| 题名 | 分子高次谐波产生中的双中心干涉效应 和驱动激光波长效应 |
| 作者 | 尉鹏飞 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 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 | 超短飞秒激光 自动准直 光学参量放大 高次谐波 双中心干涉 |
| 其他题名 | Effects of two-center interference and driving laser wavelength in molecular high-order harmonic generation |
| 中文摘要 | 飞秒激光技术的发展对各个学科领域产生了巨大的推动作用。在物理研究领域，它可以用于探测原子分子中电子和核的超快动力学过程。特别是最近几年，随着宽带可调谐的红外光参量放大 (infrared optical parametric amplifier, 缩写IR-OPA) 激光源的发展，它的输出能量已经能够驱动原子与分子产生高次谐波，而且它的激光波长已经可以调谐到分子振动能级的红外吸收波段，这将为研究甚至控制分子高次谐波过程中的核运动提供了一种全新的手段。 分子高次谐波现象一直是比较热门的研究课题，很多新的实验现象被不断地发现。分子高次谐波的研究，丰富了人们对强场物理过程的认识，加深了人们对微观世界的了解，同时也提供了一种探索微观物质世界的重要手段。 本论文前期的工作旨在为分子高次谐波的研究和阿秒脉冲的产生提供一个先进的驱动激光源和实验研究平台，后期的工作旨在利用该实验平台探测分子高次谐波产生过程中的超快电子和核动力学信息以及研究原子高次谐波产生过程中的阿秒物理。论文的主要结果与创新点包括以下几个方面： 1、设计了一个激光光斑实时监测与光路自动准直装置。自主编写的监测控制程序可以实时监测激光光斑模式与光斑位置的抖动情况，并进行反馈控制。装置的调整精度为0.5μrad，反馈控制频率为1Hz，完全可以降低或消除抖动周期在1s以上的光斑飘动。 2、搭建了一个紧凑的高转换效率而且宽带可调谐的IR-OPA系统。输出的信号光和闲置光的波长调谐范围为1.2μm~2.4μm，最后一级参量放大器的转换效率在0.4μm的宽带调谐范围内达40%。 3、实验上研究了CO2分子高次谐波的角分布调制反转对驱动激光强度的依赖关系。该结果澄清了双中心干涉效应和激光强度效应的各自作用，提出了基于激光强度的复合干涉模型，并演示了双中心干涉效应是可以通过激光强度来实现调控的。 4、实验上分别观测了O2和CO2分子高次谐波的含时演化和角分布信息，并对比了它们的高次谐波干涉增强和干涉抑制过程。实验结果表明了O2分子的双中心干涉同样可以通过驱动激光强度来实现调控。 5、实验上研究了CH4分子和Xe原子在高次谐波产生过程中的波长效应，观测到分子高次谐波产率对驱动激光的波长非常敏感，特别是分子共振吸收附近的波长，而作为对比的具有相似电离势能的原子却对驱动激光的波长不敏感。这个现象可以归因于激光场诱导的轻核运动对分子谐波强度造成的影响。 6、实验上对比了红外双色场驱动的CH4分子和Xe原子的高次谐波产率（双色场为短波800nm加可调谐长波1.5μm ~1.9μm）。实验结果显示，分子红外振动吸收附近的长波成分能够有效地抑制分子高次谐波的产生。 7、实验上使用载波包络相位(CEP)稳定的多光周期(~45fs)的宽带可调谐的IR-OPA系统产生的红外参量激光1.6μm~1.7μm来驱动Ar气产生高次谐波超连续谱，得到的光子能量超过110eV，这为产生高能（甚至水窗波段）阿秒脉冲提供了一个简单可行的方案。 |
| 英文摘要 | Femtosecond laser technology gives impetus to the development in various fields of science. For example, the ultrashort laser pulse can be used in tracing the ultrafast electronic and nuclear dynamics in molecules. In the recent years, with the development of high-intensity and broadband tunable IR-OPA sources for high-order harmonic generation (HHG), the driving laser wavelength can be tuned to the infrared absorption of molecule near the vibrational energy levels, and it is possible to investigate and even to control the nuclear dynamics in the molecular HHG process. Molecular HHG has been intensively explored in the past decade, and many new phenomena in the high-field interaction were discovered. The study on molecular HHG enriches our knowledge on strong field physics. The first part of this thesis aims at establishing an advanced laser system for the investigation of molecular HHG and for the generation of attosecond pulse, and the other part of this thesis aims at tracing the ultrafast electronic and nuclear dynamics in the molecular HHG process and investigating the attosecond physics in the atomic HHG process. Main results and innovation points in the thesis can be summarized as follows: 1.A new device was developed for real-time monitoring laser beam quality and adaptive collimating laser beam direction. The system can collimate the beam direction in a resolution of 0.5μrad and 1Hz adjusting frequency, so it can completely correct the laser beam shift of period longer than 1s. 2.A compact high-conversion-efficiency and broadband tunable IR-OPA system was developed. The tunable wavelength range was from 1.2μm to 2.4μm for both signal and idle pulses. The total OPA efficiency in the last OPA stage reached about 40% in the tunable spectral range of 0.4μm. 3.We experimentally investigated the modulation inversion of angular distribution of HHG from aligned CO2 molecules. The roles of intramolecular quantum interference and the laser intensity were clarified. A laser-field-related recombination interference model was proposed to explain the modulation inversion of harmonic yield. We concluded that the two-center interference in the recombination process can be manipulated by tuning the laser intensity. 4.The enhancement and suppression of HHG were observed in the measurement of both the temporal evolution and the angular distribution from O2 and CO2 molecules. The results indicated that the two-center interference in O2 molecules can also be manipulated by tuning the laser intensity. 5.We experimentally investigated the wavelength effect on HHG in CH4 molecules and Xe atoms, and observed that the molecular HHG around the vibrational resonance was more sensitive to the driving wavelength than HHG from an atomic gas with comparable ionization potential. The results can be attributed to the light nuclear motion induced by the driving laser field. 6.We experimentally investigated the HHG from CH4 molecules and Xe atoms in a two-color field (using the 800nm laser and the tunable laser with the longer wavelength from 1.5μm to 1.9μm). The results indicated that the longer wavelength component around the molecular infrared absorption can suppress the molecular HHG process. 7.High-order harmonic supercontinuum beyond 110eV photon energy was produced in an Ar gas cell by using an IR-OPA based multi-cycle (~45fs) laser source operating at 1.6μm~1.7μm and with passive CEP stabilization. The demonstrated scheme was important for the generation of isolated attosecond pulse at higher photon energy region. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15629]  |
| 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 | 尉鹏飞. 分子高次谐波产生中的双中心干涉效应 和驱动激光波长效应[D]. 中国科学院上海光学精密机械研究所. 2010. |
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