Rotational, Vibrational, and Electronic Modulations in N_{2}^{+} Lasing at 391 nm: Evidence of Coherent B^{2}Σ_{u}^{+}-X^{2}Σ_{g}^{+}-A^{2}Π_{u} Coupling

Toshiaki Ando; Erik Lötstedt; Atsushi Iwasaki; Helong Li; Yao Fu; Siqi Wang; Huailiang Xu; Kaoru Yamanouchi

doi:10.1103/PhysRevLett.123.203201

Rotational, Vibrational, and Electronic Modulations in N_{2}^{+} Lasing at 391 nm: Evidence of Coherent B^{2}Σ_{u}^{+}-X^{2}Σ_{g}^{+}-A^{2}Π_{u} Coupling

Phys Rev Lett. 2019 Nov 15;123(20):203201. doi: 10.1103/PhysRevLett.123.203201.

Authors

Toshiaki Ando¹, Erik Lötstedt¹, Atsushi Iwasaki¹, Helong Li², Yao Fu², Siqi Wang², Huailiang Xu^{2

3}, Kaoru Yamanouchi¹

Affiliations

¹ Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
² State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China.
³ State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.

PMID: 31809116
DOI: 10.1103/PhysRevLett.123.203201

Abstract

We investigate lasing of a N_{2} gas induced by intense few-cycle near-IR laser pulses. By the pump-probe measurements, we reveal that the intensity of the B^{2}Σ_{u}^{+}-X^{2}Σ_{g}^{+} lasing emission of N_{2}^{+} oscillates at high (0.3-0.5 PHz), medium (50-75 THz), and low (∼3 THz) frequencies, corresponding to the energy separations between the rovibrational levels of the A^{2}Π_{u} and X^{2}Σ_{g}^{+} states. By solving the time-dependent Schrödinger equation, we reproduce the oscillations in the three different frequency ranges and show that the coherent population transfer among the three electronic states of N_{2}^{+} creates the population inversion between the B^{2}Σ_{u}^{+} and X^{2}Σ_{g}^{+} states, resulting in the lasing at 391 nm.