Tripathy 9619373 The principal objective of this grant is the detailed investigation of a novel phenomenon recently observed under NSF-DMR funding. A number of NLO polymers with tailored molecular architectures including Interpenetrating Polymer Networks were fabricated. A large number of the NLOphores incorporated in these systems were based on azo dyes. In fact azo chromophores have been extensively employed in designing NLO polymers over the past decade. In the course of the study on optical recording under NSF-DMR funding, laser-induced surface relief holographic grating formation on a number of azo-dye containing polymer films was observed. Large amplitude (>1000 A) holographic surface relief gratings on azobenzene containing NLO polymer films were optically produced significantly below the glass transition temperature without any subsequent processing steps. It has been established that the recording is not due to a thermal process. Early research also indicates strong polarization-dependent writing behavior. Such large scale motion of polymer chains significantly below Tg and its relationship to incident light polarization and intensity variation is unusual and begs careful study and interpretation of the phenomenon. The focus of this proposal is 1) to design and synthesize polymers with different chemical structures and 2) to investigate the surface grating formation process under a variety of optical exposure conditions to explore the mechanism of this novel process. The role of each structural element (i.e., the chromophore side groups, the polymer backbone, and the spacers between them) will be systematically investigated in these polymers. The roles of photo-induced processes of the chromophores (such as photoisomerization and photo-induced orientation of the azobenzene groups) in creation of the relief gratings will be examined. Cooperative motions of the polymer backbones along with the chromophores will be investigated. The effect s of changing wavelength, intensity, and polarization of the writing beams will be explored. A comprehensive experimental investigation of the mechanism will help establish a theoretical model for the process. %%% This project will provide fundamental understanding in the area of novel surface-grating techniques for electro-optical applications. ***
