碱金属原子的光激发与光电离

Photoexcitation and photoionization of alkali atoms

本文研究了碱金属原子在三步激光脉冲作用下的光激发和光电离过程的动力学特性,重点关注和比较了锂和铯原子的异同.针对多种激发模式,本文不但建立了其原子布居数在各个跃迁态的速率方程组,还给出了各相关态的光激发和光电离过程的解析解.通过精心设计并选择了特殊情况,显著简化了解析解的数学表达式,从而凸显和讨论了其物理内涵.通过自行编程,系统地计算和观察了各种激发模式对锂原子的光激发和光电离过程的可能影响,研究和讨论了电离率随激光参数的变化规律.在相同激发模式下,比较和分析了采用两种不同激发路径所导致的各态原子布居率的变化,凸显了改变原子参数所产生的作用.探讨了锂和铯原子在类似的激发条件下在电离率方面的差别.最后,基于本文的研究结果,本文指出了优化电离率的多种途径.

The dynamical process of photoexcitation and photoionization of alkali atoms is studied with three-step laser pulses, focusing on the similarities and differences between Li and Cs atoms on their properties by making a comparison of them. Based on several excitation schemes, the present work not only establishes the rate equations of atom population for all related transition states, but also obtains the analytical solutions of photoexcitation and photoionization process. The mathematical solutions are simplified significantly by restricting the most general case to the several special cases, either designed or selected carefully, in order to highlight the main factors and obtain the physical insight underlying the complicated mathematical expressions. With self-programming, the possible impact of time configuration of laser pulses on the three-step laser excitation process of the photoexcitation and photoionization is calculated and studied systematically. Variation of the ionization e？ciency with the laser parameters is investigated and discussed. With the same time configuration of laser pulses, the dependences of atom population for all the related transition states on the two different excitation paths are compared and analyzed, reflecting the impact of changing the atomic parameters. Under the similar excitation conditions, the differences of ionization e？ciency between Li and Cs atoms are explored. Finally, based on the present study, several means for optimizing ionization e？ciency are proposed.