Spontaneous-Field-Induced Optical Second-Harmonic Generation in Atomic Vapors

Abstract
It is shown that optical second-harmonic generation is possible in dispersive atomic vapors since a static electric field is spontaneously created by the fundamental laser beam. When multiphoton ionization of atoms occurs simultaneously in the interaction, the spontaneous field and second-harmonic generation are significantly enhanced. Our experimental results for atomic sodium vapor irradiated by picosecond Nd-doped yttrium-aluminum-garnet laser pulses agree well with the theoretical predictions.