AUTHOR=Chen You , Man Xiaoman , Liu Binxian , Lin Zhiyang 

TITLE=Nitrogen fluorescence emission pumped by femtosecond optical vortex beams

JOURNAL=Frontiers in Physics

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1124026

DOI=10.3389/fphy.2023.1124026

ISSN=2296-424X

ABSTRACT=An experimental investigation on nitrogen fluorescence emissions pumped by a single 800 nm femtosecond optical vortex (OV) beam with different topological charges (TC) is reported. It is found that the intensity of the two prototype emission lines from neutral nitrogen molecules (N2) and molecular nitrogen ions (N2+), i.e., 337 nm and 391 nm, respectively, shows different TC dependences: the former slightly decreases as the TC increases, while the latter sharply decreases as the TC changes from zero to no-zero, suggesting that the role of the collision-induced process in the formation of the N_2 (C^3 Π_u) and N_2^+ (B^2 Σ_u^+)  states can be dismissed and the self-seeded effect is suppressed when using OV beam. This is confirmed by examining the dependences of the 337-nm and 391-nm emission intensity on pulse energy and gas pressure, and the formation of the N_2 (C^3 Π_u) and N_2^+ (B^2 Σ_u^+) are attributed to dissociative recombination and multi-photon ionization, respectively. Our study highlights that the OV beam can be used as a unique tool to inspect and manipulate the formation dynamics of nitrogen fluorescence emissions and thus the lasing action.