Uklein A. Optical and nonlinear optical properties of composite media with incorporated organic and inorganic nanoobjects

In this work the analysis was performed of optical properties and nonlinear optical (NLO) response mechanisms in composite media based on soft matrices due to the self-action of CW and pulsed laser radiation. The nanoscale objects such as amorphous TiO2 nanoparticles (NPs) and polymer-azo-dye complex (PADC) incorporated to polymer polyhydroxyethyl-methacrylate (pHEMA) and nematic liquid crystal (LC) 5CB matrices correspondingly were studied. For the first time the quantum yield of photoinduced charge separation tetta ~ 50% at TiO2/polymer interface was observed in the hybrid system pHEMA:TiO2 with NPs with less size and dispersion 2±0.5 nm under the excitation of nanosecond laser pulses at 355 nm. It was shown that the generation of Ti3+ centers within the UV irradiation effects in the negative photoinduced refractive index variation delta n <0 with high delta n contrast in the IR (1310 nm) spectral range versus the visible and UV one due to the weak absorption. The analysis of Ti3+ center polarizability, cubic hyperpolarizability and specific elastic scattering losses reveals the NPs concentration 4.4*1017 cm-3 in pHEMA:TiO2 hybrids to be optimal for applications in fields of photonics and nonlinear optics. The analysis of the LC:PADC nanocomposite NLO response was shown that its magnitude and sign strongly depend on the laser radiation intensity and the PADC concentration. Its efficiency is higher versus the components NLO responses in isotropic solution and LC matrix: up to 3-6 times in CW and up to 5-10 times in pulsed excitation regimes. The following photoinduced mechanism with the PADC concentration rise were revealed: (i) photoorientation of the PADC; (ii) trans-cis-trans isomerization; (iii) the complex aggregation effect.