Li Helong, Hou Mengyao, Zang Hongwei, Fu Yao, Lötstedt Erik, Ando Toshiaki, Iwasaki Atsushi, Yamanouchi Kaoru, Xu Huailiang
State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Phys Rev Lett. 2019 Jan 11;122(1):013202. doi: 10.1103/PhysRevLett.122.013202.
We show that the intensity of self-seeded N_{2}^{+} lasing at 391 nm, assigned to the B^{2}Σ_{u}^{+}(v^{'}=0)→X^{2}Σ_{g}^{+}(v^{''}=0) emission, is enhanced by 2 orders of magnitude by modulating in time the polarization of an intense ultrashort near-IR (40 fs, 800 nm) laser pulse with which N_{2} is irradiated. We find that this dramatic enhancement of the 391 nm lasing is sensitive to the temporal variation of the polarization state within the laser pulse while the intensity of the spontaneous fluorescence emission at 391 nm is kept constant when the polarization state varies. We conclude that a postionization multiple-state coupling, through which the population can be transferred from the X^{2}Σ_{g}^{+} state of N_{2}^{+} to the first electronically excited A^{2}Π_{u} state, leads to the depletion of the population in the X^{2}Σ_{g}^{+} state, and consequently, to the population inversion between the X^{2}Σ_{g}^{+} state and the B^{2}Σ_{u}^{+} state.
我们表明，分配给B²Σᵤ⁺(v' = 0)→X²Σ₉⁺(v'' = 0)发射的391 nm处自种子N₂⁺激光的强度，通过对用于照射N₂的强超短近红外（40 fs，800 nm）激光脉冲的偏振进行时间调制，增强了2个数量级。我们发现，391 nm激光的这种显著增强对激光脉冲内偏振态的时间变化敏感，而当偏振态变化时，391 nm处自发荧光发射的强度保持恒定。我们得出结论，一种后电离多态耦合，通过它可以将N₂⁺的X²Σ₉⁺态的粒子数转移到第一电子激发态A²Πᵤ，导致X²Σ₉⁺态的粒子数耗尽，从而导致X²Σ₉⁺态和B²Σᵤ⁺态之间的粒子数反转。
