| Summary: | The distant projection of high-peak and average-power laser beams in the atmosphere is a long-standing goal with a wide range of applications. Our early proof-of-principle experiments [Phys. Rev. X 4, 011027 (2014)PRXHAE2160-330810.1103/PhysRevX.4.011027] presented one solution to this problem, employing the energy deposition of femtosecond filaments in air to sculpt millisecond-lifetime sub-meter-length air waveguides. Here, we demonstrate air waveguiding at the 50-m scale, 60×longer, making many practical applications now possible. We employ a new method for filament energy deposition: multifilamentation of Laguerre-Gaussian LG_{01} “donut” modes. We first investigate the detailed physics of this scheme over a shorter 8-m in-lab propagation range corresponding to 13 Rayleigh lengths of the guided pulse. We then use these results to demonstrate optical guiding over 45 m in the hallway adjacent to the lab, corresponding to 70 Rayleigh lengths. Injection of a continuous-wave probe beam into these waveguides demonstrates very long lifetimes of tens of milliseconds.
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