Researchers at the Max Planck Institute for Nuclear Physics (MPIK) have developed a new experimental approach for tracking the motion of an electron in a strong infrared laser field. The approach is expected to be useful for studying laser-driven electron dynamics within larger atoms or molecules. The team used attosecond transient absorption spectroscopy together with the reconstruction of the time-dependent dipole moment to track the motion of the electron, which was previously developed for bound electrons and is now extended to free electrons. Their paper has been published in Physical Review Letters.

Advantages of the New Method

The new method has a twofold advantage over previous methods. Firstly, it uses XUV single photon ionization instead of tunnel ionization, providing a controllable and well-defined start of the clock. Secondly, the NIR laser can be tuned to low intensities where tunnel ionization is practically not possible any more, allowing the study of strong-field-driven electron re-collision in a low-intensity limiting case.

Counterintuitive Findings

The measurements show that for some experimental parameters, the probability of driving the electron back to the ion can be higher if the light wave is not linearly but circularly polarized. This is a counterintuitive finding that has however been predicted by theorists. Classical simulations performed by the researchers at MPI-PKS in Dresden justify this interpretation, i.e. re-colliding periodic orbits.

The group leader, Christian Ott, is optimistic about the future potential of this new approach. “In general, our technique allows exploring laser-driven electron motion in a new lower-intensity regime, and it could further be applied to various systems, e.g., for studying the laser-driven electron dynamics within larger atoms or molecules.” The new method demonstrated here for helium can be applied to more complex systems for a broad range of intensities.


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