Air lasing with structured light fields*

Air lasing is a cavity-free lasing process generated from the laser filamentation, offering a simple and efficient way for remotely generating coherent light with substantial potential for optical remote sensing. Air lasing arises from a variety of complex physical processes with nitrogen ion lasing being of particular interest. Yet, many of its observed phenomena have not been well understood. Traditionally, researchers have driven air lasing with fundamental Gaussian beams, focusing studies primarily on time-domain aspects, whereas the spatial coherence is ignored. . Here, we introduced structured light fields, vector and vortex beams, into air lasing research, aiming to explore its underlying physical mechanisms from both temporal and spatial perspectives. In the scheme employing only a single driving beam, we successfully generated the ultraviolet vector and vortex air lasing of N₂⁺, ruling out the hypothesis of the second harmonic acting as the self seed. In the pump-seed scheme, we demonstrated that the spatial helical phase was transferred from the pump to the seed beam, and as a result, the topological charge of the observed air lasing is the sum of the pump and the seed, which suggests a new underlying mechanism that has yet to be uncovered. Our research not only provides a time-space coupling perspective for understanding air lasing but also pioneers a novel technology for generating ultraviolet structured light fields.