Disorder behavior in nano- and submicron-structured polymeric composite systems with passive and active dielectric media.

摘要

This project aims to investigate the influence of disorder on the optical properties of passive and active disordered dielectric media. The theoretical investigation has been carried on the effect of position and size disorders on two-dimensional passive and active disordered dielectric systems with circular inclusions based on the time-dependent theory, which combines the time-dependent Maxwell's equations with the semi-classical laser theory.; Numerically, the influence of the density of scattering particles on the mode distribution of passive ordered and disordered systems is examined. Photonic band gaps formed in the most densely packed ordered systems (particle density = 2x1013m-2) are destroyed when a moderate degree of disorder is introduced into the medium. It shows that a size disorder breaks down a gap more rapidly than position disorder does, which is consistent with previous published results by others. The amplification process of active disordered systems is also investigated. It is found that the laser emissions are suppressed by the photonic band gap. The strength of amplification of electromagnetic wave can be enhanced by increasing the amounts of disorder. The laser emission can also be modified by alternating the relative spectral position of the band gap and the gain profile. The results implicate that the laser emission can be actively controlled by varying the amount of the disorder and the central wavelength of gain profile.; In the photoluminescence experiments, it was found that the slope of the peak emission intensity curve of the colloid solution and PMMA films which consists of laser dye and TiO2 submicron particles changed as the pump energy increased. These results indicate the lasing threshold and saturation behavior of the random laser system. The emission peaks of the colloid solution and PMMA films become narrower when pumping energy is above certain value. Several discrete peaks occurred in the emission spectra when the pump energy was further increased. This significant reduction of line-width and increase of the intensity of the emission peak confirm the existent of lasing threshold.