Electron dynamics from low-order harmonics generated by short laser pulses
Electron dynamics from low-order harmonics generated by short laser pulses
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短激光脉冲产生的低次谐波的电子动力学
DOI：
10.1103/physreva.96.023421
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发表时间：
2017-08
影响因子：
2.9
通讯作者：
Peng Liang-You
中科院分区：
文献类型：
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作者：
Xiong Wei-Hao;Gong Qihuang;Peng Liang-You
近年来，低次谐波作为高重复频率的相干光源得到了广泛的关注。此外，产生过程与束缚电子高度相关，因此可以应用于检测这些电子的动态。在这项工作中，我们从理论上研究了由单周期光脉冲产生的第一激发态以下的低阶谐波。我们数值求解三维含时薛定谔方程（TDSE）来计算谐波谱.借助于微扰模型，我们可以透明地理解光谱的产生过程。结果表明，驱动场的频率分量对谐波谱有敏感的影响。我们发现，载波包络相位（CEP）的低次谐波产生的依赖性来源于不同的谐波阶数的干扰。对于这些谐波，CEP效应只能在驱动激光的光谱非常宽时观察到，这对应于非常短的驱动脉冲。从依赖于CEP的干涉结构中，可以提取三次谐波和五次谐波的相位关系。所提取的信息指示原子响应引起所发射的低阶谐波的正啁啾。此外，我们研究了谐波相位计算的TDSE结果。谐波相位与绝热模型预测的相位不同，并且这种相位差可以与电子响应的时间延迟有关。我们从谐波相位中提取了时间延迟，并探讨了该时间延迟的CEP和强度依赖性。
Recently, low-order harmonics have gained much attention due to their applications as coherent light sources with a high repetition rate. In addition, the generation process is highly related to the bound electrons and can thus be applied to detect the dynamics of these electrons. In this work, we theoretically investigate the low-order harmonics below the first excited state, produced by a single-cycle optical pulse. We numerically solve the three-dimensional time-dependent Schr\"odinger equation (TDSE) to calculate the harmonic spectrum. With the help of a perturbation model, we can transparently understand the generation process of the spectrum. The results indicate that the harmonic spectrum can be sensitively influenced by the frequency component of the driving field. We find that the carrier envelope phase (CEP) dependence of low-order-harmonic generation originates from the interference of different harmonic orders. For these harmonics, the CEP effects can only be observed when the spectrum of the driving laser is extremely wide, which corresponds to the very short driving pulse. From the CEP-dependent interference structure, the phase relation of the third and the fifth harmonic can be extracted. The extracted information indicates that the atomic response induces a positive chirp for the emitted low-order harmonics. In addition, we investigated the harmonic phase calculated from the TDSE results. The harmonic phase is different from the phase predicted by the adiabatic model, and this phase difference can be related to the time delay of the electronic response. We extract the time delay from the harmonic phase and explore the CEP and intensity dependence of this time delay.