Interference suppression of light backscattering through oblique deposition of a layered reflecting coating: bi-layer on a substrate

We theoretically demonstrate the possibility of entirely suppressing light backscattering towards the incident beam from a rough bilayer fabricated by deposition at an oblique angle, such that the substrate relief is replicated at a certain angle to the substrate surface. The necessary conditions of the scattering suppression were formulated. Interference suppression was observed experimentally (633 nm wavelength, 45° incidence angle, −35° scattering angle) with a set of SiO2-on-Ta2O5 bi-layers fabricated at different deposition angles. We detected a suppression of the scattering from the bi-layer fabricated at the deposition angle of 7.7° by a factor of about 30 compared with that from the sample deposited at normal incidence. The observed value of the scattering suppression was limited by the background noise of the measurements.