Spectral phase matching for highly efficient frequency tripling of short-pulse KrF laser radiation in argon

For the efficient frequency tripling of KrF laser radiation, argon is very well suited as a nonlinear medium since a near-three-photon resonance can be used, which enhances the nonlinear susceptibility. According to theoretical predictions a zero crossing of the dispersive phase mismatch for the frequency-tripling process allows nearly perfect phase matching at high densities for the central KrF laser wavelength at 248.5 nm. Experiments that demonstrate the associated spectral sensitivity of the phase matching were performed in a pulsed argon gas jet for controlled input spectra and by varying the particle density up to 6×1018 cm-3. The experiments show good agreement with corresponding theoretical model calculations and explain the recently achieved high conversion efficiencies in frequency tripling of short-pulse KrF laser radiation.