Prokopets V. Linear and nonlinear optical properties of composite ceramic materials based on SiC, AlN and Si3N4.

Thesis contains results of comprehensive investigations of crystalline and phase structure, linear and nonlinear optical properties of composite ceramic materials based on SiC, AlN, and Si3N4. The linear optical properties (refractive and extinction index, optical conductivity) were determined in wide spectral range (0,230 - 25 ). The values of the energy gap for SiC, AlN, and Si3N4 ceramics were calculated using optical conductivity data. The effective values of the energy gap for composite SiC+AlN ceramics were estimated, the dependence on AlN concentration were determined. The analysis of linear optical properties by Bruggman effective-medium approximation allows estimating an influence of admixtures on the phase composition and optical properties of the composite ceramics. It has been shown that, by analyzing the dispersion of the refractive index in the effective medium approximation, it is possible to estimate the amount of oxygen in the Si3N4-based ceramics. The experimental and theoretical investigation of surface second harmonic generation in reflection from SiC, AlN SiC+20%AlN, SiC+50%AlN and Si3N4 are presented. The angular dependences of second harmonic generation are in good quality agreement with observations on SiC, AlN. The comparisons of experimental and theoretical second harmonic generation data for composite ceramics SiC+20%AlN, SiC+50%AlN show as quantitative as well as qualitative disagreement. The disagreement points at the necessity of improving the theoretical model of the composite ceramic nonlinear polarization. The good quality agreement between experimental and theoretically calculated data of surface second harmonic generation in reflection from silicone nitride shows that second harmonic generation was caused by electric-quadrupole nonlinear polarization.