飞秒极紫外光场下光电子角分布研究

The character of atomic spatial scale and inherent temporal scale of coherent femtosecond X-ray and extreme ultraviolet light source plays an important role in observing and manipulating atoms, molecules and solid matters, which is of great significance for understanding and controlling light-matter interaction. Among a variety of methods for generating ultrafast XUV light source, high-order harmonic generation (HHG) can provide a table-top tunable coherent light source with a high repetition rate (kHz or MHz), high spatial coherence and femtosecond or even attosecond pulse characteristics, which is available and necessary for detecting electronic quantum state and ultrafast dynamic evolution. The interaction between an intense ultrashort pulsed laser with gaseous atoms or molecules can result in HHG, which generally is a sequence of peaks corresponding to the odd harmonics of the fundamental laser wavelength with an intensity distribution characterized by a plateau. In this project, we will build an experimental setup to investigate ultrafast electronic and structural dynamics in a variety of systems at an energy range and temporal resolution, previously unattainable before. The setup will access a new level on femtosecond or attosecond scale in study atomic and molecular processes. By matching electrical structure in atoms and molecules with XUV light, the pump-probe technique applied with IR pulses will fulfill the measurement of ultrafast dynamics. Compared with other light source, femtosecond XUV pulses will simply the interaction and purified the experimental results. In this study, we build and apply a tunable ultrafast extreme ultraviolet coherent light source based on HHG driving by intense femtosecond laser with Velocity map imaging technique to investigate photoelectron distributions, which is special and obtainable for realizing atomic and molecular dynamics. Evolution of quantum states will be extracted and precisely controlled through this kind of light source.

飞秒极紫外（XUV）光源具有原子级空间分辨和时间分辨的能力，对认识物质世界和控制物理过程具有重要应用。基于超快强场高次谐波产生的桌面化的XUV光源能够在以往不易达到的能量范围和时间分辨率的情况下探测物质的电子结构及动力学性质。本项目计划基于当前发展的高次谐波技术产生超快单波长可调谐极紫外相干光源，结合极紫外光源特性，欲实现飞秒量级的可调协XUV光源对原子分子动力学信息刻画的研究平台。该平台的发展成为在飞秒或阿秒时间分辨尺度上研究或操控原子或分子内电子动力学的新可能。通过结合原子分子量子态结构特征，以超短极紫外单色光源结合近红外光源实现量子态动力学信息的实验研究及演化测量。基于目前发展的桌面化飞秒极紫外光源将成为特色光场调控技术手段，结合速度成像、泵浦探测技术实现该波段的光电子角分布测量，提取量子态动力学演化信息及实现对原子分子内壳层电离过程的精确测控。

超快光场是实现实时观测及调控原子分子内部核和电子超快行为以及其动态演化过程的最佳手段。基于高次谐波产生飞秒量级极紫外光源将可以满足某一量子态的选择制备、激发，从而研究其新型光源作用下的物理规律，同时其飞秒超快特性也将是研究相干动力学演化的必要手段。超短相干的极紫外光源对研究多光子电离过程提供了最基本的“探针”，利用单色的短波源有效的控制原子分子内量子态，从而理解并控制基本物理过程，诸如分波纯态演化测量或者分波间量子干涉。本项目研究了气体高次谐波的产生、优化、单色分光及应用。通过多参量光场调控，实现了谐波光谱的精密操控，并对参量调控下的物理机制进行了分析，发现了原子分子椭偏依赖下的非绝热库仑效应的影响。实验理论结合发现动力学库仑效应对CO2分子谐波产生过程中的电离抑制新机制。分光谐波获得任意单阶谐波光源，结合速度成像技术，实现了任一单色谐波作用下的光电子角分布信息，提取了各向异性参数。针对He原子靶气体，选择15阶谐波，实现了共振中间态的双光子电离角分布测量，分析获得了S/D波量子干涉贡献。针对涡旋场，发展了基于谐波的涡旋光束，同时优化了其匹配条件，获得了极紫外区的短波涡旋场。本项目实现的飞秒极紫外光源应用极大的扩展了强场原子分子量子态的实验调控手段；进一步结合短波涡旋场，通过建立超短涡旋极紫外光源与反映原子分子内部电子运动的光电子成像方法，实现超越常规平面波选择定则的光物质相互作用机理的新发现。