Broadband space-time wave packets propagating 70  m

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 and having a laser-damage threshold of ∼0.5  J/cm², we synthesize a ST light sheet of width ≈700  μm and bandwidth ∼20  nm, and confirm a propagation distance of ≈70  m.