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Optical properties of transparent matrix composites containing metal nanoparticles coated with an oxide shell were numerically simulated based on the Aden-Kerker theory applicable for concentric spheres. Using pentaerythritol tetranitrate composites (containing Al/Al2O3 nanoparticles) as an example, the linear scattering and absorption coefficients as well as the total reflectance and transmittance and collimated beam transmittance were shown to be determined by the sample thickness, the nanoparticle radius, the mass fraction of nanoparticles, and mass fraction of the oxide in the nanoparticles. An approach to determining the said parameters based on the comparison of the calculated spectral dependencies of the reflectance and transmittance with the experimental ones was suggested. The nanoparticle radius was determined with the minimum error (of about 2 – 3 %), while the nanoparticle mass fraction and oxide mass fraction were weak parameters determined with a 25 % error.

Optical properties of a model pressed composite (potassium bromide matrix with incorporated ALEX aluminium powder) are experimentally investigated. It is shown that the spectral dependences of total transmittance and diffuse reflectance can be described with allowance for the presence of both individual aluminium nanoparticles and their aggregates with a characteristic radius of 133 nm in a sample. It is found that irradiation of a composite sample by a 1070-nm cw laser initiates nonlinear absorption of radiation by aluminium particles, which is detected by a change in the sample optical density. A model is proposed to describe the effect, which is based on the sample heating and temperature dependence of the optical characteristics of aluminium particles. The calculation results are in qualitative agreement with the observed changes in optical density; hence, the thermal mechanism of nonlinear absorption of electromagnetic radiation by metal particles is applicable to this model system.