Diffraction-based rainbow
The picture shows an example of spectrum-invariant propagation. It was produced in the diffraction of a spatially coherent and collimated white-light beam from an amplitude radial grating. The pattern is shape (and spectrum) invariant under propagation and demonstrates colorful radial Talbot carpet at the transverse plane. [For additional information see S. Rasouli et al., Opt. Express 27, 17435-17448 (2019).]
—Saifollah Rasouli, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran