Five-photon ionization of Na atoms in radiation fields of single-mode and multimode lasers

Measurements were made of the probability of direct five-photon ionization of Na atoms (adiabaticity parameter γ ~ 100) by multimode (N ~ 10⁴ modes) and single-mode neodymium laser radiation. For a given average radiation intensity the ionization probability was 110 ± 30 times greater in a multimode field than a single-mode field. Within the limits of the experimental error, this ratio agreed well with the theoretical value of the correlation function G = 120.