Recent studies have demonstrated that in a few-cycle laser pulse, a coherent Rydberg atom—an atom in a superposition of the ground and highly excited states—can generate high-order harmonic generation (HHG) spectra with high conversion efficiency and high cutoff energy, making it a potential procedure for producing attosecond pulses. In this study, we theoretically report two interesting findings that can be realized experimentally: the nontrivial dependence of HHG cutoff on the laser carrier-envelope phase (CEP) and the double-plateau structure in the spectrum when the CEP ranges from 75° to 120°. The second effect has not been reported for a Rydberg atom in the previous studies focusing only on CEP of 0°. Finally, using classical simulation and time-frequency analysis, we explain the influence of the CEP on the cutoff energy and, especially, the origin of the double-plateau structure. Unlike the first plateau generated by the recombination of an electron escaping from the Rydberg state but returning to the ground state, the second one arises from the ionization from the ground state. Consequently, by controlling the laser CEP, the electron dynamics can be embedded in the structure of plateaus in the HHG spectra.

中文翻译：

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双平台结构和载流子包络相对几周期激光脉冲中里德堡原子产生高次谐波的影响

最近的研究表明，在几个周期的激光脉冲中，相干的里德堡原子（基态和高激发态的叠加原子）可以产生具有高转换效率和高截止能量的高次谐波产生（HHG）光谱，使其成为产生阿秒脉冲的潜在程序。在这项研究中，我们从理论上报告了两个有趣的发现，这些发现可以通过实验实现：当CEP范围为75°至120时，HHG截止值对激光载流子包络相（CEP）的非平凡依赖以及光谱中的双平稳结构°。在先前的研究中，仅集中于0°CEP尚未报道Rydberg原子的第二种效应。最后，使用经典模拟和时频分析，我们解释了CEP对截止能量的影响，特别是，双高原结构的起源。与通过从里德堡态逃逸但返回基态的电子复合产生的第一个平稳区不同，第二个平稳区是由从基态发生的电离产生的。因此，通过控制激光CEP，可以将电子动力学嵌入到HHG光谱的高原结构中。