LASER-INDUCED BREAKDOWN IN NITROGEN AND THE RARE-GASES AT 0.53 AND 0.35 MU-M

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**t**h in the pressure range 0. 2 less than p less than 15 atm was measured. I**t**h at p equals 3 atm was found to be 10**1**2(5 multiplied by 10**1**1), 8 multiplied by 10**1**0(1 multiplied by 10**1**1), 5 multiplied by 10**1**1(10**1**2) and 4 multiplied by 10**1**0(2 multiplied by 10**1**0)W cm** minus **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** minus **1 scaling of I**t**h for Ne, Ar and Xe and p** minus **0**. **6 scaling for N//2 indicates that the threshold is associated at both wavelengths with avalanche breakdown rather than multi-photon ionization.