Angle-resolved reflectivity of single-domain photonic crystals: effects of disorder.
Angle-resolved reflectivity has been measured from single-domain photonic crystals consisting of air spheres in a TiO2 backbone. Monochromatic beams are focused to a 10 microm spot, and kept on the rotation axis with a precision better than 10 microm. We report high reflectivity up to 94% and surface domains as large as 200 microm, with a mosaic spread of +/-3 degrees. The maximum reflectivity at normal incidence agrees well with theoretical calculations in the scalar-wave approximation, extended to include an extinction length due to diffuse scattering, that is obtained from independent experiments. The angle-resolved stop bands compare favorably with previous measurements using coarse beams as well as with prior theoretical calculations. Inhomogeneous broadening introduced by coarse beams in previous measurements is found to be small. Our results can only be understood if we assume multiple Bragg diffraction from more than one family of planes simultaneously to take place.