Among different approaches to generate mirrorless lasing, resonant multiphoton pumping of gas constituents by deep-UV laser pulses exhibits so far the highest efficiency and produces measurable lasing energies, but the underlying mechanism was not yet fully settled. Here, we report lasing generation from atomic oxygen in a methane-air flame via femtosecond two-photon excitation. Temporal profiles of the lasing pulses were measured for varying concentrations of atomic oxygen, which shows that the peak intensity and time delay of the lasing pulse approximately scales as $N$ and $1/\sqrt{N}$, respectively, where $N$ represents the concentration. These scaling laws match well with the prediction of oscillatory superfluorescence (SF), indicating that the lasing we observed is essentially SF rather than amplified spontaneous emission. In addition, the quantum-beating effect was also observed in the time-resolved lasing pulse. A theoretical simulation based on nonadiabatic Maxwell-Bloch equations well reproduces the experimental observations of the temporal dynamics of the lasing pulses. These results on fundamentals should be beneficial for the better design and applications of lasing-based techniques.

中文翻译：

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飞秒激光诱导火焰中原子氧的量子拍频超荧光

在产生无反光镜激光的不同方法中，通过深紫外激光脉冲对气体成分进行共振多光子泵浦表现出迄今为止最高的效率并产生可测量的激光能量，但潜在的机制尚未完全确定。在这里，我们报告了通过飞秒双光子激发从甲烷-空气火焰中的原子氧产生激光。激光脉冲的时间分布是针对不同浓度的原子氧测量的，这表明激光脉冲的峰值强度和时间延迟大致按比例缩放$N$ 和 $1/\sqrt{N}$, 分别, 其中 $N$代表浓度。这些标度定律与振荡超荧光 (SF) 的预测非常吻合，表明我们观察到的激光本质上是 SF，而不是放大的自发发射。此外，在时间分辨激光脉冲中也观察到了量子拍频效应。基于非绝热麦克斯韦-布洛赫方程的理论模拟很好地再现了激光脉冲时间动力学的实验观察结果。这些基本原理的结果应该有利于更好地设计和应用基于激光的技术。