Studies of multiphoton production of vacuum-ultraviolet radiation in the rare gases

Measurements of the vacuum-ultraviolet (<80-nm) radiation produced by intense ultraviolet (248-nm) irradiation(1015-1016 W/cm2) of rare gases have revealed the copious presence of both harmonic radiation and fluorescencefrom excited levels. The highest harmonic observed was the seventeenth (14.6 nm) in Ne, the shortest wavelengthever produced by that means. Strong fluorescence was seen from ions of Ar, Kr, and Xe, with the shortestwavelengths observed being below 12 nm. Furthermore, radiation from inner-shell excited configurations in Xe, specifically the 4d95s5p ˜ 4d105s manifold of Xe7+ at ˜17.7 nm, was detected. These experimental findings, inalliance with other studies concerning multielectron processes, give evidence for a role of electron correlations in adirect nonlinear process of inner-shell excitation. © 1987, Optical Society of America.