# Broadband space-time wave packets propagating 70 m

## TL;DR

This paper demonstrates the creation of space-time wave packets that can propagate in free space for approximately 70 meters, significantly extending previous limits by using a specially designed phase plate.

## Contribution

The study introduces a novel method to synthesize space-time wave packets with extended propagation distances using gray-scale lithography.

## Key findings

- Propagation distance of ~70 meters achieved
- Synthesized ST wave packet with ~700 μm width and 20 nm bandwidth
- Propagation-invariant behavior confirmed over extended distance

## Abstract

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.