The high conversion efficiency of the Xe-atom four-wave difference-frequency mixing (ω3 = 2ω1 − ω2) vacuum UV (VIJV) femtosecond source relies on a coincidental near two-photon resonance occurring when the ω1 light pulses are at ≃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 ω1 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 ω1 with femtosecond visible light pulses of ω2 yielded ω2 → ω3 energy conversions of ~1 and VUV pulse energies as high as 60 μJ. At low input energies the beam at ω2 was observed to be parametrically amplified by a factor ≃150.
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Glownia et al. (1994) studied this question.