Chen Yewei, Lei Hongbin, Wang Quanjun, Xie Hongqiang, Zhang He, Lu Xu, Zhang Ning, Huang Shunlin, Wu Yuzhu, Liu Jianpeng, Zhang Qian, Liu Yi, Zhao Zengxiu, Zhao Jing, Yao Jinping
State Key Laboratory of High Field Laser Physics, <a href="https://ror.org/03g897070">Shanghai Institute of Optics and Fine Mechanics</a>, <a href="https://ror.org/034t30j35">Chinese Academy of Sciences</a>, Shanghai 201800, China.
School of Optical-Electrical and Computer Engineering, <a href="https://ror.org/00ay9v204">University of Shanghai for Science and Technology</a>, Shanghai 200093, China.
Phys Rev Lett. 2024 Sep 13;133(11):113201. doi: 10.1103/PhysRevLett.133.113201.
Tunneling ionization, a fascinating quantum phenomenon, has played the key role in the development of attosecond physics. Upon absorption of a few tens of photons, tunneling ionization creates ions in different excited states and even enables the formation of population inversion between ionic states. However, the underlying physics is still being debated. Here, we demonstrate a significant enhancement in the efficiency of multiphoton excitation when ionization of neutral molecules and resonant excitation of ions coexist in strong laser fields. It facilitates the dramatic increase in population inversion and lasing radiation in N_{2}^{+} around 1000 nm pump wavelength. Utilizing the ionization-coupling theory, we discover that the synergistic interplay between tunneling ionization and multiphoton excitation enables the ionic coherence to be maximized by phase locking of the periodically created ionic dipoles and consistently maintain an optimal phase for the follow-up photoexcitation. This Letter provides new insights into the photoexcitation mechanism of ions in strong laser fields and opens up a route for optimizing ionic lasing radiations.
隧穿电离是一种引人入胜的量子现象，在阿秒物理学的发展中发挥了关键作用。在吸收几十光子后，隧穿电离会产生处于不同激发态的离子，甚至能够在离子态之间形成粒子数反转。然而，其背后的物理机制仍在争论之中。在此，我们证明，当中性分子的电离与离子的共振激发在强激光场中共存时，多光子激发的效率会显著提高。这促进了在1000纳米泵浦波长附近N₂⁺中粒子数反转和激光辐射的急剧增加。利用电离耦合理论，我们发现隧穿电离与多光子激发之间的协同相互作用能够通过对周期性产生的离子偶极子进行锁相使离子相干性最大化，并始终为后续的光激发保持最佳相位。本信函为强激光场中离子的光激发机制提供了新见解，并开辟了一条优化离子激光辐射的途径。
