锰原子的二步多光子与三步三光子共振电离研究

2+1,1+1 and 1+1+1 Multiphoton Resonant Ionization of Manganese Atom

激光共振电离技术是痕量分析中的重要手段之一。文章以速率方程理论为基础，对锰原子的激光共振电离过程进行了分析，讨论了电离过程中各级激发光功率密度及激光作用时间对电离效率的影响；提出了根据所要求的电离效率和激光作用时间计算所需要的各激发光或电离激光的功率密度的方法；得到了饱和激发或饱和电离的规律及阈值条件。研究发现，在激光作用时间为10ns时，锰原子饱和电离的激光强度阈值基本都在10^8W·cm^-2的量级，只有“1＋1”双色双共振低三个量级；而“1＋1”和“1＋1＋1”饱和激发的激光强度阈值则在10^2～10^3W·cm^-2量级；并且随着激光作用时间的增加，各过程的饱和激发和饱和电离的激光强度阈值将单调减少。

Resonance ionization spectroscopy （RIS） is an important technique for trace analyses. In the present paper, based on the population rate equations, ＂2＋1＂, ＂1＋1＂ and ＂1＋1＋1＂ multiphoton resonant ionization processes of Mn atom are studied by computer simulation. The phenomena and the threshold condition of saturated excitation and ionization processes are discussed. The threshold laser intensities for saturated ionization of Mn atom with different RIS schemes are calculated. With the typical Q-switched laser duration of 10 ns, the obtained saturation threshold laser intensity for the ionization steps in all the resonant ionization processes of Mn is about 10^8 W·cm^-2 with the exception of the ＂1＋1＂ resonant ionization of Mn which is 3 orders of magnitude lower. The obtained threshold laser intensity for the saturated excitation steps is about 10^2-10^3 W·cm^-2 in ＂1＋1＂ and ＂1＋1＋1＂ ionization processes. It is also shown that the threshold laser intensity required for saturated excitation and ionization processes turns smaller with the laser duration prolonged.