激光烧蚀Al靶产生的等离子体中辐射粒子的速度及激波

VELOCITY OF EMISSION PARTICLES AND SHOCKWAVE PRODUCED BY LASER-ABLATED Al TARGET *

在低真空条件下 (5Pa) ,通过测量脉冲激光烧蚀平面Al靶产生的等离子体辐射谱的时间分辨特征 ,得到辐射粒子速度的空间分布 .在激光脉冲宽度为 10ns,烧蚀斑直径为 2 0 0 μm ,靶面上功率密度分别为 1.91× 10 1 0 ,5 .10×10 1 0 和 7.6 4× 10 1 0 W cm2 时 ,测得辐射粒子Al的速度均在 10 6 cm s量级 ,且随着靶面径向距离的增大而近似呈指数衰减 .在距靶面的相同距离处 ,激光功率密度的增大反而使速度减小 .利用激波模型 (shockwavemodel)较好地解释了实验结果 。

Under low vacuum condition (5Pa), Q-switched YAG laser ablates plane aluminum target and plasma are produced. Optical emission spectroscopy is used to carry out time-resolved analysis of atomic particles. Using the resonance transition of AlI 396.1 nm(3p(2)P-4s(2)S), the velocity distribution of All in space has been determined at laser power densities of 1.91 X 10(10) 5.10 X 10(10) and 7.64 X 10(10) W/cm(2), respectively, when the ablating size is about 200 mum. The velocity is of the order of 10(6) cm/s and the time decays nearly agree with the exponential law as the radial distance from the target surface increases. At a fixed position, the velocity shows some decrease as the laser power density being increased, but when the distance is above 15 mm, the velocity converges to unification one. Shockwave model is used and gives a good agreement with the experimental results. From the model, it is deduced that the shockwave front has cylindrical symmetry.