阿秒极端超快高次谐波的理论和基础实验研究
文献类型：学位论文
| 作者 | 曾志男 |
| 学位类别 | 博士 |
| 答辩日期 | 2003 |
| 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 | 高次谐波 超短激光脉冲 阿秒脉冲 共振增强 载波相位 |
| 其他题名 | Theorectical and Preliminary Experimental Study on Ultrafast Attosecond High-Order Harmonics |
| 中文摘要 | 随着激光技术的不断发展，激光脉冲的宽度也越来越窄。从早期的连续波, 纳秒脉冲，皮秒脉冲一直到现在的飞秒脉冲，以及最近正在研究之中的阿秒脉冲，标志着激光与物质的相互作用不断地进入新的领域。由于超短激光脉冲不仅在物理学的研究中有着重要作用（如跟踪原子的超快驰豫过程），而且在其他领域也有着非常广泛的应用（如超高速半导体设备检测，跟踪化学反应过程以及外科手术等）。因此，超短脉冲技术的发展，无论对于科学研究还是应用领域，都具有非常重要的意义。自从1960第一台红宝石激光器发明以来，科学工作者一直在为获得更短的激光脉冲而努力。激光脉宽也一直在不断地缩短，直到1987年获得突破性进展，得到6fs的超短激光脉冲。同时，随着超短超强激光技术的飞速发展，口前在小型化台式激光系统上，可聚焦功率密度已经达到了-1019W／cm~2的量级，在这种功率密度的量级，激光场强度已经远远超过氢原子的内部库仑场强，激光与物质的相互作用已经进入极端非线性的领域。在这种相互作用下，会出现一系列川传统的微扰理论所无法解释的物理现象，如域上电离（Above-Threshold-Ionization，ATI）、高次谐波产生（High一Harmonic一Generation，HHG）等。近几年来，超短激光脉冲与分子、原子和团簇的相互作用研究在包括隶弗莫尔实验室的全世界各个著名实验室如火如茶地进行，在高次谐波的产生、强场原子分子物理、超快X射线辐射、超短波长X射线激光以及小型化高能粒子加速器等研究中取得了日新月异的进展。 近年来，阿秒极端超快过程的研究也获得了极大的进展。M.Drescher等人在实验中用一个飞秒的激光脉冲，采用滤波片在90eV能量附近，直接产生了一个650阿秒的单个阿秒脉冲。他们不仅测量了阿秒脉冲的宽度j而且还用之测量了激光脉冲的载波振荡。本论文工作瞄准阿秒超快过程的前沿研究热点，重点研究了阿秒脉冲的产生过程以及相关的基本物理问题，主要的工作和成果包括以下几个方面：1．研究超短激光脉冲的产生过程，主要是腔外脉冲压缩过程，发现利用毛 细管中的自相位调制过程（S PM），把能量lomJ、脉宽50fs的脉冲压缩到5fs是完全可以的，最终将能够获得ITW的脉冲功率，并讨论了此过程中的自相位调制、介质电离、脉冲能量损耗、气体密度等各参数的影响。2．研究在阿秒脉冲产生过程中，驱动激光脉冲载波相位和脉冲宽度的影 响。发现在载波相位与阿秒脉冲产生位置同步的同时，也存在一定的偏差。发现相邻阿秒脉冲强度比随载波相位的指数变化关系，并在此基础上提出了一种测量载波相位的方法。3．在超短激光脉冲与原子相互作用产生高次谐波过程中，通过采用附加高频场，不仅提出了一种提高高次谐波辐射效率的方法，同时也对双色场高次谐波的产生机制有了进一步的理解。同时发现双色场高次谐波产生过程中原子能级结构对高次谐波产生效率有很大的影响。4．利用全固化飞秒脉冲激光器进行阿秒脉冲产生的基础实验研究，与国外类似工作比较，发现在我们的实验中可能已经在更短的波长（更高的谐波级次）产生了阿秒脉冲链，同时利用小孔研究了激光聚焦特性对高次谐波谱的影响。 |
| 英文摘要 | With the tremendous progress in laser technology, the pulse duration becomes shorter and shorter. The continuous shortening of laser pulse, from the continuum laser output at first, then the nanosecond pulse, the picosecond pulse, to the femtosecond pulse, until the latest attosecond pulse, indicates that the interaction between the laser field and the matter enters into new eras one after another. The ultrashort laser pulse is not only very important in physics, e.g. tracing the relaxation process of electrons, but also widely used in interdisciplinary fields, e.g. detecting the ultrafast process in semiconductor device, monitering the chemical reaction and even carrying out surgical operation. Since the invention of lasers in 1960, many people have been working for shorter and shorter pulses. Begin with the continuum laser, the nanosecond pulse, the picosecond pulse, until the 6fs-pulse obtained in 1987, the pulse duration was shortened again and again. At the same time, with the rapid development of the ultrashort-laser-pulse technology, the focusable intensity of 1019W/cm2 can be realized on a compact table-top laser system, which can support the electric field that is much higher than that in H atom. Under this intensity, it is possible to investigate laser-matter interaction under extreme physical conditions and pave the way to the discovery and the exploration of brand-new physical phenomena, which cannot be explained within the frame of the classical perturbative theory, e.g. HHG and ATI. In past few years, the study of ultrashort super-intense laser interaction with atoms, molecules and clusters has been conducted in a lot of leading laboratories, including Lawrence Livermore National Laboratory, and rapid progress has been achieved in high harmonic generation (HHG), atomic and molecular physics with high intensity lasers, ultrashort x-ray emission, ultrashort wavelength x-ray lasers, compact high energy particle accelerators, etc. Recently, great progress has been made in the research of ultrafast attosecond process. Single 650-attosecond-pulse of 90eV was generated with 7fs driving laser pulse. The subfemtosecond (attosecond) pulse had been used to trace the ultrafast ionization of atoms. The study on the ultrafast attosecond process, including the generation of the attosecond pulse as well as the related fundamental physical proccess, is the main subject of this Ph. D dissertation, the main results are as follows: I. The generation of the ultrashort laser pulse with extracavity compression as the driving laser for attosecond pulse was investigated. It was found that this method is capable of producing a 5fs pulse with the effect of self-phase modulation of a l0mJ, 50fs laser pulse propagating in the capillary filled with the Ne or He gas. We discussed the effect of the self-phase modulation, ionization, energy loss, and the density of the gas. II. For the generation of attosecond high order harmonic pulse, the effect of the carrier-envelope phase and the duration of the few-cycle laser pulse was investigated. We found that although the position of the attosecond pulse is almost synchronous with the carrier-envelope phase, the timing jitter is always existed. We found also that the intensity ratio of the adjacent attosecond pulses changes with the carrier-envelope phase as an exponential function. Based on the phenomena, we proposed a method to in-situ measure the carrier-envelope phase. III. The two-color laser driven HHG was investigated. The effect of the laser intensity, the frequency and the energy level structure of the atom on the efficiency of the two-color HHG was discussed. Resonant enhancement HHG and wave-mixing were found with a high frequency driving laser field. IV. The preliminary experiment of the attosecond high harmonic generation driven with an all-solid-state KHz femtosecond laser system was carried out. Comparing with the recent works, the attosecond pulse chain with shorter wavelength was generated in the experiment. We also investigated the effect of limiting the beam diameter of the driving laser on HHG. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15415]  |
| 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 | 曾志男. 阿秒极端超快高次谐波的理论和基础实验研究[D]. 中国科学院上海光学精密机械研究所. 2003. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。