Sub-barrier pathways to Freeman resonances

Abstract

The problem of Freeman resonances [R. R. Freeman \textit{et al.}, Phys. Rev. Lett. \textbf{59}, 1092 (1987)] when strong field ionization is enhanced due to the transient population of excited states during the ionization, is revisited. An intuitive model is put forward which explains the mechanism of the intermediate population of excited states during nonadiabatic tunneling ionization via the under-the-barrier recollision and recombination. The theoretical model is based on perturbative strong-field approximation (SFA), where the sub-barrier bound-continuum-bound pathway is described in the second-order SFA, while the further ionization from the excited state by an additional perturbative step. The enhancement of ionization is shown to arise due to the constructive interference of contributions into the excitation amplitudes originating from different laser cycles. The applied model provides an intuitive understanding of the electron dynamics during a Freeman resonance in strong-field ionization, as well as means of enhancing the process and possible applications to related processes.

References in corpus (4)

• Tunneling dynamics in multiphoton ionization and attoclock calibration
• Muon pair creation by two x-ray laser photons in the field of an atomic nucleus
• Bound-free ${\mathbf{e}}^{+}{\mathbf{e}}^{-}$ pair creation with a linearly polarized laser field and a nuclear field
• Evidence of ac-Stark-shifted resonances in intense two-color circularly polarized laser fields