Nonlinear optical processes in xenon and krypton studied by two-color multiphoton ionization

Multiphoton ionization (MPI) and third-harmonic generation (THG) in xenon and krypton have been studied via three-photon resonance with the xenon 6s’ ${[1/2]}_1^0$ and krypton 5s${\left[\right(3/2\mathrm{}]}_1^0$ states. A second, tunable dye laser is used to couple these states to higher-lying even-parity states. Observations are reported regarding the third-harmonic related cancellation of the intermediate s-state population and the mechanisms of population of the final states. Effects of the four-photon resonance on THG are detailed. Changes induced by the second laser reduce THG in normally favorable regions and enable it in otherwise forbidden regions. Striking effects in the MPI spectra due to the changes induced in THG are reported.