Attosecond-pump attosecond-probe inner-shell spectroscopy

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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.