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Molecular Physics seminar

Resonances in intense field photoionization of O2

by Tony Hansson (SU Fysikum)

FB 55 ()

FB 55

We investigated by electron spectroscopy the strong-field multiphoton ionization (MPI) of O2 molecules with ultrashort laser pulses in the intensity range between the multiphoton ionization and tunneling regimes. The ionization proceeds by at least three different mechanisms, in addition to the eight- and nine-photon nonresonant pathways. Transient multiphoton resonances with vibrational Rydberg levels give rise to Freeman-type resonances, while some actually populated resonance levels yield extremely narrow lines by postpulse vibrational autoionization. When the lowest photon order resonance channel for the Rydberg states is closed, a third contribution becomes dominant with a main peak at 0.4 eV that appears to be similar to the in recent years discovered universal low-energy structure in the electron spectra of atoms and molecules [C. I. Blaga et al., Nat. Phys. 5, 335 (2009); W. Quan et al., Phys. Rev. Lett. 103, 093001 (2009)]. In this talk, I will review these results in the light of recent measurements with varied light polarization and with particular emphasis on the occurrence of resonances.