Volume holography in optically isomerized polymer media

Thesis (Ph. D.)--University of Rochester. Institute of Optics, 2004.In optically isomerized polymer media, holograms are recorded through the Quantum Amplified Isomerization (QAI) of a molecule attached to a fully polymerized host matrix. This class of materials has two theoretical advantages over conventional photopolymers: dimensional stability and unlimited thickness. After an introduction to the QAI reaction mechanism, a theoretical model of holographic exposure dynamics in the QAI material is developed. This model is based on measurements of the refractive index of bulk samples as a function of flood exposure energy. It is shown that the refractive index of the QAI material is linearly proportional to chemical conversion. Rigorous coupled wave analysis is then employed to accurately predict the diffraction efficiency of holographic gratings as the index profile saturates and becomes non-sinusoidal. Samples of the QAI material were made from 10 to 20 microns thick by solvent evaporation and from 0.5 to 10 millimeters thick by vinyl polymerization. These samples were used to test the validity of the exposure model; measure material properties such as sensitivity, dimensional stability and optically induced index change; explore the angular resolution limits of volume gratings; and demonstrate resolution-limited angular multiplexing. The exposure model was able to predict the refractive index of the material as a function of optical exposure energy. The highest observed sensitivity, fractional dimensional stability, and optically induced index change were 7500 centimeters per Joule, -0.008, and 0.0053 respectively. Angular spectra measured in 0.80 and 1.40 millimeter thick QAI samples were found to agree with the theoretical resolution limit of a sinusoidal grating with an average absorption coefficient of 5 per centimeter at a write wavelength of 458 nanometers. Gratings were multiplexed at the angular resolution limit of one resolvable hologram every 0.075 degrees read at 633 nanometers in a 1.40 millimeter thick sample. Future chemistry research should focus on more dimensionally stable formulations and a fixing mechanism for the material, while optics research should exp]ore applications such as waveguide structures and gradient index lenses