Generation of vacuum ultraviolet radiation as a result of an eighth-order nonlinearity in mercury vapor

An experimental investigation was made of direct generation of the eighth harmonic of neodymium laser radiation in mercury vapor. Estimates indicated that generation of an even (eighth) harmonic in a centrosymmetric medium was due to the appearance of a radial electric field as a result of free flight of photoelectrons from the region of constriction of the pump radiation.