GENERATION OF FEMTOSECOND VACUUM-ULTRAVIOLET PULSES

High power femtosecond pulses in the Vacuum Ultra Violet (VUV) have be en generated through the nonlinear interaction of femtosecond KrF puls es with xenon and argon gas. Under near resonant two photon excitation of xenon by a femtosecond KrF laser, parametric four wave mixing proc esses lead to VUV pulses at 147 and 108 nm with pulse energies in the 10 mu J range. Tuning is demonstrated by mixing the KrF pulse with a 5 00 fs dye laser pulse at 497 nm, resulting in 165 nm emission. In argo n, a three photon resonance leads to third harmonic generation at 83 n m and micro joule level pulses near 127 nm generated by a six wave mix ing process. Since the spectra of the VUV pulses show an ionization-in duced blue shift with increasing KrF laser intensity, the VUV pulses c an be shown to have temporal duration less than the pulse width (450 f s) of the KrF laser. Blue shifting of the third harmonic of the KrF la ser in argon is dominated by a reduction in the neutral gas density ra ther than by an increase in the electron density.