Photoinduced anisotropies in the absorption and the refractive index of aromatic azo compound doped polymer films

Aromatic azo molecules (AAMs) undergo a reversible process known as {dollar}transrightarrow cis{dollar} isomerization, due to interaction with highly absorbed optical fields. The terms trans and cis describe two minima in the ground state energy of an AAM, each minimum exhibiting a characteristic absorption spectra and molecular structure. {dollar}Transrightarrow cis{dollar} isomerization, therefore, involves a change in energy as well as a physical alteration of the structure of the molecule. When placed in a polymer matrix, illumination with an optical field of the proper wavelength, induces anisotropic changes in the absorption and refractive index of the bulk material. Information can be written, erased, and rewritten to these materials multiple times via this process. Although the chemistry of the individual components of this system is fairly well understood, the process of optically inducing linear diattenuation and linear retardance in these materials has not yet been the subject of careful examination.; The aim of this research was to investigate the interaction of AAM doped polymer films and optical fields. Methyl orange doped polymer films, fabricated by spin coating, were examined. The spectral absorption of the films was measured in a CARY spectrophotometer and a pumped rotating sample polarimeter was constructed to measure the linear diattenuation and linear retardance induced in the films during illumination. The information gained from these experiments was used to construct a model of the interaction of AAMs and optical fields. This model was then applied to the formation of holographic gratings in these films.; AAM doped polymer films were found to be sensitive to both the intensity and the state of polarization of an optical field. Linear diattenuation and linear retardance were induced in the films by a linearly polarized optical field, whereas a circularly polarized optical field erased anisotropies in the films. These effects are attributed to the alignment of the aromatic azo molecules due to repeated {dollar}transrightarrow cis{dollar} isomerization and relaxation of the dopant molecules within the film. Holographic recording with both parallel and orthogonally polarized optical fields was demonstrated and is attributed to the polarization sensitivity of the AAM doped films.