Integrated optics spectroscopy of polymer thin films

This thesis describes the design and construction of an integrated optics (IO) spectrometer for the purpose of characterizing optically transparent polymer thin films (1-10 $ mu$m). IO spectroscopy exploits the properties of electromagnetic fields that exist in a polymer film when it is used as a planar dielectric waveguide. The spectrometer measures waveguide propagation constants and Raman spectra excited by guided modes. These data are used to characterize the structures of solution cast cellulose acetate (CA) films and glassy cellulose films regenerated from them, and laser induced anisotropy in organically modified silicate (ORMOSIL) sol-gel films.Waveguide Raman spectra indicate partial alignment of CA chains within the plane of the film. Deacetylation of CA films in aqueous ammonia to form glassy regenerated cellulose (RC) waveguides preserves orientational anisotropy of the parent CA film. Refractive index profiles are reconstructed from measured optical propagation constants of CA, RC and partially regenerated CA waveguides using inverse Wentzel-Kramers-Brillouin approximation methods. Partially regenerated CA films possess an asymmetric reflective index gradient attributed to depth inhomogeneity present in CA films prior to regeneration.The effects of deviations from right angle scattering geometry on polarized waveguide Raman spectra are discussed. Polarization mode conversion is attributed to the presence of off-diagonal elements in the film dielectric tensor. In CA films, these off-diagonal elements result from excessive pressure on the coupling prism and partial orientation of polymer chains. Coupled mode theory is used to predict the effects of polarization mode conversion on the polarized Raman spectra as a function of film parameters and coupling angle.Photoinduced birefringence and photoalignment are observed in ORMOSIL sol-gel films after exposure to guided light from an argon ion laser (514.5 nm and 488.0 nm lines). By simultaneously exciting TE and TM modes, non-transient, reversible off-diagonal dielectric tensor elements are introduced in the film. These off-diagonal elements cause coupling between the orthogonal TE and TM modes, which is, in turn, observed in polarized waveguide Raman spectra collected from the film. Photorefractive effects are attributed to photoinduced anisotropy (PIA) and glass photosensitivity phenomenon previously observed (by others) in doped silicate glasses