Air Waveguiding of Lasing Induced by Long‐Distance Filament

ABSTRACT The imperative to improve the remote detection efficiency of Lidar technology has motivated research on the directivity of backscattered signals. The nondirectional nature of typical fluorescence poses a significant challenge to remote single‐sided detection based on fluorescence. Here, we demonstrate a highly directional amplified fluorescence confined by a self‐waveguide induced by an air filament at a remote distance. The structure of the waveguide is similar to conventional optical waveguides and is proven to arise from the amplification of fluorescence inside the filament. New phenomena in this work indicate that the directivity could be further optimized to less than 7° by simply extending the propagation distance of the filament. The backward detection efficiency could be improved by two orders of magnitude, compared to conventional isotropic fluorescence. This considerable advantage significantly boosts the detection sensitivity and extends the detection ranges in remote sensing applications.