激光烧蚀Al靶产生的等离子体中辐射粒子的速度及激波

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200μm,靶面上功率密度分别为1.91×10¹⁰,5.10×10¹⁰和7.64×10¹⁰W/cm²时,测得辐射粒子Al的速度均在10⁶cm/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(shockwave model)较好地解释了实验结果,并得出激波的波面基本为柱对称 关键词： 激光等离子体 平面Al靶 粒子速度分布 激波

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

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(3p²P—4s²S), the velocity distribution of AlI in space has been determined at laser power densities of 1.91×10¹⁰, 5.10×10¹⁰ and 7.64×10¹⁰W/cm², respectively, when the ablating size is about 200 μm. The velocity is of the order of 10⁶ 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.