报告题目：Attosecond soft-X-ray spectroscopy in the gas and liquid phases
报告人：Prof. Hans Jakob Wörner
主持人：吴健 教授
时间：2019-08-02 15:00
地点：理科大楼A814
主办单位：精密光谱科学与技术国家重点实验室
报告人简介：
Hans Jakob Wöner教授，2007年博士毕业瑞士苏黎世联邦理工学院化学系， 2007年在法国巴黎第十一大学法国国家级重点科研中心(CNRS)从事博士后研究，2007-2010年在加拿大国立研究院阿秒科学联合实验室工作，2010年至今在苏黎世联邦理工大学任教，长期致力于阿秒分子超快动力学方面的基础物理研究，已发表含Nature, Science, PRL等在内的SCI论文共200余篇。
报告内容简介：
Attosecond time-resolved spectroscopy has the potential to address fundamental open questions in chemical sciences. Although the first two decades of research have led to very important advances towards this goal, the techniques of attosecond spectroscopy still need to overcome two gaps. The first gap is the complexity gap, i.e. the challenge of applying attosecond spectroscopy to complex molecules. A promising approach to overcome the complexity gap consists in exploiting the element-, site- and spin-sensitivity of X-ray spectroscopy. We have recently demonstrated the potential of table-top X-ray absorption spectroscopy with a water-window high-harmonic source, observing the temporal evolution of unoccupied molecular orbitals, as well as molecular shape resonances during chemical reactions [1]. Compressing the mid-infrared driving pulses to less than 2 optical cycles, we have demonstrated the extension of this table-top source to fully cover the oxygen K-edge with fluxes sufficient for time-resolved measurements [2]. Using the same technique, we have also demonstrated the generation of isolated attosecond pulses, which have established a new record of the shortest light pulses ever measured (43 attoseconds) [3].
The second gap is the extension from the gas to the liquid phase, which is the relevant phase to the vast majority of chemical and biophysical processes. I will discuss the first observation of extreme-ultraviolet high-harmomic generation from liquids, achieved through the application of ultrathin (0.6-2 m) flat microjets [4]. Exploiting the geometric separation of liquid- and gas-phase harmonics inherent to our experimental geometry, we have observed a nearly linear scaling of the high-harmonic cut-off with the driving electric field, a non-perturbative scaling of all high-harmonic orders and a consistently broader ellipticity dependence of the liquid-phase harmonics compared to the gas-phase harmonics. Finally, I will present the first extension of attosecond time-resolved spectroscopy from molecules [5] to liquids [6], reporting on photoemission delays of liquid compared to gaseous water. The measured time delays range from 50-70 attoseconds and are shown to mainly originate from the solvation of water molecules, with liquid-phase electron scattering playing a minor role. These combined developments set the stage for attosecond time-resolved studies of molecular systems of chemical complexity.