Experimental probe of gaps in photonic crystals

The optical reflectivity and transmission of a large number of photonic crystals made of colloids are measured. A wide range of densities and refractive index ratios of the constituent materials are studied. Detailed information on the crystal quality is obtained by small angle X-ray scattering experiments. Stop gap widths are determined. The widths of the gaps can be described as a measure for the interaction of strength between light and photonic crystals. Full widths at half maximum of Bragg peaks in reflection are shown, and compared to dynamical diffraction theory and photonic band structures. The reflectivity data are in excellent agreement with the theory, and thus a good measure of the stop gap widths.