Detection of the Density Jump in the Laser-Induced Shock Wave Plasma Using Low Energy Nd:YAG Laser at Low Pressures of Air.

Abstract

A special interferometric technique with high sensitivity has been devised on the basis of rainbow refractometry for the detection of density jump signal withouthe use of an additional and delicate amplitude-splitting setup.This new technique was used for the characterization of shock wave plasma induced by a low energy of Q-sw Nd: YAG laser (14-64mJ) on zinc samples under reduced air pressure (3-30 Torr). An unmistakable signal of density jump was detected simultaneously with the observation of emission front signal, implying that the emission front and the front of the shock wave coincided and moved together with time at the initial stage of the secondary plasma expansion. The result of measurement also showed that at a later stage, the emission front began to separate from and left behind the blast wave front propagating in the surrounding gas. This result is a direct proof of our shock wave model to explain the excitation process of the laser-induced plasma.