强激光场和原子相互作用中的若干前沿问题研究
文献类型：学位论文
| 作者 | 张敬涛 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐至展 |
| 关键词 | 闽上电离 光电子的角分布 位相相关现象 KaPtiza-Dirac效应 |
| 其他题名 | Study on Several Frontiers of Intense Laser Field Interacting with Atoms |
| 中文摘要 | 超短、超强激光与物质的相互作用及其相关的应用研究是当前国际上现代光学乃至现代物理学中一个非常重要的前沿研究领域。新型超短、超强激光的出现，为光与物质的相互作用研究提供了前所未有的实验手段和极端的物理条件。激光与原子、分子、离子、电子、团簇以及等离子体等各种形态的物质之间的相互作用研究，进入到一个前所未有的高度非线性和相对论的强场范围，具有探远的科学意义和广阔的应用前景。超短、超强激光与物质的相互作用过程中，出现了许多奇特的物理现象。一方面，随着激光强度的不断提高，各种非线性效应不断增强。这些强烈的非线性效应使得传统的微扰理论束手无策，各种新的非微扰理论应运而生；另一方面，随着超短激光脉冲技术的不断发展，实验上已经能够产生高强度的周期量级超短脉冲。这种周期量级超短激光泳冲失去了波动现象所特有的周期性特征，从而导致一系列全新的物理现象与规律，开创出极端非线性相互作用的最前沿，得到了广泛的注意。本论文根据非微扰量子电动力学的理论，在形式散射理论的框架内，研究超强激光场中原子的闽上电离、高次谐波生成，周期量级超短激光脉冲中的位相相关的现象，以及强激光场中电子的Kaptiza-Dirac衍射等，成功地解释了一系列的实验观测结果并预言了若干实验上尚未观测到的现象。本论文取得了一系列创新性科研成果，具体如下：1，研究了单模激光场中，原子闺上电离产生的光电子角分布的特点，阐明了光电子角分布的喷射结构的产生和演化机制，成功解释了若干实验观测。研究表明，喷射结构由复合相位贝赛尔函数的振荡形成，喷射结构的数目等于自变量最大值范围内，复合相位贝赛尔函数的极值数目的两倍；喷射结构与光电子的角动量无关，与初态、中间态的角动量无关；2，得到了决定光电子角分布主要特征的三个基本物理参数，确立了一个新的物理定律一光电子角分布的标度定律。研究表明，光电子的角分布由电离过程中吸收的光子数办有质动力参数up和束缚参数εB唯一地决定；保持这三个参数不变，光电子角分布的主要特点不变，因此光电子的角分布存在标度定律。该定律确立了激光强度、频率及原子结合能与角分布的关系，是强场电离现象的基本规律之一；它使得实验物理学家易于选择可行的实验参数，使理论学家得以确定等价角分布并和实验比较；3，现了奇偶共存的高次谐波的产生机制，阐明了等离子体中奇偶共存的高次谐波的生成机制。研究表明，光电子与激光场脱离的过程中，由于保持能量－动量守恒，将一部分有质动力能及激光能量转化为谐波；4，研究了周期量级超短激光脉冲中绝对位相相关的现象。我们用三模的激光场来模拟超短激光脉冲，对超短激光脉冲与惰性气体原子的相互作用进行了系统的研究，成功地展示了绝对相位对光电子能谱及角分布的影响。研究表明，光电子的分布由脉冲的初始位相、偏振度、脉宽以及光电子的能量等因素共同决定。当其他条件确定时，光电子的分布唯一地由脉冲的绝对位相决定，根据光电子的分布可以确定脉冲的绝对位相；而对于确定能量的光电子，通过调整脉冲的绝对位相、脉宽以及偏振度等可以控制光电子的最优运动方向，实现对光电子的相干控制。5，研究了强场条件下的KaPtiza-Dirac效应。我们用两对激光模来模拟紧聚焦的高斯光场，成功地得到了《Nautre》上Batleaan等人的实验观测结果，预言了有待实验进一步观测的新现象，并确立了发生电子衍射的激光场的临界强度；6，研究了原子在激光场中运动时光场与原子之间的能量交换，以及这种能量在光谱上的反映和对激光场统计性质的影响。研究表明，原子与激光场之间通过光子的吸收和发射交换动量、能量，这种能量交换导致原子的发射谱的分裂，并改变了激光场的光子数统计。当原子的动量与光子的动量可以比拟时，原子质心运动的影响最明显。 |
| 英文摘要 | The interaction of super-intense, ultra-short laser pulses with matters and the related application researches are one of the most important frontiers in modern optics even in modern physics. The availability of new type of ultra-short, super-intense lasers provides an unprecedentedly experimental tool and an extremely experimental condition in the interaction of light with matters. The interaction of laser with matters, such as atom, molecule, ion, cluster and plasma, reaches a higher-order non-linear and relativistic domain, thus is of far-reaching scientific value and wide application foreground. Various fantastic phenomena appear in the interaction of ultra-short, super-intense laser with matters. On the one hand, various nonlinear effects arise along with the increasing laser intensity, which leads to the break-down of the traditional perturbative theories and the emergence of various non-perturbative theories; On the other hand, the recent developments in laser technology have made it possible to produce high-intensity laser pulses of few optical cycles. The few-cycle laser pulses lose the essence of wave, say the periodicity, and lead to a series of new phenomena and roles, which form the newest frontier of the extremely nonlinear interactions and attract much attentions. Based on the nonperturbative quantum electrodynamics theory and in the frame of formal scattering theory, this thesis studies the interaction of intense laser light with atoms and electrons, and focuses on the above-threshold ionization (ATI) and high-order harmonic generations (HHG) of noble atoms, the phase-dependent phenomena in few-cycle laser pulses, and the Kaptiza-Dirac (KD) diffraction of electrons in intense laser fields. This study successfully explains a series of experimental observations and predicts several phenomena for further observation. This thesis includes the following innovative results: 1, We studied the photoelectron angular distributions (PADs) of ATI in single-mode laser, and get the generation and evolution mechanism of jets in the PADs, which explains several experimental observations successfully. Our studies showed that the jet structure are caused by the maxima of the generalized phased Bessel functions, and the number of the jets on one side of the PADs is the twice the number of the maxima of the function in the domain of its variable. It is also found that the jets in the PADs are not determined by the angular momenta of initial and intermediate states; 2, We obtained three basic physical parameters that determine the main features of the PADs, and established a practical scaling law of the PADs. Our studies showed that the PADs are uniquely determined by the photon number absorbed in ionization, the ponderomotive parameter, and the bounding number; and that the PADs are identical provided that these three numbers were kept unchanged. Thus, we concluded the scaling law of PADs, which connects the PADs to the laser frequency, laser intensity, and the atomic bounding energy. The scaling law will be one of the fundamental laws in the field of photo-ionization, which enables the experimentalists to choose viable experimental conditions and the theorists to determine the equivalent PADs and to compare them with observations; 3, We found a new mechanism of HHQ which explains the generation mechanism of the even-odd harmonics in plasma. Our studies showed that the harmonics are generated in the photoelectron exit process. When the photoelectron exit the laser field, part of the ponderomotive energy as well as the laser energy transit into harmonic in order to balance to energy-momentum; 4, We studied the phase-dependent phenomena in few-cycle laser pulses. By means of a non-perturbative quantum scattering theory and employing a three-mode laser field to mimic the short pulse, we study the phase-dependent phenomena in the ATI of noble atoms irradiated by few-cycle pulses, and discuss the probability to the control the photoelectrons. Our studies showed that the PADs in few-cycle laser pulses were determined by the kinetic energy of photoelectrons, the absolute phase of the carrier wave, and the ellipticity and the duration of the short pulses. When other conditions are fixed, the PADs were uniquely determined by the absolute phase, thus one can deduce the value of the absolute phase by the detected PAD. While, for the photoelectrons with fixed kinetic energy, one can control the optimal photoelectron rate by variation of the short pulses; 5, We studied the Kaptiza-Dirac effect in strong field. Using two pairs of standing wave to mimic the tightly focused Gaussian laser beam, we recovered Batelaan et as observation published in Nature, and predicted several new phenomena for further observation. Our theory predicts the minimum value of ponderomotive parameter and the corresponding critical laser intensity, below which no diffraction can occur; 6, We studied the energy transfer of a two-level atom moving in a cavity field, as well as its influence on the atomic emission spectra and on the photon distribution of the intro-cavity field. Our studies showed that the energy transfer induced by the photon emission and absorption is accompanied by the energy-momentum exchange between the atom and the cavity field, which results in the splitting of atomic emission and changes the photon distribution in the cavity. The influence of the atomic motion is more important when the momentum of the atom is comparable to that of photon's. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15566]  |
| 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 | 张敬涛. 强激光场和原子相互作用中的若干前沿问题研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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