Photonic crystals: Growth, characterization and non-linear optical effects.

摘要

Photonic band gap materials (or photonic crystals) are periodic dielectric structures with periodicities comparable to the wavelength of light. They offer promising solutions to various scientific and technological challenges. The work in this thesis is focused on fabrication and characterization techniques for photonic crystals and the study of linear and nonlinear optical phenomena in these periodic structures.; A brief theoretical background of photonic band gap materials is provided in chapter 1. Chapter 2 describes a method for the fabrication of highly ordered photonic crystals by using self-assembly of colloids of dielectric spheres. In this chapter, the conditions that increase the level of perfection and the factors that give better control over the crystallization process are investigated and their theoretical interpretations are discussed. Also infiltration of a high refractive index material (GaP) into the crystals is investigated.; Methods for generation of third harmonics in two different photonic crystal media are presented in chapter 3. In the first case, observation of a highly enhanced one-step, third-harmonic generation in three dimensional photonic crystals formed by close-packed polystyrene spheres in a face centered cubic arrangement, is presented. A near infrared laser beam, with a wavelength range of 1300nm-1900nm, is used as the pump source. In the second case, a strong enhancement of one-step third-harmonic generation in a one dimensional photonic crystal is presented. In this case, a near infrared laser beam is tuned to the low frequency edge of the band gap of a photonic crystal prepared from polymer dispersed liquid crystals by holographic lithography.; Chapter 4 presents the results of linear and nonlinear optical studies in photonic crystal alloys which are formed by various compositions of polystyrene and polymethlymethacrylate colloidal spheres of the same size. Linear transmittance and reflectance measurements as well as third-harmonic generation experiments were conducted in these photonic crystal alloys. The observed experimental result is fitted to a calculated plot by assuming an effective dielectric constant for the colloidal spheres.; In chapter 5, another promising method of fabrication of photonic crystals, holographic lithography, is described. A procedure and optimum growth parameters for the fabrication of fcc-like photonic crystals are presented.; Summary and future plans related to the work in this thesis are given in the conclusions and future work section.