Rostock 2019 – scientific programme
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A: Fachverband Atomphysik
A 15: Attosecond physics
A 15.3: Talk
Wednesday, March 13, 2019, 11:15–11:30, S HS 3 Physik
Analysis of sub-cycle XUV-NIR-induced excitation dynamics in helium by UV photoelectron spectroscopy — Jesse Klei1, Renate Pazourek2,3, Christian Neidel1, Arnaud Rouzee1, Martin Galbraith1, Mette Gaarde2, Ken Schafer2, Marc J. J. Vrakking1, and •Jochen Mikosch1 — 1Max-Born-Institut, Berlin, Germany — 2Louisiana State University, Louisiana, USA — 3University of Technology, Vienna, Austria
We use UV photoelectron spectroscopy to study the excitation dynamics of 1snp neutral states in helium from XUV-NIR excitation with an attosecond pulse train and a co-propagating NIR field. The excited state population is found to oscillate with the XUV-NIR delay at twice the NIR field frequency. We measure the phase of the 1s3p population oscillation with respect to the oscillating NIR-dressed ionization yield related to the 17th harmonic order, as a function of energy shift of the XUV frequency comb. Numerical TDSE calculations are performed and found to be in good agreement with the experimental results. The observed oscillation of the 1s3p population is the result of interference between two independent two-color excitation channels, which are out-of-phase: Apart from the previously identified NIR-assisted interference of excitation pathways involving the 15th and the below-ionization-threshold 13th harmonic, we find the phase-shifted interference of excitation pathways involving the 15th harmonic and the above-ionization-threshold 17th harmonic to contribute to the 1s3p excitation yield. Importantly, the relative yield of the two channels is found to depend on the frequency comb spectral position.