Freiburg 2024 – scientific programme
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A: Fachverband Atomphysik
A 21: Interaction with Strong or Short Laser Pulses II (joint session A/MO)
A 21.1: Talk
Wednesday, March 13, 2024, 14:30–14:45, HS 1010
Focal volume reduction in pulsed standing waves for xenon multiphoton ionization — •Tobias Heldt, Jan-Hendrik Oelmann, Lennart Guth, Nick Lackmann, Lukas Matt, Fiona Sieber, Janko Nauta, Thomas Pfeifer, and José R. Crespo López-Urrutia — Max-Planck-Institut für Kernphysik, Heidelberg, Germany
To study the highly nonlinear light-matter interaction of multiphoton or tunnel ionization, intense light fields are needed. We use a femtosecond enhancement cavity to fulfill this requirement by reaching intensities of > 1013 W/cm2, even at the high 100 MHz repetition rate of a near-infrared frequency comb. The bow-tie cavity supports counter-propagating pulses, leading to a pulsed standing wave when two pulses overlap in the focus. There, we have integrated a gas nozzle and a velocity-map imaging (VMI) spectrometer to study the angular distribution of the emitted photoelectrons [1].
The joint focus of the counter-propagating pulses leads to a doubling of the maximum intensity. In addition, the ionization region along the beam propagation is also reduced because it no longer depends on the Rayleigh length but on the < 200 fs overlap of the pulses. Our experimental data show that this reduction of the focal volume renders the electrostatic focusing in the VMI technique unnecessary. Furthermore, the standing wave influences the emitted electrons over the structured ponderomotive potential, leading to the Kapitza-Dirac effect.
[1] J.-H. Oelmann et al., Rev. Sci. Instrum., 93(12), 123303 (2022).