Coherent dynamics of H− local modes in the alkaline earth fluorides

Two pulse infrared free induction decay (IR-FID) measurements performed on the substitutional local modes of H− ions in CaF2, SrF2 and BaF2 crystals are striking in that dramatic modulations (quantum beats) occur at negative delay times. We attribute this to interference between multiple vibrational levels via anharmonic ladder climbing and spectrally resolving the IR-FID signal allows unambiguous assignments of the participating vibrational states.