Nonlinear properties of silica and air for picosecond ultraviolet pulses

The nonlinear power limiting processes in silica and air are investigated for picosecond pulses at the KrF wavelength. The two-photon absorption coefficient and the nonlinear refractive index in silica are measured to be 0.06cm / GW and 1.7 x 10-13 e.s.u. respectively. A mechanism for the rapid spectral broadening in air based on Raman-enhanced four-wave mixing is proposed. Experimental evidence supporting this hypothesis is presented