Interference between nearly resonant three-photon excitation and third-harmonic generation probed by the cancellation of four-photon resonances.

Abstract

The destructive interference between the three-photon and the third-harmonic one-photon absorption in the vicinity of the 6s[3/2${]}_{1}$ state of Xe has been studied in the resonantly enhanced multiphoton ionization via nf states, through the cancellation of the nf, J=2 resonances of the spectrum, accessible by four-photon absorption. The gas-pressure, i.e., phase-matching, dependence of the three-photon detuning range from the 6s[3/2${]}_{1}$ state for which cancellation occurs has been investigated in one- and two-color experiments, including positive detuning from this state in positively dispersive regions. For obtaining cancellation, the theoretically predicted requirement of optically thick medium at the third-harmonic frequency is corroborated by present observations for negative detunings. The different cancellation behavior of the nf[3/2${]}_{2}$ and nf[5/2${]}_{2}$ states observed indicates the dependence of the effect on the atomic parameters of the coupled four-photon resonance. The experimental results are found to be in partial agreement with existing theoretical models.