Fig. 1: Chiral Bragg diffraction from flat and spherical cholesterics.

a Schematic drawing of the helically modulated structure (rods represent n, color-coded blue→red for n parallel→perpendicular to the image plane) of a cholesteric liquid crystal and the resulting wavelength- and polarization-selective reflection due to Bragg diffraction. Grey arrows represent unpolarized white incident light at different incidence angles θ with respect to m, each corresponding reflection colored to the wavelength that is Bragg-diffracted at that θ. Since the helix is drawn right-handed, the reflected light would have right-handed circular polarization. b Schematic cross section of CSR beads (or droplets) with radial helix orientation, a point defect (black) at the core, and arbitrarily oriented Frank-Pryce defect lines (semi-transparent grey). If the retroreflection wavelength is red (central spot in top view), the cross communication is green. Since the latter happens throughout the bead at different depths, radial lines result³³. c Schematic cross section of polymerized and punctured CSR shells, defect-free since shells have no point defect and the Frank-Pryce defect line is removed upon puncturing. Shells illuminated from the thin side primarily produce internal selective reflection rings³⁹, but some cross communication (spots rather than lines, due to the isotropic core³⁵) may also be seen, as in the top view example (unpunctured shell). Color coding of director orientation in (b-c) is as in (a)