CANCELLATION EFFECTS IN 4-PHOTON-RESONANT 5-PHOTON IONIZATION THROUGH THE NF J=2 STATES OF XE

Partial cancellation of the ionization signal in the four-photon-resonant five-photon ionization via J = 2 4f and 5f resonances in Xe has been observed at increased gas pressures. Experiments with one and two counterpropagating laser beams provide strong evidence that cancellation is due to destructive interference at the three-photon step between the coherent three- and one-photon excitation channels, the latter involving one vacuum ultraviolet photon of the third-harmonic generation that occurs above the 6s[3/2]1o state. The well-known destructive interference for the ''on-resonance'' case is now shown to occur also for large detuning from the resonance (up to 2000 cm-1) probed by four-photon-resonant five-photon ionization. This type of cancellation may provide new insight in interference effects involved in multiphoton-excitation processes.