Growth of shielding in a laser plasma

An experimental investigation was made of the interaction between pulsed CO₂ laser radiation and the optical breakdown plasma generated by this radiation near the surfaces of glass, Duralumin, quartz, polymethylmethacrylate, and lithium fluoride samples. This radiation had durations of 2 and 10 μs and an energy density of between 1 and 40 J/cm² in a radiation spot of 3 cm² area. The plasma shielding of the laser radiation had a threshold at energy densities exceeding appreciably the energy threshold of plasma formation. In the range of laser pulse energies between these two thresholds the plasma remained transmitting for the laser radiation. The shielding energy thresholds were determined and it was found that the fraction of the laser pulse energy not transmitted by the plasma reached saturation at the 0.5–0.9 level, depending on the materials studied.