Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO_2 laser bombardment on quartz sample

摘要

An experimental study on the pre-irradiation effect observed on quartz sample when TEA CO_2 laser pulse (550 mJ, 200 ns) was focused repeatedly at a fixed point of qurtz sample under surrounding gas of air at 2 torr was made. The disappearance of this effect at later stages was found to be connected with the appearance of a crater of appropriate depth created by repeated irradiation on the sample surface. Analysis of the experimental data imply that the pre-irradiation effect is due to the confinement of the fast electron and by the confinement of the electrons, laser absorption takes place effectively to induce localized hot plasma from which atoms can gush with supersonic speed. Hydrodynamic confinement also takes place after several tens of shots of the laser irradiation due to the geometrical focusing of gushed atoms flow in the crater with effective enhancement of the shock wave generation.