| 题名 | 阿秒级XUV相干辐射产生的理论与实验研究 |
| 作者 | 郑颖辉 |
| 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 | 超短激光脉冲 高次谐波 阿秒脉冲 偏振时间门 位相延迟优化 |
| 其他题名 | Theoretical and Experimental Study on the Generation of Attosecond XUV Coherent Radiation |
| 中文摘要 | 自上个世纪八十年代初以来，时间的计量和时间过程的分辨率进入了飞秒(10-15s)级超快时间尺度时代。飞秒超快激光技术对科学技术的各个领域产生了巨大推动，它不仅可以用于研究分子中原子的超快运动过程，而且在其他领域也有着非常广泛的应用，比如跟踪化学反应过程、超高速半导体设备检测以及外科手术等。九十年代中期以来，新型超强超短脉冲激光的出现与迅猛发展，为人类提供了前所未有的全新的实验手段与极端的物理条件。超强超短激光与物质相互作用的深入研究，为阿秒级XUV相干光源的产生提出了全新的思想与方法，从而使人类最终突破飞秒的壁垒，开创出阿秒光谱学、阿秒物理学乃至阿秒科学技术的全新学科与未来高新技术领域。 近年来，阿秒级XUV相干光源的产生与应用研究获得了极大的进展。2001年，M. Drescher等人首次成功产生脉宽为650阿秒的单个阿秒脉冲(光子能量为90eV)。2002年该研究小组首次利用亚飞秒单脉冲研究了被激发的氪原子内电子云的超快运动过程，实现了小于1飞秒的测量精度，以此为标志，人类正式由研究分子中原子运动的“飞秒化学” 时代进入到研究原子内电子运动的“阿秒物理学”时代。2006年意大利科学家进一步将单个阿秒脉冲宽度推进到130阿秒。阿秒相干光源的产生与应用领域正待开拓与发展，无论在理论、实验研究还是应用开拓上都正处在出现重大突破的前夜。 本论文工作瞄准阿秒极端超快过程的前沿研究热点，重点研究了阿秒级XUV相干辐射的产生以及相关的基本物理问题，特别是在探索突破100阿秒大关的新机制原理实验研究中取得了突破性进展，主要的研究进展与创新成果包括以下几个方面： 1.研究了XUV阿秒脉冲在高次谐波产生过程中引起的非偶极效应，发现考虑了激光场的空间不均匀性后谐波强度降低，谐波频率向低级次移动，电子能谱的能带内出现了更多的光电子峰，并讨论了此过程中阿秒脉冲的波长、红外基频光的光强等参数的影响。 2.对利用偏振控制时间门技术产生高次谐波实验中观察到的光谱干涉现象的物理机制进行了理论和实验研究，提出了与前人不同的解释。我们研究发现，谐波谱上的条纹是用于构造时间门的波片后具有一定延迟的两个脉冲产生的光谱干涉的直接体现。通过改变两个λ/4波片的角度、多级波片引入的延迟以及驱动激光的光强可以控制光谱干涉条纹的可见度。 3.在实验上利用7fs/800nm激光脉冲驱动较长气体介质，获得了可以支持脉冲宽度小于100阿秒单个阿秒脉冲产生的高次谐波平台区连续谱，初步研究表明其产生机制与时间相关的宏观相位匹配过程有关。 4.实验上演示了用位相延迟优化的7fs/800nm和37fs/400nm的双色激光场产生了同时展宽和增强的高次谐波超连续谱。在特定的延迟范围内，通过调节基频和倍频激光脉冲之间的相对延迟可以连续地改变连续谱的谱宽和强度，提出了脉冲宽度和强度可调的阿秒脉冲产生新方法。 |
| 英文摘要 | Since early eighties in last century, time measurement and time resolution have entered into the era of femtosecond (10-15s) ultrafast time scale. Femtosecond ultrafast laser technology gives impetus to the development in various fields. The ultrashort laser pulse can be used not only in tracing the ultrafast atomic motion in molecules, but also widely in interdisciplinary fields, e.g. monitering the chemical reaction, detecting the ultrafast process in semiconductor device and even carrying out surgical operation. Since the mid nineteen nineties, the emergence and rapid development of new ultrashort laser pulse have provided completely new experimental instruments and conditions which are never seen before. The interaction between the ultrashort laser field and the matter brings new ideas and methods in the generation of ultrafast attosecond coherent source, breaks through the obstacle of femtosecond, and cuts the way to the attosecond spectroscopy, attosecond physics and new subjects in attosecond technology. Recently, great progress has been made in the research of attosecond coherent radiation and applications. In 2001, single 650as pulse of 90eV was generated with a 7fs driving laser pulse by M. Drescher et al.. In 2002, they traced the ultrafast motion of electron cloud in krypton atom excited by single sub-femtosecond pulse and realized the precision less than 1fs, which indicates the coming of attosecond physics age. In 2006, the Italian scientists obtained the 130as single attosecond pulse. The research in attosecond generation and application is on the eve of achieving great breakthrough. The study on the ultrafast attosecond process, including the generation of the attosecond XUV coherent radiation especially the sub-100as attosecond pulse as well as the related fundamental physical process, is the main subject of this Ph. D dissertation. Main progress and innovative results of this thesis are as follows: 1.The nondipole effects in the high-order harmonic generation caused by the short wavelength of XUV attosecond pulse which is comparable to the scale of spreading electron wavepacket are investigated. It is found that, in the case of considering the nondipole effects, the harmonic yield is lower than that of dipole approximation with a shift of the frequency towards lower order harmonics, and that more photoelectron peaks appear in the energy band of the photoelectron spectrum. The effects of the wavelength of attosecond pulse and the driving laser intensity are also discussed. 2.We investigate the underlying physics of the spectra interference in the high-order harmonic spectra generated in a gas cell driven with the polarization-modulated infrared laser pulses both experimentally and theoretically. The conclusions we draw in this work are different from the explanations that have ever been proposed by others. We find that the fringes in the harmonic spectra are a direct exhibition of the spectral interference caused by the two outgoing pulses with a delay after two wave plates. We can also control the interference visibility by changing the angles of the two quartz wave plates, the time delay introduced by the multiple-order wave plate, and intensity of the driving laser field. 3.The high-order harmonic continuum in the plateau is demonstrated in an 4.5mm-long gas cell driven by 7fs/800nm phase-stabilized ultrashort intense laser pulse. It is promising to obtain isolated sub 100 attosecond pulses with subsequent amplitude and phase control of the supercontinuum ranging from plateau to the cutoff region of the high harmonic spectrum. It is found that the achievement of the plateau continuum is related to the phase matching by preliminary research. 4.We experimentally demonstrate the XUV supercontinuum generation with broadened bandwidth and enhanced intensity, by using the two-color laser field with a few-cycle fundamental laser pulse and with a controlled relative phase between the two pulses. The spectral width and the intensity of the generated continuum can be continuously varied in a special range by simply adjusting the time delay between the two color pulses. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15416]  |
| 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 | 郑颖辉. 阿秒级XUV相干辐射产生的理论与实验研究[D]. 中国科学院上海光学精密机械研究所. 2007. |
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