Observation of dynamic Stark resonances in strong-field excitation
Observation of dynamic Stark resonances in strong-field excitation
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DOI：
10.1103/physreva.101.053402
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发表时间：
2019-12
影响因子：
2.9
通讯作者：
D. Chetty;R. Glover;B. deHarak;X. Tong;Han Xu;T. Pauly;Noah H. Smith;K. Hamilton;K. Bartschat;J. Ziegel;N. Douguet;A. Luiten;P. Light;I. Litvinyuk;R. Sang
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文献类型：
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作者：
D. Chetty;R. Glover;B. deHarak;X. Tong;Han Xu;T. Pauly;Noah H. Smith;K. Hamilton;K. Bartschat;J. Ziegel;N. Douguet;A. Luiten;P. Light;I. Litvinyuk;R. Sang
我们用超短近红外脉冲研究了氩气中的交流斯塔克位移共振。使用 30 fs 脉冲，我们观察到对应于 13 和 14 个光子吸收的强度区域中激发产率的周期性增强。通过仅用几个光学周期将脉冲持续时间减少到 6 fs，我们还证明增强效果显着降低，超出了实验中可测量的范围。将这些结果与与实验结果定量一致的数值预测进行比较，我们发现，尽管量子态分布可能很宽，但增强很大程度上是由于选定的几个 AC 斯塔克位移谐振态的有效布居，而不是电离通道的关闭。由于这些共振取决于激光场的频率和强度，因此 6 fs 脉冲的宽带宽意味着在很大的强度范围内满足共振条件。体积平均效应进一步夸大了这一点，导致几乎所有强度都激发 5g$ 状态，并降低了增强的明显幅度。对于 30 fs 脉冲，体积平均也拓宽了量子态分布，但增强效果仍然足够大，足以维持下去。在这种情况下，对单一状态的激发选择性会降低到相对总体的 25% 以下。然而，对与时间相关的薛定谔方程模拟的分析表明，如果可以消除体积平均并且可以精确控制强度，则高达 60% 的激发进入单一状态是可能的。
We investigate AC Stark-shifted resonances in argon with ultrashort near-infrared pulses. Using 30 fs pulses, we observe periodic enhancements of the excitation yield in the intensity regions corresponding to the absorption of 13 and 14 photons. By reducing the pulse duration to 6 fs with only a few optical cycles, we also demonstrate that the enhancements are significantly reduced beyond what is measurable in the experiment. Comparing these to numerical predictions, which are in quantitative agreement with experimental results, we find that even though the quantum state distribution can be broad, the enhancements are largely due to the efficient population of a select few AC Stark-shifted resonant states rather than the closing of an ionization channel. Because these resonances are dependent on the frequency and intensity of the laser field, the broad bandwidth of the 6 fs pulses means that the resonance condition is fulfilled across a large range of intensities. This is further exaggerated by volume-averaging effects, resulting in excitation of the $5g$ state at almost all intensities and reducing the apparent magnitude of the enhancements. For 30 fs pulses, volume averaging also broadens the quantum state distribution, but the enhancements are still large enough to survive. In this case, selectivity of excitation to a single state is reduced below 25% of the relative population. However, an analysis of time-dependent Schr\"odinger equation simulations indicates that excitation of up to 60% into a single state is possible if volume averaging can be eliminated and the intensity can be precisely controlled.