Jakub Benda, Zdeněk Mašín, Sreelakshmi Palakkal, Franck Lépine, Saikat Nandi, Vincent Loriot
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引用次数: 0
摘要
在光电子能量通常超过 10 eV 的情况下,阿秒电离时间延迟通常使用所谓的渐近近似法来解释,即原子或分子延迟与普遍激光诱导贡献的总和。在这里,我们采用了双谐波 RABITT(通过双光子转换的干涉重建阿特秒拍动)配置来分离多光子途径,并测量电离时间延迟与敷料场强度的函数关系。我们证明了渐近理论的有效性可以扩展到阈值或更高阶的贡献,方法是将连续-连续转变的角动量依赖性严格地处理为普遍且易于计算的部分波特定修正因子。我们的渐近处理也适用于高阶干涉振幅,同时大大简化了它们的评估,并提供了透明的物理解释。通过与宽能量范围内的 ab initio 计算进行比较,证实了该方法对于共振附近的原子和分子目标、电离阈值以及发射积分信号和角分辨信号的有效性。
Angular momentum dependence in multiphoton ionization and attosecond time delays
Attosecond ionization time-delays at photoelectron energies above typically
10 eV are usually interpreted using the so called asymptotic approximation as a
sum of the atomic or molecular delays with a universal laser-induced
contribution. Here, we employ a two-harmonic RABITT (Reconstruction of
Attosecond Beating by Interference of Two-photon Transitions) configuration to
isolate the multiphoton pathways and measure the ionization time delays as a
function of the dressing field intensity. We show that the validity of the
asymptotic theory can be extended to the threshold or to higher-order
contributions by rigorously treating the angular-momentum dependence of the
continuum-continuum transitions into universal and easily computable
partial-wave-specific correction factors. Our asymptotic treatment is also
valid for higher-order interfering amplitudes while significantly simplifying
their evaluation and providing a transparent physical interpretation. The
validity of the method for atomic and molecular targets in the vicinity of
resonances, ionization thresholds, and for both the emission-integrated and
angularly resolved signal is confirmed by comparison to ab initio calculations
over a wide energy range.