Laser-induced breakdown in nitrogen and the rare gases at 0.53 and 0.357μm

An experimental and theoretical investigation of laser-induced breakdown was carried out at 0.53 and 0.35 mu m for the following gases: N 2 , Ar, Ne and Xe. A Nd:YAG laser of 15 ns pulse duration was used in its second and third harmonics. The breakdown threshold intensity I th in the pressure range 0.2<p<15 atm was measured. I th at p=3 atm was found to be 10 12 (5*10 11 ), 8*10 10 (1*10 11 ), 5*10 11 (10 12 ) and 4*10 10 (2*10 10 ) W cm -2 for N 2 , Ar, Ne and Xe, respectively, at 0.53 mu m (0.35 mu m). The threshold is defined as the appearance of a visible flash and/or greater than 5% absorption of beam energy. The p -1 scaling of I th for Ne, Ar and Xe and p -0.6 scaling for N 2 indicates that the threshold is associated at both wavelengths with avalanche breakdown rather than multi-photon ionisation.