A gem-quality opal

PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Condensed Matter, Materials & Soft Matter · Interference and diffraction

Condensed Matter Physics, Ch Soft matter: when entropy, not bonding, sets the structure

Problem

A gem-quality opal, illuminated straight on, reflects most strongly at

610\,\mathrm{nm}

(orange). Modelling it, like the chapter's own opal, as a face-centred cubic packing of touching silica spheres with an effective refractive index of

1.35

, estimate the diameter of the spheres that make it up.