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Angle-resolved retroreflection: what can it tell us about optical properties of three-dimensional photonic crystals?

The retroreflection spectroscopy have been developed with the aim to investigate the spectra of light scattered at intrinsic defects of photonic crystals. Self-assembled 3-dimensional colloidal crystals, opals, have been investigated. Compared to conventional spectroscopies of reflected and transmitted light, which evaluate the rejected by photonic crystal light, the retroreflectance is designed to visualize the propagating eigenmodes of photonic crystals. The principal advantages of this method are the direct experimental evaluation of the stop-bandwidth and the quantitative estimate of defect concentration by the slope of the angle diagram of the scattered light intensity. The added value of this method is the independent evaluation of the periodicity and the effective refractive index of photonic crystals under interrogation by simultaneous observation of the angle dispersions of volume and surface resonances of the photonic crystal lattice.