Time-Resolved Study of Double-Ionization of Atoms

This work is a part of an ongoing project of the time-resolved investigation of the electron-electron correlation in single-photon double-ionization of atoms. The combination of an attosecond-pump-probe set-up and coincidence measurement powered by a reaction microscope (ReMi) is used which provides us with the full kinematic information on attosecond time scale. High harmonic generation is used to produce an attosecond pulse train as a pump which is temporally and spatially overlapped with the fundamental IR eld serving as the probe pulse. By introducing a delay between pump and probe pulses, an interference between photo-electron wave packets is created which serves as an reference to characterize the attosecond pulse train. Finally, the time-resolved study in double-ionization in 2- and 3-particle coincidences is performed

Attosecond Electron-Nuclear Dynamics in Photodissociation of H₂ and D₂

In this work the dynamics of molecular hydrogen (H2) and molecular deuterium (D2) are investigated in a series of kinematically complete experiments on an attosecond time scale using the RABBIT technique. To achieve this, a high-repetition rate attosecond beamline has been designed and constructed. A Mach-Zehnder interferometer configuration is used to perform pump-probe XUV+IR experiments with the help of a sub-8-fs 150-kHz fiber laser to produce XUV light using high harmonic generation. The beamline is combined with a state-of-the-art reaction microscope and coincident electron and ion detection is used to uncover the molecular fragmentation dynamics. The electron localization in the molecular frame of reference in photo-dissociation of H2 and D2 is demonstrated. A semi-classical simulation supports the observed phenomena. The localization of the electron can be manipulated by the number of absorbed photons in the system as well as the delay between the pump and probe pulses. Moreover, phases of the electronic wavepackets in the vicinity of resonant doubly-excited states are extracted, and isotope effects are presented

Multi-Sideband RABBIT in Argon

We report a joint experimental and theoretical study of a three-sideband (3-SB) modification of the "reconstruction of attosecond beating by interference of two-photon transitions" (RABBIT) setup. The 3-SB RABBIT scheme makes it possible to investigate phases resulting from interference between transitions of different orders in the continuum. Furthermore, the strength of this method is its ability to focus on the atomic phases only, independent of a chirp in the harmonics, by comparing the RABBIT phases extracted from specific SB groups formed by two adjacent harmonics. We verify earlier predictions that the phases and the corresponding time delays in the three SBs extracted from angle-integrated measurements become similar with increasing photon electron energy. A variation in the angle dependence of the RABBIT phases in the three SBs results from the distinct Wigner and continuum-continuum coupling phases associated with the individual angular momentum channels. A qualitative explanation of this dependence is attempted by invoking a propensity rule. Comparison between the experimental data and predictions from an R-matrix (close-coupling) with time dependence calculation shows qualitative agreement in the observed trends.Comment: 8 pages, 5 figure

Multi-sideband interference structures by high-order photon-induced continuum-continuum transitions in helium

Following up on a previous paper on two-color photoionization of Ar(3p) [Bharti et al., Phys. Rev. A 103 (2021) 022834], we present measurements and calculations for a modified three-sideband (3-SB) version of the "reconstruction of attosecond beating by interference of two-photon transitions" (RABBITT) configuration applied to He(1s). The 3-SB RABBITT approach allows us to explore interference effects between pathways involving different orders of transitions within the continuum. The relative differences in the retrieved oscillation phases of the three sidebands provide insights into the continuum-continuum transitions. The ground state of helium has zero orbital angular momentum, which simplifies the analysis of oscillation phases and their angle-dependence within the three sidebands. We find qualitative agreement between our experimental results and the theoretical predictions for many cases but also observe some significant quantitative discrepancies.Comment: 9 pages, 6 figure

High-repetition rate attosecond beamline for multi-particle coincidence experiments

In this paper, a 3-dimensional photoelectron/ion momentum spectrometer (reaction microscope) combined with a table-top attosecond beamline based on a high-repetition rate (49 kHz) laser source is presented. The beamline is designed to achieve a temporal stability below 50 attoseconds. Results from measurements on systems like molecular hydrogen and argon dimers demonstrate the capabilities of this setup in observing the attosecond dynamics in 3D while covering the full solid angle for ionization processes having low cross-sections. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen