Zhang An, Liang Qingqing, Lei Mingwei, Yuan Luqi, Liu Yi, Fan Zhengquan, Zhang Xiang, Zhuang Songlin, Wu Chengyin, Gong Qihuang, Jiang Hongbing
Opt Express. 2019 Apr 29;27(9):12638-12646. doi: 10.1364/OE.27.012638.
Singly ionized nitrogen molecules in ambient air pumped by 800 nm femtosecond laser give rise to superradiant emission. Here, we study this superradiance by injecting a pair of resonant seeding pulses at different intensity ratios inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiant emission with a period of 1.3 fs is observed when the delay between the two seeding pulses is finely tuned. The modulation contrast is increased and then decreased with the delay time when the second seed pulse is stronger than the first one, and the maximum modulation contrast occurs at longer delay time when the second seeding pulse is stronger. This reveals the increase of the macroscopic polarization with time after the seeding pulse. Moreover, these observations provide a new level of control on the "air lasing" based on nitrogen ions, which can find potential applications in optical remote sensing.
环境空气中由800纳米飞秒激光泵浦的单电离氮分子会产生超辐射发射。在此，我们通过在氮气等离子体内以不同强度比注入一对共振种子脉冲来研究这种超辐射。当精细调整两个种子脉冲之间的延迟时，观察到391.4纳米超辐射发射有1.3飞秒周期的强烈调制。当第二个种子脉冲比第一个更强时，调制对比度随延迟时间先增加后减小，且当第二个种子脉冲更强时，最大调制对比度出现在更长的延迟时间。这揭示了种子脉冲后宏观极化随时间的增加。此外，这些观测结果为基于氮离子的“空气激光”提供了新的控制水平，其在光学遥感中具有潜在应用。
