Laser beam induced breakdown in helium and argon

Abstract

Measurements of the laser radiation power density Pth required to cause ionization growth and breakdown in the pressure ranges 1800 less-than-or-eq, slant p less-than-or-eq, slant 16 000 torr and 200 less-than-or-eq, slant p less-than-or-eq, slant 20 000 torr have been made in helium and argon, respectively. Three Q-switched lasers (ruby, Nd, and dye) were used to investigate the dependence of Pth upon pressure, radiation frequency ω and flash duration 2τ. Values of Pth lie between 1011 W cm−2 at low pressures and 1010 W cm−2 at high pressures.