Laser-Triggered Dynamic Breakdown of Gases and Laser-Induced Prebreakdown Signals

Dynamic breakdown of Ne and Ar gases biased to the pre- breakdown stage, with and without absorption of very short duration iucident N₂ laser pulses, is studied. Effects of bias and incident laser intensity are seen to be complementary. Laser illumination of the interelectrode gap causes gas breakdown at the cathode to take place at a faster rate and at lower breakdown threshold bias than without the illumination. Breakdown pulse shape varies according to gas composition and bias, and is much different from simple nonbreakdown “pre-breakdown” responses to the laser pulses. The prebrealidown signals are attributed to photon-enhanced ionization in the focal volume between the electrodes, while the laser-triggered breakdown pulses are attributed to photon-enhanced excitation and diffusion of such neutral atoms to the high field gradient region near the cathode, where cascade ionization collisional effects are amplified.