Hüter O, Temps F
Institute of Physical Chemistry, Christian-Albrechts-University Kiel, Olshausenstr. 40, 24098 Kiel, Germany.
Rev Sci Instrum. 2017 Apr;88(4):046101. doi: 10.1063/1.4979799.
Femtosecond photoelectron imaging spectroscopy is a powerful technique for following state-resolved molecular transformations in complex coupled potential energy landscapes. To avoid unwanted nonlinear side-effects, the employed laser pulse energies are usually reduced to minimal values. However, the energy calibration of the photoelectron imaging detector is ideally performed using multi-photon above-threshold ionization of suitable atomic species, for which rather high laser intensities are required. In this work, we show that the calibration spectra of xenon obtained with high laser pulse energies cannot be directly used for the evaluation of molecular photoelectron spectra recorded using low-energy laser pulses. The reason is the intensity-dependent AC Stark shift of the atomic ionization energies to larger values, which in turn leads to a corresponding decrease of the photoelectron kinetic energies. We present a simple procedure to quantify this so-called ponderomotive shift and calculate the theoretically expected un-shifted photoelectron energies.
飞秒光电子成像光谱技术是一种用于追踪复杂耦合势能面中态分辨分子转变的强大技术。为避免不必要的非线性副作用，所使用的激光脉冲能量通常会降低到最小值。然而，光电子成像探测器的能量校准理想情况下是使用合适原子物种的多光子阈上电离来进行的，而这需要相当高的激光强度。在这项工作中，我们表明，用高激光脉冲能量获得的氙校准光谱不能直接用于评估使用低能量激光脉冲记录的分子光电子光谱。原因是原子电离能的强度依赖交流斯塔克位移会使其值增大，进而导致光电子动能相应降低。我们提出了一个简单的程序来量化这种所谓的有质动力位移，并计算理论上预期的未位移光电子能量。
