We studied the above-threshold ionization (ATI) spectra of argon in circularly polarized pulse by the atom-Volkov strong-field approximation (SFA). A dip appears in the spectra due to the presence of a zero in the dipole matrix element, corresponding to a transition from the ground state to the L = 2 continuum at electron kinetic energy ∼30.6 eV. No such dip appears when the time-dependent Schrödinger equation (TDSE) is used instead, because the transition amplitude in SFA is the first-order term in the S-matrix series while TDSE contains all orders. In contrast, the effect of Cooper minimum shows up in high-order harmonic generations, which is an inverse process of photoionization where the recombination transition is first-order. We examine several sets of pulse parameters and found that when the SFA validity conditions are satisfied, the atom-Volkov SFA generates better ATI spectra than the simple SFA.

中文翻译：

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用原子-沃尔科夫强场近似研究圆偏振脉冲中氩的光电子能谱

我们通过原子-沃尔科夫强场近似 (SFA) 研究了圆偏振脉冲中氩的超阈值电离 (ATI) 光谱。由于偶极子矩阵元素中存在零，光谱中出现下降，对应于从基态到大号= 2 连续谱，电子动能为 ∼30.6 eV。当改用瞬态薛定谔方程 (TDSE) 时，不会出现这种下降，因为 SFA 中的跃迁振幅是方程中的一阶项小号-矩阵系列，而 TDSE 包含所有订单。相反，库珀极小值的影响出现在高次谐波的产生中，这是光电离的逆过程，其中复合跃迁是一阶的。我们检查了几组脉冲参数，发现当满足 SFA 有效性条件时，atom-Volkov SFA 生成的 ATI 光谱比简单的 SFA 更好。