Attosecond-pump attosecond-probe inner-shell spectroscopy

多电子动力学和电子关联在包括原子、分子、纳米结构和固体在内的几乎所有物理系统中都是至关重要的。俄歇衰变是电子相关过程的一个纯粹的例子，通常发生在几飞秒的时间尺度上。为了直接在时域中研究这些过程，需要极短的激光脉冲。虽然最简单的俄歇过程是由两个电子之间的相关性引起的，但对于涉及两个以上电子的俄歇过程来说，情况就不一样了。本计画的目标是发展阿秒泵浦阿秒探测内壳层光谱的新方法来研究氙中的多电子俄歇过程，这需要产生强烈的阿秒脉冲。为此，我们将应用最近开发的极紫外（XUV）强度缩放计划的高谐波产生（HHG）使用18米长的光束线。高次谐波将产生氖使用几个飞秒近红外脉冲的目标是产生强烈的孤立的阿秒脉冲在90 eV的区域。两个能量选择的XUV脉冲将产生一个分裂和延迟单元。氙中的内壳层空位将由来自阿秒泵浦脉冲的第一XUV光子的吸收引起。这种内壳层空位的弛豫将被延迟的阿秒探测脉冲探测。利用不同的探测脉冲光子能量，可以研究单、双俄歇过程、俄歇级联过程以及双芯-空穴态的弛豫过程。所得结果将为描述电子关联过程的理论模型提供基准。阿秒泵浦阿秒探测内壳层光谱技术在未来可用于研究原子、分子和固体中电子在极短时间尺度上的动力学。

Multi-electron dynamics and electron correlation are of fundamental importance in almost all physical systems including atoms, molecules, nanostructures and solids. Auger decay is a pure example of an electron correlation process and typically takes place on a time scale of a few femtoseconds. To study these processes directly in the time domain, extremely short laser pulses are required. While the simplest Auger processes as a result of the correlation between two electrons are comparably well understood, the same cannot be said for Auger processes involving more than two electrons. The goal of this project is to study multi-electron Auger processes in xenon by developing the new method of attosecond-pump attosecond-probe inner-shell spectroscopy, which requires the generation of intense attosecond pulses. To this end, we will apply a recently developed extreme-ultraviolet (XUV) intensity scaling scheme for high-harmonic generation (HHG) using an 18-meter-long beamline. High harmonics will be generated in neon using few-femtosecond near-infrared pulses with the goal to generate intense isolated attosecond pulses in the 90 eV region. Two energy-selected XUV pulses will be generated by a split-and-delay unit. An inner-shell vacancy in xenon will be induced by the absorption of a first XUV photon from the attosecond pump pulse. The relaxation of this inner-shell vacancy will then be probed by the delayed attosecond probe pulse. By using different probe pulse photon energies, it will be possible to study single and double Auger processes, Auger cascade processes as well as the relaxation of double core-hole states. The obtained results will provide a benchmark for theoretical models describing electron correlation processes. The attosecond-pump attosecond-probe inner-shell spectroscopy technique can be used in the future for the investigation of electron dynamics in atoms, molecules and solids on extremely short timescales.