强激光场中分子双电离和解离的相关研究

【作者】 李燕；

【导师】 杨世平；

【作者基本信息】 河北师范大学 ， 理论物理， 2007， 硕士

【摘要】 本文应用修正的半经典再散射模型,研究了发生非次序双电离的双原子分子的离子的动量分布,以及发生双电离的两个电子的动量相关情况。发现由于双原子分子存在分子取向,在有外加电场时,外加电场将破坏分子原有的对称性,使得在外加场与分子轴的夹角成0度角和90度角时（即通常说的外加场与分子取向平行和垂直两种情况）,分子将显现出不同的双电离机制,具有不同的离子动量分布。通过用半经典再散射模型对双原子分子的双电离现象的研究,使得我们对非次序双电离的电离机制有了更好的理解。由于氢分子与氮分子它们的束缚电子的价电子轨道有类似的对称性,而且两种分子的核间距及电离能相近,因此用类氢模型模拟氮分子在定性上能够取得较好的结果。通过对氢分子双电离的模拟,从本质上揭示了非次序双电离的物理机制,发现了氢分子非次序双电离对于分子轴与外场夹角以及势垒的高度有着强烈的依赖关系;此外,同一种取向下的双电离对电场强度同样有一定的依赖。本文仅研究了两种极端情况（即分子的取向方向与外场成0度角和90度角）下的双电离问题,分子轴与外场成任意角度时的双电离情况将成为我们下一步工作的重点。最后,我们还应用半经典再散射模型对D₂的解离过程进行了模拟,获得的D2+的动能分布与实验相符;提出了一种新的解离图像:作用到分子上的激光场波长的不同,会使隧穿电子的返回动能不同,从而造成D₂解离机制的改变。更多还原

【Abstract】 Using a semiclassicial rescattering model, we investigate the electron correlation in non-sequential double ionization （NSDI） process of diatomic molecules, which are aligned parallel and perpendicular to the intense linearly polarized filed, achieving insight into the molecular NSDI dynamics.It is shown that a simple hydrogen-molecule-like model can simulate nitrogen molecule effectively and also give the electron momentum correlation qualitatively and quantitatively consistent with experimental result. This indicates that the symmetry of the valence orbital （bonding symmetry） dominates the NSDI process of diatomic molecule in the present of laser field. A simple semiclassical model based on electron recollision picture is capable to reproduce qualitatively the experimental findings and provide a clear picture to the NSDI dynamics, and explain the intrinsical mechanism of NSDI of diatomic molecules. Our analysis also indicates that the NSDI mechanism is dependent on the alignment due to the dependence of the potential barrier on the alignment. Moreover, the shapes of the momentum distributions have close dependence on the laser intensity. Further work of arbitrary alignment molecular ensemble is under work.It is shown that in the non-sequential double ionization of D₂, as the laser varies from short to long wavelength, the returning electron’s kinetic energy varies from below to above the ionization threshold of the parent ion, resulting in the dominance of collisional ionization at shorter laser wavelength and field-ionization at longer laser wavelength. We also calculate the double ionization time distribution of D2 and kinetic energy distribution of D+. The theoretical results are qualitatively consistent with the experimental measurements.更多还原