Large depth-of-focus via programmable space-time light sheets

The diffraction-free property of space-time wave packets has led to an abundance of interest in the field of optical physics. This feature may also find utility in applications for biomedical optics. Specifically, the programmability of the space-time light sheet can yield µm-thick light sheets with widths that resist diffraction in free space over several millimeters, whereas similarly sized Airy, Bessel, or Gaussian light sheets diverge significantly when focused to reach comparable widths. Here, we experimentally and numerically demonstrate this, and confirm that a 10-µm-thick space-time light sheet, achieved without a focusing lens and synthesized by tuning the spectral tilt angle of the light cone, maintains its width over a free-space propagation distance of 2 mm. In comparison, we find that over the same propagation distance, the Airy, Bessel, and Gaussian light sheets, all with starting thicknesses of ∼10 µm, become ∼4.5× to ∼10× wider, respectively. Space-time light sheets thus offer an opportunity for significantly extended depth-of-focus for light sheet microscopy.