Bonn 2025 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 21: Poster – Atomic Systems in External Fields
A 21.7: Poster
Mittwoch, 12. März 2025, 17:00–19:00, Tent
Velocity-map imaging of strong-field ionization in standing waves — •Tobias Heldt, Jan-Hendrik Oelmann, Lennart Guth, Lukas Matt, Anant Agarwal, Thomas Pfeifer, and José R. Crespo López-Urrutia — Max-Planck-Institut für Kernphysik, Heidelberg, Germany
To study nonlinear light-matter interactions like multiphoton or tunnel ionization, intense light fields are essential. We employ a femtosecond enhancement cavity to achieve intensities over 1013 W/cm2 at a 100 MHz repetition rate using a near-infrared frequency comb. The bow-tie cavity supports counter-propagating pulses, forming a transient standing wave at the focus. Here, a gas nozzle and velocity-map imaging (VMI) spectrometer are integrated to analyze the angular distribution of emitted photoelectrons [1].
At the antinodes of the standing wave, constructive interference leads to a doubling of the maximum intensity compared to single pulse operation. Additionally, the ionization region along the beam propagation is reduced because it no longer depends on the Rayleigh length but on the < 200 fs overlap of the pulses. This reduction of the focal volume allows momentum imaging without electrostatic focusing [2]. Furthermore, the electrons are diffracted by the structured ponderomotive potential of the standing wave. This phenomenon, known as the Kapitza-Dirac effect, changes the momentum and angular distribution of the photoelectrons.
[1] J.-H. Oelmann et al., Rev. Sci. Instrum., 93(12), 123303 (2022)
[2] T. Heldt et al, Opt. Lett. 49, 6825-6828 (2024).
Keywords: Multiphoton Ionization; Velocity-Map Imaging; Standing Wave; Kapitza-Dirac; Electron Diffraction