Forward scattering of light in thin opal films

Angle-resolved spectra of the light scattered in a thin opal film have been measured behind the sample in three configurations, which differ by directions of the light incidence and detection. Two minima have been observed in scattering spectra and assigned to the attenuation by the (111) Bragg photonic bandgap along directions of the incident and detected photon flux. The irrelevance of the photonic bandgap minima to the actual path of scattered photon has been demonstrated. The projection of the directional (111) photonic band gap has been allotted to the plateau observed in the angle diagrams of the scattered light intensity. The spectra and the angle diagrams of the scattered light have been interpreted in terms of the weak scattering regime, when scattering serves for coupling a photon from one eigenmode of opal to another.