Frustrated tunnel ionization in the few-cycle regime*

Frustrated Tunnel Ionization (FTI) is a strong-field phenomenon where an ultrashort laser pulse excites a target atom, leaving it in a Rydberg state~[Nubbemeyer, T., et al. Phys. Rev. Lett. 101(23): 233001 (2008)]. This occurs after a tunneling ionization event when the dominant ionization channel is `frustrated' by the atomic Coulomb potential. Studying the mechanism behind FTI facilitates our understanding of atomic and molecular strong-field dynamics; e.g. FTI is observed in time-resolved ionization dynamics [Sabbar, M., et al. Nat. Phys. 13(5): 472-478 (2017)] and delayed ionization~[Larimian, S., et al. Phys. Rev. A 94(3) (2016)], and the fragmentation of molecules~[Manschwetus, B., et al. Phys. Rev. Lett. 102(11): 113002 (2009)]. Here we compare our experimental and theoretical FTI yields for few- and multi-cycle pulses. We find that for the same pulse energy more FTI is generated with few-cycle pulses.