Space-time wave packets propagating a kilometer in air

We report on the diffraction-free propagation of space-time wave packets (STWPs) -a class of propagation-invariant pulsed beams -for ∼ 1 km in an open-air laser range in a low-turbulence scenario. Making use of ≈ 100-fs pulses (bandwidth ∼ 25 nm) at a wavelength of ≈ 1 µm, we construct an STWP with a transverse width of ≈ 2 mm that expands to ≈ 3 mm after ∼ 500 m, and another that expands from ≈ 8 mm to ≈ 10 mm after 1 km. The propagation of the STWPs is compared to Gaussian wave packets of the same transverse spatial width and bandwidth. We establish a theoretical model that accounts for the significant factors limiting the STWP propagation distance and suggests a path to further extending this distance.