Excitonic optical nonlinearity of dielectric nanocomposites in weak optical fields

The paper presents a model of optical nonlinearity in a dielectric nanoсomposite for wavelengths ranging from 200 to 800 nm and intensities of up to 1000 W/cm$^2$. Results of the numerical modeling of the optical response in a nanocomposite consisting of dielectric nanoparticles Al$_2$O$_3$ with low volume concentration (of the order of 0.3%) embedded in a transparent dielectric liquid matrix are presented. It is found that with the volume concentration remaining unchanged, the value of nonlinear response in unit volume increases with decreasing nanoparticles size. The spectrum of the nonlinear extra term of the refractive index is shown to be affected by various parameters, such as the size and anisotropy of nanoparticles. It is notable that for 45-nm Al$_2$O$_3$ nanoparticles with 0.3% volume concentration the value of the nonlinear optical response reaches $1.5*10^{–4}$ cm$^2$/W near the resonant absorption band.