Competition between two-photon-resonant three-photon ionization and four-wave mixing in Xe

Abstract

Competitive inhibition of a resonance enhanced multiphoton ionization process by a resonant four-wave mixing has been observed in Xe atoms. When an intense IR (1064 nm) laser was applied to a sample of Xe which was also being irradiated by a UV laser tuned to the two-photon absorption line of Xe, the two-photon-resonant three-photon ionization signals decreased with increasing IR laser power. This phenomenon is dependent on the resonant states of Xe and the polarization of the two laser beams. Three 6$s$ excited states [5/2]${}_{2}$, [3/2]${}_{2}$, and [1/2]${}_{0}$ were examined. At the [1/2]${}_{0}$ resonant state, the ion signals were not decreased but slightly increased with the increase of the IR laser power. No suppression of the ion signal was observed at the [5/2]${}_{2}$ resonant state, when the polarization directions of the lasers were perpendicular to each other. The result of the polarization dependence reflects the selection rules of four-wave mixing. A simple rate equation analysis including the contribution of two-photon ionization from the [1/2]${}_{0}$ state by the IR laser well represents the IR laser-power dependence of the ion signal.