First Experimental Evidence of Destructive Interference Effects in Two-Photon Ionization of Cs Atoms

This Letter presents the first experimental evidence of destructive interference effects in multiphoton ionization. The experiment involves a Cs atomic beam crossed with a linearly polarized dye-laser beam whose intensity reaches 20 GW/${\mathrm{cm}}^2$ in the 460-540-nm wavelength range. As predicted by second-order perturbation theory, the generalized ionization cross section exhibits a deep minimum which is found to equal (9±5)×${10}^{-52\mathrm{}}$ ${\mathrm{cm}}^4$ s at 480 nm. Discrepancies with previous experiments are tentatively explained.