COHERENT VUV RADIATION BY HARMONIC CONVERSION OF MIXED FIELDS IN GASES

Harmonic generation in gases has been investigated by mixing of parall el-polarized fundamental (1064 nm) and second harmonic (532 nm) of a 1 00-mJ 35-ps Nd-YAG laser. The wave-mixing scheme generates even and od d harmonics whose conversion efficiency is enhanced by at least two or ders of magnitudes compared with single-frequency excitation. We have investigated the harmonic spectrum in Ar and N-2, up to the 14th harmo nics, versus the gas pressure and laser intensities for two different interaction lengths. Harmonic generation is barely affected by phase m ismatch in a large range of gas density variation, and for both config urations of active medium. Conversion efficiency of each harmonic vers us laser intensities decreases steeply near the saturation threshold o f ionization of selected gas.