Figure 5
From: A special three-layer step-index fiber for building compact STED systems
Optical power distribution on a cross-section (not focal plane) of the focused beam. (a) Shows a schematic diagram of the setup: the output light beam of special fiber was focused by a lens and then captured by a CCD camera. (b) Is a photo taken by CCD camera. It indicated the output light beam can maintain a decent doughnut-shaped cross-section when focused by lens.
