Role of spin-orbit coupling in high-order harmonic generation revealed by supercycle Rydberg trajectories
Résumé
High-harmonic generation is typically thought of as a sub-laser-cycle process, with the electron’s
excursion in the continuum lasting a fraction of the optical cycle. However, it was recently suggested that
long-lived Rydberg states can play a particularly important role in high harmonic generation by atoms
driven by the combination of the counterrotating circularly polarized fundamental light field and its second
harmonic. Here we report direct experimental evidence of very long and stable Rydberg trajectories
contributing to high-harmonic generation in such fields. We track their dynamics inside the laser pulse
using the spin-orbit evolution in the ionic core, utilizing the spin-orbit Larmor clock. We confirm their
effect on harmonic emission both via microscopic simulations and by showing how this radiation can lead
to a well-collimated macroscopic far-field signal. Our observations contrast sharply with the general view
that long-lived Rydberg orbits should generate negligible contribution to the macroscopic far-field high
harmonic response of the medium
Domaines
Physique [physics]
Origine : Fichiers éditeurs autorisés sur une archive ouverte
Licence : CC BY - Paternité
Licence : CC BY - Paternité