2025/02/03 by Gao, Jingsong, Wang, Yang, Dong, Jiahao +5
#Atomic Physics (physics.atom-ph) #FOS: Physical sciences #Optics (physics.optics)
paper · doi:10.48550/arxiv.2502.01414
A single intense near-infrared femtosecond laser beam can remotely generate ultraviolet N2+ lasing in the air, offering a promising light source in the atmosphere. One of the key debates regarding its mechanism is whether it is seeded by a self-generated spectral component, such as the second harmonic, which is inevitably produced by the charge gradient in the laser plasma filament. In this study, we generated both radially and azimuthally polarized N2+ lasing at 391 nm driven by a single 800-nm cylindrical vector beam. Subsequently, the same vector beam was employed to drive argon for the second harmonic generation. The radially polarized pump beam can produce radially polarized second harmonics with higher radial order, while the azimuthally polarized pump beam yields no second harmonic generation, owing to the special mechanism of the ponderomotive effect. The absence of azimuthally polarized second harmonic strongly ruled out the hypothesis of self-seeding by the second harmonic because radially and azimuthally polarized N2+ lasing signals show comparable intensities. By characterizing the spatial phase distribution of the vector 391-nm lasing, we concluded that the phase of the 391-nm lasing is synchronized with the driving field. The experimental results suggest that amplified spontaneous emissions are the origin of N2+ air lasing, which was effectively demonstrated by theoretical simulations. Our work also provides a promising method for remotely generating vectorially structured ultraviolet light fields.