Laser Induced Breakdown in High Pressure Noble Gases.

Abstract : Laser induced breakdown is studied both experimentally and analytically in high pressure helium, neon, and argon gases. It is shown that an analysis based on balancing electron production against electron loss yields good agreement with experimental data for the gases studied. Experimentally a giant-pulse ruby laser was used for the pressure range from ten atmospheres to two thousand atmospheres. The model used in the analysis assumes that laser photons are absorbed by the process of inverse bremsstrahlung. Free electrons are produced by collisional ionization and from photoionization and associative ionization of excited neutrals. The data taken indicates a minimum in the plot of threshold field versus pressure for helium and argon and a possible minimum beyond the pressure system limits for neon. In the comparison of experimental data to theoretical calculations, non-ideal behavior of the gas and the change in index of refraction with gas pressure are taken into account. (Author)