The propagation distance of a pulsed beam in free space is ultimately limited by diffraction and space-time coupling. Space-time (ST) wave packets are pulsed beams endowed with tight spatio-temporal spectral correlations that render them propagation-invariant. Here we explore the limits of the propagation distance for ST wave packets. Making use of a specially designed phase plate inscribed by gray-scale lithography, we synthesize an ST light sheet of width $approx700$~$mu$m and bandwidth $sim20$~nm and confirm a propagation distance of $approx70$~m.
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