# Non-diffracting broadband incoherent space-time fields

## TL;DR

This paper demonstrates that structuring the spatio-temporal spectrum of incoherent light creates broadband, diffraction-free fields with controllable spatial features, opening new avenues for optical coherence studies.

## Contribution

It introduces a method to generate broadband incoherent space-time fields that are diffraction-free through spectral engineering, extending coherence control to incoherent light.

## Key findings

- Incoherent space-time fields can be diffraction-free with structured spectra.
- The spatial feature's width and amplitude are tunable via spectral engineering.
- The approach enables new experimental studies of optical coherence in structured fields.

## Abstract

Space-time (ST) wave packets are coherent pulsed beams that propagate diffraction-free and dispersion-free by virtue of tight correlations introduced between their spatial and temporal spectral degrees of freedom. Less is known of the behavior of incoherent ST fields that maintain the spatio-temporal spectral structure of their coherent wave-packet counterparts while losing all purely spatial or temporal coherence. We show here that structuring the spatio-temporal spectrum of an incoherent field produces broadband incoherent ST fields that are diffraction-free. The intensity profile of these fields consists of a narrow spatial feature atop a constant background. Spatio-temporal spectral engineering allows controlling the width of this spatial feature, tuning it from a bright to a dark diffraction-free feature, and varying its amplitude relative to the background. These results pave the way to new opportunities in the experimental investigation of optical coherence of fields jointly structured in space and time by exploiting the techniques usually associated with ultrafast optics.