Berlin 2024 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 23: Ultrafast Electron Dynamics at Surfaces and Interfaces III

O 23.6: Vortrag

Dienstag, 19. März 2024, 11:45–12:00, MA 041

Momentum transfer in the pondermotive potential of VIS/NIR laser pulses detected by time-resolved ARPES — •Christian Strüber, Xinwei Zheng, and Martin Weinelt — Freie Universität Berlin, Berlin, Germany

Pump-probe photoemission measurements of ultrafast phenomena at reflective surfaces, e.g. demagnetization process in 3d or rare earth metals detected by tr-ARPES, are affected by the interaction of electrons with the ponderomotive potential of the light field. Oscillatory energy shifts have been detected when the probe laser pulse arrives before the pump pulse [1].

In our time- and angle-resolved photoemission spectroscopy (tr-ARPES) setup [2] using a hemispherical energy analyzer we measure the ponderomotive momentum transfer in dependence of the pump intensity and wave vector, the lateral momentum of the photoelectron and energy of the electronic state in the solid. We employ sub-50fs near infrared-pulses at 1300 nm to create the ponderomotive potential. Extreme ultraviolet pulses at 35 eV allow to detect a large range of lateral and perpendicular momenta. Additional to energy shifts of energetically narrow electronic states we observe squeezing of extended electron wavepackets leading to intensity modulations. Measurement results are simulated and fitted with high accuracy. Complete reversion of the ponderomotive momentum transfer allows for retrieval of the undisturbed initial state.

[1] U. Bovensiepen et al., Phys. Rev. B 79 (2009) 045415

[2] B. Frietsch et al., Rev. Sci. Instrum. 84 (2013) 075106

Keywords: ARPES; photoemission; ultrafast; laser; momentum