Studies of coherent backscattering from opal photonic crystals

We studied the coherent backscattering (CBS) of light from synthetic opal photonic crystals with incomplete photonic gap. For incident angles far from the Bragg angle, we found that the CBS cones are similar to those observed in previous measurements of various random media and in excellent agreement with theory. However, for incident angles close to the Bragg angle, we observed a substantial broadening of the CBS cone. This broadening is due to the light intensity decay in course of propagation along the Bragg direction. We also measured the wavelength dependence of the CBS cone from opals and compare it to that of TiO2 particle suspensions.