressed simultaneously, and near sech2 transform-limited output pulses shorter than original laser pulses were obtained. 3. Self-compression of femtosecond pulses in argon gas with the input power (Pin) close the self-focusing threshold (Pcr) has been investigated experimentally and theoretically. Based on the extended nonlinear Schrödinger (NLS), we theoretically simulated the pulse propagation in argon gas, and investigated the effect of different physical mechanisms on the pulse characteristics in detail. It was demonstrated that either multiphoton ionization (MPI) or self-steepening effect can induce pulse shortening, but they predominate under different beam intensities during propagation. It is the latter effect that is the key player for the final pulse self-compresseion. By choosing a proper focusing parameter, the action distance of the space-time focusing and self-steepening effects can be lengthened, which can promote a shock pulse structure with a duration short to one or two optical cycles. 4. CEP stabilized optical pulses at 1kHz with duration of 5fs and energy of 0.7mJ have been generated through cascade filamentation compression technique, which is so far the highest energy of two-cycle compressed pulses by using this method. In this scheme, a simple and effective method is developed to suppress multiple filament formation and stabilize single filament by using a soft aperture to spatially shape the driving laser beam prior to focusing, resulting in an excellent compressed beam quality. The good beam quality and potentially higher peak power make this ultra-short laser pulse source a significant tool for high-field physics applications. 5. The generation of CEP stabilized 0.52mJ、5fs ultra-short laser pulses at 1kHz has been successfully demonstrated by using gas-filled hollow fiber technique, which has already been applied in the HHG experiments as the driving source. 6. A novel technique for high-power extracavity pulse compression is proposed and experimentally demonstrated with a transparent solid material as the nonlinear medium. Before spectral broadening through self-phase modulation in the solid material, a short distance of filament generated in argon is used as a spatial filter, which not only leads to an effective improvement of spatial beam quality, but also promotes a stronger spectral broadening. Compensated by chirped mirrors, 15fs pulses are generated from 32fs input laser pulses, and the energy efficiency of the total compression system is higher than 80%. This technique can be used for femtosecond laser pulse compression with higher energy. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15413]  |
| 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 | 陈晓伟. 高强度周期量级超短激光脉冲的产生及关键技术研究[D]. 中国科学院上海光学精密机械研究所. 2007. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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