异核双原子和三原子分子在红外强激光场中的电离抑制

Ionization Suppression of Heteronuclear Diatomic and Triatomic Molecules in Strong Infrared Laser Fields

本文中，用飞行时间质谱研究了CO和C02分子在50fs、800nm激光场中的强场单电离和双电离现象，光强范围为2×10 13-2×10 14W／cm2．通过将分子与具有相同电离限的同伴原子Kr对比，我们研究了分子的电子结构对强场电离的影响．结果表明，两种分子的单电离和C0的双电离与原子Kr相比都没有明显的抑制，而CO2的双电离几率与Kr相比明显被抑制．据此实验现象并结合先前同核双原子分子（N2和O2）的研究结果，本文讨论了分子电离中不同抑制效应的机制．分析表明，CO和CO2分子不同的最高占据轨道使得其隧穿电子的角分布和波包问的双中心干涉完全不同。

Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide （CO） and carbon dioxide （CO2） in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×10 13 W/cm2 to 2×10 14 W/cm2 using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton （Kr）, which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization （NSDI） of CO, while the NSDI probability of CO2 is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules （N2 and O2）, the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO2 leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization.