Light scattering in opal heterojunctions

Light propagation in photonic hetero-crystals, consisting of two opal films with different lattice constants, has been investigated in the realistic regime of weak scattering, when the main light flux is transported by ballistic photons. The light scattering at the photonic bandgap interface is studied in combination with transmission data. The spectra and directionality diagrams of scattered light of single- and hetero-opal films are compared. The rate of decrease of the scattering intensity as a function of the scattering angle has been used to quantify the scattering strength. The anisotropy of the interface scattering is identified by deducing the trajectories of single scattered photons from scattered light spectra. It is found that the weak scattering regime is preserved in the hetero-opal. Moreover, the diffusively scattered light leaving the double-film is mostly generated in the film, which faces the detector.