Laser-induced nonlinear excitation of collective electron motion in a cluster
Laser-induced nonlinear excitation of collective electron motion in a cluster
复制标题
激光诱导团簇中电子集体运动的非线性激发
DOI：
10.1088/0953-4075/36/18/310
复制
发表时间：
2003
期刊：
影响因子：
--
通讯作者：
W. Becker
中科院分区：
文献类型：
--
作者：
S. Fomichev;S. Popruzhenko;D. Zaretsky;W. Becker
我们考虑了一个大的集群内的非线性集体电子动力学照射一个强大的线性极化短（0.1？ps）激光脉冲。利用不可压缩介质近似，导出了强激光场驱动下电子云质心运动方程。这个方程的分析表明，奇次谐波的基本频率在集群的偶极矩的存在下，在内部和散射电场。中性和电离的集群被认为是。对于半径为R 100？？被飞秒钛金属辐射蓝宝石激光器的峰值强度为I 1016？什么？cm？2，三倍频基频附近的内部电场强度被证明是相同的数量级的基本领域。原因是，无论是金属和激光电离的货车范德华集群的米氏表面等离子体能量？M大约是5 eV，接近钛的三倍能量。蓝宝石激光场量子另一方面，与米氏频率的一阶共振的条件是不满足的存在期间的主激光脉冲，但只是暂时的，无论是在第一次发病的脉冲的前沿（货车德瓦尔斯集群）或在随后的库仑爆炸的内部电离。在这两种情况下，离子密度降低。强三次谐波的存在导致，特别是，以增强生产的多电荷离子在集群中照射的强激光场，与孤立的原子相比。这一点进行了讨论，根据最近的实验结果，生产的多电荷离子在激光？集群实验三次谐波产生的集群在一个强的激光场，作为集群和激光场参数的函数，也被认为是。
We consider the nonlinear collective electron dynamics inside a large cluster irradiated by a strong linearly polarized short (0.1 ?ps) laser pulse. The equation of the centre-of-mass motion of the electron cloud driven by the strong laser field is derived using the approximation of an incompressible medium. The analysis of this equation demonstrates the presence of odd harmonics of the fundamental frequency in the cluster dipole moment, and in both the internal and the scattered electric field. Both neutral and ionized clusters are considered. For clusters with radii R 100?? irradiated by a femtosecond titanium?sapphire laser with a peak intensity of I 1016?W?cm?2, the internal electric field strength near the tripled fundamental frequency is shown to be of the same order as the field of the fundamental. The reason is that both for metallic and for laser-ionized van der Waals clusters the Mie surface-plasmon energy ?M is around 5 eV, which is close to three times the energy of a titanium?sapphire laser-field quantum. On the other hand, the condition for first-order resonance with the Mie frequency is not met during the presence of the main laser pulse, but only temporarily, either at the first onset of inner ionization on the leading edge of the pulse (for van der Waals clusters) or during the subsequent Coulomb explosion. In both cases, the ion density is reduced. The presence of a strong third harmonic leads, in particular, to the enhanced production of multiply charged ions in clusters irradiated by a strong laser field, as compared with isolated atoms. This point is discussed in the light of recent experimental results on the production of multiply charged ions in laser?cluster experiments. Third-harmonic generation by a cluster in a strong laser field, as a function of both the cluster and the laser-field parameters, is also considered.