Outdoor 100-m-scale air waveguides

Abstract

Optical power densities for standoff spectroscopy, remote sensing, directed energy, and free-space optical communications are limited by diffraction and adverse atmospheric conditions such as turbulence, fog, and wind. Air waveguides, generated by ultrashort-pulsed laser filamentation, are a promising approach for transmission and collection of optical signals over long distances, overcoming beam diffraction and, for point-like sources, inverse square signal falloff with distance. In this work, we demonstrate outdoor guiding for the first time over a record length of ~100 m, exceeding the prior (indoor) record of 42 m. We correlate air waveguide performance to a range of real atmospheric conditions including turbulent refractive index structure parameter ($C_n^2$) values up to ~$2.5\times10^{-14} m^{-2/3}$, crosswind speeds up to ~2 m/s, as well as temperature, pressure, and humidity variations. Accompanying propagation simulations provide insight into the real effects of these environmental perturbations, particularly crosswind, on waveguide performance and lifetime. Our results pave the way for quasi-continuous air waveguiding with kHz-scale repetition rate filaments in challenging outdoor environments.