Observation of the optical <inline-formula><tex-math><?CDATA ${{\rm{X}}}^{2}{\Sigma }_{{\rm{g}}}^{+}$?></tex-math><mml:math><mml:mrow><mml:msup><mml:mi mathvariant="normal">X</mml:mi><mml:mn>2</mml:mn></mml:msup><mml:msubsup><mml:mo>Σ</mml:mo><mml:mi mathvariant="normal">g</mml:mi><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> <inline-graphic xmlns:xlink="https://www.w3.org/1999/xlink" xlink:href="cpb_28_12_123301_ieqn1.gif"/></inline-formula>–A2Πu coupling in <inline-formula><tex-math><?CDATA ${{\rm{N}}}_{2}^{+}$?></tex-math><mml:math><mml:mrow><mml:msubsup><mml:mi mathvariant="normal">N</mml:mi><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> <inline-graphic xmlns:xlink="https://www.w3.org/1999/xlink" xlink:href="cpb_28_12_123301_ieqn2.gif"/></inline-formula> lasing induced by intense laser field<xref rid="cpb_28_12_123301fn1" ref-type="fn">*</xref><fn id="cpb_28_12_123301fn1"><label>*</label>Project supported by the National Natural Science Foundation of China (Grant Nos. 61625501, 11904121, and 61427816), the Open Fund of the State Key Laboratory of High Field Laser Physics (SIOM), China, the Program for JLU Science and Technology Innovative Research Team (JLUSTIRT), China (Grant No. 2017TD-21), and Fundamental Research Funds for the Central Universities of China.</fn>

Observation of the optical

X2Σg+

–A²Π_u coupling in

N2+

lasing induced by intense laser field**

Project supported by the National Natural Science Foundation of China (Grant Nos. 61625501, 11904121, and 61427816), the Open Fund of the State Key Laboratory of High Field Laser Physics (SIOM), China, the Program for JLU Science and Technology Innovative Research Team (JLUSTIRT), China (Grant No. 2017TD-21), and Fundamental Research Funds for the Central Universities of China.

Wang Siqi¹, Fu Yao¹, Yao Danwen¹, Chen Shanming¹, Zhang Wei¹, Li Helong^{1, 2, †}, Xu Huailiang^{1, 3, ‡}

(a) Typical fluorescence spectrum in pure N₂ gas induced by the laser field of the pump and coupling pulses obtained with θ = 90°, (b) the intensity of the 391-nm fluorescence versus the angle θ between the polarization directions of the coupling pulse and the pump pulse.