High-order harmonic generation (HHG) creates coherent high-frequency radiation via the process of strong field ionization followed by recombination. Recently, a complementary approach based on frustrated tunnel ionization (FTI) was demonstrated [Yun et al., Nat. Photon. 12, 620 (2018)]. It uses spectrally separated peaks created by lower quantum number Rydberg states to produce coherent extreme ultraviolet (EUV) light. While much is understood about enhancing emission from HHG by controlling recombining electron trajectories, relatively little is known about controlling the quantum number distribution of Rydberg states. This distribution is generally believed to be determined primarily by field strength and laser frequency. We show that, in fact, it also changes significantly with the duration of the laser pulse: Increasing pulse duration depletes lower lying Rydberg states, thereby substantially decreasing EUV yield. Using electron trajectory analysis, we identify elastic recollision as the underlying cause. Our results open the door to greater control over production of coherent high-frequency radiation, by combining FTI and HHG mechanisms, and also improved the interpretation of molecular imaging experiments that rely on elastic electron recollision.

中文翻译：

---

通过激光脉冲持续时间控制里德堡态的量子数和光发射

高次谐波生成 (HHG) 通过强场电离和复合过程产生相干高频辐射。最近，展示了一种基于受挫隧道电离 (FTI) 的补充方法 [Yun等人。，纳特。光子。 12, 620 (2018)]。它使用由较低量子数里德堡态产生的光谱分离峰来产生相干的极紫外 (EUV) 光。虽然人们对通过控制复合电子轨迹来增强 HHG 的发射有很多了解，但对控制里德堡态的量子数分布知之甚少。通常认为这种分布主要由场强和激光频率决定。我们表明，事实上，它也随着激光脉冲的持续时间发生显着变化：增加脉冲持续时间会耗尽较低的里德堡态，从而显着降低 EUV 产率。使用电子轨迹分析，我们确定弹性碰撞是根本原因。我们的结果为更好地控制相干高频辐射的产生打开了大门，