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The scattering by slightly inhomogeneous objects has been studied by a first-order method and reciprocity theorem. The scattering calculation reported in this manuscript is based on a simple computation of the field in a defectless structure at different incidence angles. The numerical results have been compared to those given by an exact calculation. It is shown that the method enables to handle complex structures with an affordable computational burden. A major advantage of the method is its ability to treat different defects without recomputing the field, i.e, the main part of the computation time. In addition, for defects in periodic structures, the field computation can be limited to a single period thus leading to an important decrease of the computational time and required memory. This method is believed to provide significant advantages for the engineering of optical devices.

International audienceThree-dimensional photonic crystals (PCs) are periodic materials with a modulated refractive index on a length scale close to the light wavelength. This optical property allows the preparation of specific optical components like highly reflective mirrors. Moreover, these structured materials are known to have a high laser-induced damage threshold (LIDT) in the sub-nanosecond range compared to multi-layered dielectric mirrors. This property is obtained because only one high LIDT material (silica) is used. The second material used in the layer stack is replaced by air. In this work, we present the development of 3D PCs with narrow-sized colloidal silica particles, prepared by sol-gel process and deposited with Langmuir-Blodgett technique. Different syntheses routes have been investigated and compared regarding the optical properties of the PCs. Finally a numerical model based on an ideal opal network including defect influence is used to explain these experimental results