OBSERVATION OF PARAMETRIC AMPLIFICATION WITH A FEMTOSECOND VACUUM-ULTRAVIOLET 4-WAVE DIFFERENCE-FREQUENCY MIXING SOURCE

The high conversion efficiency of the Xe-atom four-wave difference-frequency mixing (omega(3) = 2 omega(1) - omega(2)) vacuum UV (VUV) femtosecond source relies on a coincidental near two-photon resonance occurring when the omega(1) light pulses are at similar or equal to 248.5 nm. It also depends on the coherence properties of the input pulses. As in previous studies of this system, high-intensity femtosecond light pulses at omega(1) were produced by amplification in a KrF-excimer discharge, but the required 248.5-nm seed pulses were obtained from a new source based on near-threshold continuum generation. Nonlinear mixing in Xe of the pulses prepared at omega(1) with femtosecond visible light pulses of omega(2) yielded omega(2) --> omega(3) energy conversions of similar to 1 and VUV pulse energies as high as 60 mu J. At low input energies the beam at omega(2) was observed to be parametrically amplified by a factor similar or equal to 150.