Abstract
It is shown that the polycrystalline structure of self-assembled synthetic opals leads to an interplay of properties determined by order and disorder in the vicinity of the optical stop band. We analyze the balance of photon fluxes by studying angle-resolved spectra of diffracted and scattered light for all directions in space. It is shown that the shape of the stop band features in different types of optical spectra ~diffraction, transmission, and scattering! is interlinked and must be studied jointly to understand optical phenomena in these materials. The principal effects are ~i! angular dispersion of the photonic stop bands in diffraction spectra, ~ii! inhomogeneous broadening of the stop band in zero-order transmission, and ~iii! appearance of very strong peaks in the spectra of scattered light, with resonant enhancements observed with intensity up to ;10 times greater than background scattering levels. It is shown that the resonant enhancements arise from multiple incoherent backward/forward reflections between the microcrystallites. It is shown that the spatial pattern and spectral form of the scattering spectra can be deduced from the analysis of angle-resolved zero-order transmission spectra under conditions where the attenuation length of light within the stop band is comparable to the thickness of the sample. The methodology of the studies developed in this paper is applicable to a wide class of disordered photonic crystal structures.
Published Version
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