Coherent population trapping involving Rydberg states in xenon probed by ionization suppression
Fachbereich Physik der Universität, Universität Kaiserslautern, 67663 Kaiserslautern, Germany
Corresponding author: a email@example.com
Revised: 25 June 2001
Published online: 15 October 2001
We report the observation of pronounced coherent population trapping and dark resonances in Rydberg states of xenon. A weak two-photon coupling with radiation of nm is induced between the ground state of xenon and state , leading to (2+1) resonantly enhanced three-photon ionization. The state is strongly coupled by radiation with nm to or Rydberg states with principal quantum numbers n in the range and with the rotational quantum number of the ionic core or . The ionization is monitored through observation of the photoelectrons with an energy resolution meV which is sufficient to distinguish the ionization processes into the two ionization continua. Pronounced and robust dark resonances are observed in the ionization rate whenever is tuned to resonance with one of the ns- or nd-Rydberg states. The dark resonances are due to efficient population trapping in the atomic ground state through the suppression of excitation of the intermediate state . The resolution is sufficient to resolve the hyperfine structure of the ns-Rydberg levels for odd xenon isotopes. The hyperfine splitting does not vary significantly with n in the given range. Results from model calculations taking the natural isotope abundance into account are in good agreement with the observed spectral structures. Pronounced dark resonances are also observed when the dressing radiation field with is generated from a laser with poor coherence properties. The maximum reduction of the ionization signal clearly exceeds 50% , a value which is expected to be the maximum, when the dip is caused by saturation of the transition rate between the intermediate and the Rydberg state due to incoherent radiation. This work demonstrates the potential of dark resonance spectroscopy of high lying electronic states of rare gas atoms.
PACS: 42.50.Hz – Strong-field excitation of optical transitions in quantum systems; multi-photon processes; dynamic Stark shift / 32.80.Rm – Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) / 32.10.Fn – Fine and hyperfine structure
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001