飞秒强激光脉冲与H原子团簇相互作用的库仑爆炸过程模拟

运用经典粒子动力学模拟方法，研究了飞秒强激光脉冲(10^15～10^16W／cm^2)与正二十面体构型氢原子团簇H13,H55，H147和H309的相互作用。通过模拟分析团簇的膨胀过程，发现团簇的膨胀是各向同性的，团簇的膨胀尺度R(t)／R(0)随团簇尺寸的增大而减小，即团簇尺寸愈大，与激光相互作用后膨胀碎解过程愈慢。研究结果表明，随着团簇中原子数目的增多，团簇库仑爆炸后所产生的离子的动能相应增大。由于正二十面体的对称壳层结构，离子动能分布具有尖峰结构。团簇库仑爆炸后离子的最大动能Emax与团簇库仑爆炸前的尺寸的平方成正比。且Emax随激光光强I增加而增大。但是当I增大到一定值Is时，Emax将出现饱和，这是因为I的增强已经不再改变团簇内原子的电离状态。随着团簇尺寸的增大，激光光强饱和值和离子能量将会继续提高。

3-D Simulations on Coulomb Explosions of Hydrogen Atomic Clusters Irradiated by an Intense Femtosecond Laser Pulse

Using classic particle dynamics simulations, the interaction process between an intense femtosecond laser pulse (1015～1016 W/cm2) and icosahedral hydrogen atomic clusters H13, H55, H147 and H309 has been studied. The expansion process of the clusters during and after laser irradiation has been examined, showing that the expansion of clusters is isotropic. The expansion scale R(t)/R(0) decreases with the increasing cluster size. This conclusion means that if the cluster size becomes larger, the process of expansion and explosion becomes slower. It is revealed that with an increase in the number of atoms in the cluster, the kinetic energy of ions generated in the Coulomb explosion of the ionized hydrogen clusters increases. Because of the symmetrical shell structure of the icosahedron, the distribution of the ionic kinetic energy features some pinnacles. It is also found that the calculated maximal kinetic energy Emax of the produced ions from Coulomb explosion of Hn clusters is roughly proportional to the square of the original cluster size. If laser intensity I increases, the maximal kinetic energy Emax of the produced ions also increases. But after I reaches a certain value Is, the maximal kinetic energy Emax of the produced ions no longer increases, i.e., it will be saturated. The reason is that the atoms in the cluster have been fully ionized, so the increase of laser intensity I doesn′t change the ionized state of the atoms in the cluster. It is concluded that with an increase in the cluster size, the kinetic energies of the produced ions and the laser saturation intensity increase too.