Generation of vacuum ultraviolet radiation in mercury vapor utilizing seventh- and ninth-order nonlinearities

The results are given of theoretical and experimental investigations of the generation of vacuum ultraviolet radiation by parametric frequency mixing of radiation from a neodymium laser using higher nonlinearities of a mercury vapor. The effects of interference of nonlinear polarizations of the seventh nonresonant and ninth resonant orders are reported. Investigations of the frequency dependence of the breakdown threshold (which is the main limiting factor) make it possible to relate the reduction in the threshold to a change from ten- to nine-photon ionization.