【作者】 黄云霞；

【导师】 杨晓华；

【作者基本信息】 华东师范大学 ， 光学， 2014， 博士

【摘要】 分子取向指的是分子轴在外场下沿着特定方向指向的行为。随着冷分子技术的发展,越来越多的研究者开始从事分子取向的研究,发展了多种取向分子的方法,如六极场取向、强力取向、复合场取向、激光场取向等。与各向同性的分子相比,取向后的分子对于研究分子化学反应动力学、摆动光谱、光电子成像等都具有重要意义。本文提出开关静电场取向具有较小转动常数分子的方法。由于静电场开关时间可以与分子转动周期相比拟,因此该方法可以实现分子的非绝热取向。非绝热作用导致的零场取向可以有效降低外场对取向分子后继研究的影响。其次,本文针对永久偶极矩较小的分子,提出了复合场取向的方法。这种复合场取向方法基于静电场与激光场的耦合,可以将激光场形成的分子排列转变为分子取向。即使较弱的静电场也能耦合激光场,产生较大的分子取向度。第三,研究了两种非高斯形状激光场对复合场取向的增强作用。采用缓慢上升快速下降的激光场可以使分子在脉冲最强处产生的最大取向值,在激光场关闭后周期性重现。而整形飞秒脉冲形成的缓慢上升脉冲串也可以有效增强复合场中分子的取向度。这种增强效果主要是由脉冲缓慢上升时特殊的上升沿引起的。第四,考虑到分子在复合场中相互作用势随着激光场和静电场强度的变化,本文提出将取向效应应用于分子Stark减速中,计算表明,该方法可以有效增强分子的减速效率。最后,本文对研究工作进行了总结和展望。更多还原

【Abstract】 Molecular orientation is the behavior that the molecular permanent dipole moment points to a specific direction in a laboratory frame when the molecules interact with external fields. With the development of molecular cooling, more and more researchers engaged in the study of the molecular orientation and proposed various methods, such as hexapole field state selector, brute force method, combined fields molecular orientation, and laser field techniques. Compared with isotropic molecules, oriented molecules are more important for the studies of the chemical reaction dynamics, pendular spectroscopy, photoelectron imaging and other relations.This thesis firstly proposes a method by switching an electrostatic field to orient molecules with small rotational constant. The nonadiabatic molecular orientation can be realized when the switching time of the electrostatic field is similar to the molecular rotational period, and the field-free molecular orientation can provide more opportunities for further applications. Secondly, the method of combined fields to orient molecules with small permanent dipole moment is proposed. This method is based on the coupling of the electrostatic and laser fields because the molecular alignment induced by the laser field can be converted to the molecular orientation, and even in a weak electrostatic field condition, a large degree of the molecular orientation can be obtained. Thirdly, the thesis studies the enhancement of two non-Gaussian laser fields to the molecular orientation combined with an electrostatic field. As to a slow turn-on and rapid turn-off laser field, the molecular orientation can obtain the maximal degree at the peak intensity of the laser pulse and reappeared periodically after the laser field turns off. The molecular orientation can also be enhanced by the cubic phase shaped femtosecond laser pulse in the combined fields, which is mainly due to the special rising edge of the shaped pulse. Finally, the molecular orientation of combined fields is applied in the molecular Stark deceleration. The preliminary analysis indicates that the linearly polarized laser field can enhance the efficiency of molecular deceleration obviously.A summary and an outlook of this work are stated at the end of this thesis.更多还原