Monday 13 October 2014
to 11:00 at
Tony Hansson (Molecular Physics Department)
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.