Shock wave plasma induced by TEA CO2 laser bombardment on glass samples at high pressures

An experimental study has been carried out on the dynamical process taking place in laser plasma, generated by TEA CO2 laser (400 mJ, 100 ns) irradiation on glass samples surrounding by air of high pressures up to 760 torr. Accurate dynamical characterization was performed by simultaneous observation of the plasma emission front and the shock wave front. The shock wave front was detected by a modified shadowgraph technique while the emission front was detected by observing the rising time at various slit positions. In spite of the occurrence of a new feature uncommon to laser plasma, generated in low air pressures, it is found that the two fronts coincide and move together at the initial stage of the laser plasma, but eventually separate from each other, with the emission front being left behind the shock wave front at a later stage. These characteristics hold for the atomic emission lines of all elements contained in the glass samples examined, regardless of their different atomic weights. It is therefore strongly indicative of the shock wave mechanism in the laser plasma generation and the emission in the high-pressure surrounding air.