Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields

TL;DR

This paper demonstrates the emergence of AC-Stark-shifted resonances in the photo-electron momentum distribution of hydrogen atoms under two-color bi-circular laser fields, revealing symmetry breaking and interference effects.

Contribution

It provides the first detailed analysis of AC-Stark shifted resonances in two-color bi-circular fields and explains their physical origin and dependence on experimental parameters.

Findings

Resonance structures break three-fold symmetry in momentum distribution.

Resonances arise from partial-wave interference between direct and resonant ionization pathways.

Resonant state populations depend on field strength and pulse duration.

Abstract

We report on the appearance of a structure at low energies in the photo-electron momentum distribution of the hydrogen atom exposed to two-color counter-rotating bi-circular laser fields. These structures, which arise due to AC-Stark shifted resonances, break the three-fold symmetry, typical for the $\omega-2\omega$ bi-circular fields. We discuss the physical origin of this structure in terms of partial-wave interference between direct ionization channels and a resonant pathway, that passes through the AC-Stark shifted state and show how the underlying Rydberg state population depend on the field strength and pulse duration.