Pressure-Induced Extra Resonances in Four-Wave Mixing: Evidence for a Breakdown of the Impact Approximation

Abstract

Experiments on pressure-induced extra resonances in degenerate four-wave mixing involving Zeeman coherence have been performed on Ba atoms in an argon atmosphere under conditions of large detunings from the Ba resonance line. The dependence on the detuning gives evidence for a breakdown of the impact approximation, when the laser is detuned by more than 5\ifmmode\times\else\texttimes\fi{}${10}^{11}$ rad ${\mathrm{sec}}^{\ensuremath{-}1}$; the behavior can be interpreted semiquantitatively by a model based on optical collisions.