| 题名 | 强激光场中小分子体系的高次谐波及解离动力学研究 |
| 作者 | 胡洪涛 |
| 文献子类 | 博士 |
| 导师 | 刘鹏 |
| 关键词 | 分子高次谐波 molecular high-order harmonic generation 氢分子离子解离 dissociation of molecular hydrogen ion 冷靶反冲离子动量成像谱仪 pure even harmonic generation 含时密度泛函理论 time-dependent density functional theory 纯偶次谐波 cold-target recoil ion momentum spectroscopy |
| 其他题名 | High-order harmonic generation and dissociation dynamics of small molecules in intense laser field |
| 英文摘要 | 光与物质的相互作用是世间最奇妙的事物之一。得益于超短脉冲激光技术的发展，科研人员在实验室可以轻易地得到脉冲宽度在飞秒量级、功率密度接近原子内部场强的强场激光。强场激光的优势是可以影响原子核形成的库仑势，直接让原子或分子内部的电子发生电离。正是这一瞬时的电离使得强场物理的现象异常丰富，如电离解离、太赫兹产生、高次谐波、阿秒光学及光电子能谱全息成像等。一方面，这些现象为理解原子分子内部电子的超快动力学提供了可能。更重要的一方面是，这些现象是今后实现对原子分子及其内部电子进行精确操控用来造福人类的重要手段。 激光场与单个原子分子的相互作用是最简单、最理想的情况，也是揭示物理机理的突破口，因而研究气相小分子体系与飞秒脉冲的相互作用具有重要意义。本论文从实验和理论两个方面对气相小分子体系在强场激光中的动力学进行了研究。一方面，应用含时密度泛函理论（Time-Dependent Density Functional Theory，TDDFT）对非对称线性分子产生纯偶次谐波的机理进行了深入研究。另一方面，利用冷靶反冲离子动量成像谱仪（Cold Target Recoil Ion Momentum Spectroscopy, COLTRIMS）在实验上对氢分子离子的解离动力学进行了系统研究。主要内容和创新点包括: 1. 基于从头计算方法TDDFT，首次发现纯偶次谐波可以产生，并对其产生机理进行了深入研究。研究发现当非对称线性分子的分子轴与线偏光的偏振方向垂直时，沿分子轴方向偏振的高次谐波谱只含有偶次谐波。物理机理是由于分子轨道的非对称性，沿分子轴方向偏振的加速偶极矩的相位在每半个光周期里都是一样的，导致不同光周期产生的高次谐波干涉后只剩下偶次谐波。这一工作是完整的高次谐波理论不可缺的一步，并且这种新型的加速偶极矩存在于所有具有永久偶极矩的体系之中，因而这一成果将在强场物理领域有重要应用。 2. 升级了COLTRIMS 系统。例如，搭建了冷靶喷射系统；设计了产生均匀磁场的亥姆赫兹线圈；完善了信号采集和处理等调试工作。使整个系统以良好的状态运行。冷靶喷射系统的搭建大大提高了动量的探测精度，把RIMS变成了真正意义上的COLTRIMS。亥姆赫兹线圈的设计加工的完成标志着不久的将来我们就可以实现离子-电子符合测量。这些工作为后续相关实验的展开打下了坚实基础。 3. 利用COLTRIMS，系统地研究了氢分子离子在不同光强和波长的强场激光中的解离动力学。实验发现随着超短脉冲波长（800 nm，1400 nm 和1800 nm）的增加，氢离子（氢分子离子解离的产物）携带的动量在减小；随着光强的提高，多光子解离通道产率的增加明显大于单光子解离通道。在少周期光（6 fs, 800 nm）的泵浦-探测实验中也观测到了与单束光实验相符的氢离子动能的移动。从质子动能谱随波长和光强的变化证明了强激光场中氢分子离子振动态选择解离可以实现。我们还应用双色场实现了超过50% 的解离几率的调制。; Light-matter interaction is one of the most beautiful and wonderful things in the world. Benefit from the development of ultrafast pulsed laser technology, researchers can easily obtain a intense laser pulse with the duration as short as femtosecond and the intensity as high as 1015~ 1016 W/cm2, which close to the internal field strength of atoms, in the laboratories all over the world. The advantage of the intense laser is that it can influence the Coulomb potential formed by the nucleus, and directly ionize the electrons in the atoms and molecules. It is this ionization that makes the phenomenon of intense laser field physics extremely rich, such as dissociation, terahertz generation, high-order harmonic generation, attosecond science and photoelectron spectroscopy holographic imaging. On the one hand, these phenomena provide a possibility for understanding the ultrafast dynamics of electrons within atoms and molecules. More importantly, these phenomena are important tools for the future precise manipulation of atoms and molecules and theire internal electrons for the benefit of mankind. The interaction between laser and single atom or molecule is the simplest (most ideal) situation, and it is also a way to reveal the mechanism of physics behind the phenomena, so it is of great significance to study the small molecular system of gas phase. In this paper, the dynamics of small molecules in intense laser field is studied experimentally and theoretically. Firstly, the mechanism of pure-even harmonics generated from asymmetric linear molecules is studied by using the Time-Dependent Density Functional Theory (TDDFT). Secondly, the dissociation dynamics of hydrogen molecule ions are systematically studied employing the Cold-Target Recoil Ion Momentum Spectroscopy (COLTRIMS). The main contect and innovations are listed as follows. 1. Based on the ab initio method, TDDFT, the generation of pure even harmonics is studied deeply for the first time. We found that the pure even harmonics will generated with the polarization along the direction of molecular axis, when the molecular axis is perpendicular to that of laser polarization. The physical mechanism is a new accelerated dipole moment. This new accelerated dipole moment exists in all systems with permanent dipole moment, so it may become one of the most important applications in the field of intense laser physics. 2. Built up the cold-target injection system of COLTRIMS. Designed the Helmholtz coils to produce a uniform magnetic field. Improved the signal acquisition and processing and other debugging work, and made the whole system in a good state of operation. The construction of cold target injection system greatly improves the detection precision of momentum, and turns RIMS into a real COLTRIMS. The completion of the Helmholtz coils marks the near future in which we can achieve ion-electron coincidence measurements. 3. The dissociation dynamics of H2+ in intense laser fields is systematic investigated. Mainly focus on how the kinetic energy spactrum of dissociation proton can be modulated by the wavelength (800 nm, 1400 nm, 1800 nm) and intensity of the driving laser field. It was found that the kinetic energy spectrum of H+ shifts to lower kinetic energy with increasing wavelength under the same intensity, and the ratio of ATD/BS increases with the increasing of laser intensity. The intensity effect is also observed in the few-cycle (6 fs, 800 nm) pump-probe experiment. The wavelength- and intensity-dependent proton spectra reveal the mechanism of selective excitation of vibrational levels of H2+ in intense laser fields. The probability of photodissociation of H2+ is also strongly modulated (>50%) by using a two-color laser field. |
| 学科主题 | 原子与分子物理 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31110]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 胡洪涛. 强激光场中小分子体系的高次谐波及解离动力学研究[D]. |
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