Book Description

Possible mechanisms responsible for laser-induced breakdown in super-high pressure gases are investigated both theoretically and experimentally. It is shown that the breakdown mechanism involves energy gain of free electrons by acceleration in the incident electromagnetic field while undergoing collisions with neutrals, and subsequent electron-impact ionization. This mechanism is described by classical microwave breakdown theory and favorably compares with the experimental measurements. Experimental breakdown threshold data in He, Ar, H2, and N2 was obtained over the pressure range 100-30,000 psi. Plasmas are produced in He, Ar, H2, and N2 over the pressure range 100-30,000 psi. The radiation from a giant-pulse ruby laser is focused within a pressure cell having three quartz windows and capable of withstanding 60,000 psi. Breakdown threshold data is taken for comparison with theory. Kerr cell photographs of the focal region provide time resolution of the macroscopic growth of the plasma. Two possible mechanisms are evaluated: multiquantum absorption and electron-impact ionization. The latter is analyzed both quantum mechanically by the inverse Bremsstrahlung theory and classically by microwave theory.