镧系原子激发态光电离动力学研究

镧系原子是4f内开壳层多电子体系，广泛应用于天体物理、光学、磁学、催化、冷原子物理、生物医药、激光材料和新能源技术等高新领域，这些领域研究迫切需求其能级、光谱和光电离截面信息，现有镧系原子激发态的能级和光电离数据非常缺乏。本项目拟采用激光泵浦-探测实验方案，在饱和共振激发情形下测量Ce、Pr、Nd、Sm、Gd、Lu等原子激发态阈限光电离截面、光电离截面的电离富余能依赖关系和极化效应，研究高激发态REMPI光谱和自电离共振，结合理论分析，揭示镧系原子激发态光电离机理。采用激光溅射和超声分子束产生低能电子态的自由原子，由可调谐染料激光激发基态原子制备激发态，另一束染料激光电离激发态原子或激发至自电离态，高灵敏TOF质谱检测离子产物，由离子产额和电离光子通量的关系获得激发态光电离截面。研究结果为改进的镧系原子理论研究方法提供检验，丰富4f原子激发态的光电离截面数据库。

Lanthanide metal atoms are multielectron systems with open 4f subshell and are found increasing uses in astrophysics, optics, magnetism, catalysis, ultracold atom physics, biomedicine, laser material, and new energy technology. All of these applications require extensive lanthanide atomic reference data that provide comprehensive and complete spectroscopy, energy levels, and photoionization cross sections. But the energy levels and photosissociation cross sections of the excited states of lanthanide atoms are rarely known. In this proposal, the threshold photoionization cross sections, dependence of the photoionization cross sections on the excess energy above the ionization threshold, and polarization effect of the photoionization cross section of the excited states of Ce, Pr, Nd, Sm, Gd, and Lu atoms et al will be investigated by the laser Pump-Probe scheme under the condition of saturated resonant excitation. In addition, the measurement of the REMPI spectrum and the autoionization resonance of the highly excited states will be carried out. These experimental investigations, combined with theoretical calculation, will reveal the photoionization dynamics of the excited states. The free atoms at low-lying excited states are produced using laser ablation combined with the supersonic molecular beam technique. The excited states of the atoms are populated by tunable dye laser radiaition and subsequently ionized by another tunable laser. The ions produced are detected by a TOF-MS spectrometer. The photoionization cross sections of the electronic states are finally obtained from the dependence of the ion yields on the ionization laser fluence. Our work will provide benchmark criterion on theoretical calculations and make significant contribution to the completeness of photoionization dynamic database of the excited states of the lanthanide atoms.