Characterization of laser-produced aluminum plasma in ambient atmosphere of nitrogen using fast photography

摘要

We report on the pulsed-laser ablation of aluminum in ambient pressure of nitrogen varying from 0.01 to 70 Torr using images of the expanding plasma plume. At pressures ≥1 Torr plasma-gas interface showed severe distortion in the front of the expanding plume. The plasma expansion velocity showed oscillatory behavior with delay time beyond 260 ns and is attributed to Rayleigh-Taylor instability. The effect of background gas on inducing polarization in the ablated plasma is also reported. At low pressure of 0.1 Torr the degree of polarization of Al III transition 4s ~(2)S_(1/2)-4p ~(2)P_(3/2)~(0) at 569.6 nm increased with delay time. At pressures ≥1 Torr it showed an oscillatory behavior. The observed steep pressure gradient at the plasma-gas interface may result in strong self-generated magnetic field due to Rayleigh-Taylor instability.