Novel photodynamic azo polymers: Optically induced holographic surface-relief-grating formation

This thesis research presents a new photodynamic polymer transport process. In the course of holographic grating recording on azo polymers, it was found that surface relief gratings with large amplitude could be directly produced on the polymer films. The gratings produced on the polymer films showed very regularly spaced sinusoidal surface relief structures. Different amplitude of the surface relief patterns could be obtained by changing the exposure dose. The grating spacing could be controlled by changing the angle between the two writing beams. The gratings were stable below T{dollar}rmsb{lcub}g{rcub}{dollar} of the polymer lasting for several years without decay and could be erased.; While irradiation of linearly polarized visible laser beam results in reorientation of the azo groups leading to birefringence in the polymer film, such a large surface change was not expected due to the alignment of the chromophores alone. Large-scale molecular motion and volume change occurred well below T{dollar}rmsb{lcub}g{rcub}{dollar} of the polymer.; The presence of azobenzene side groups in the polymer structure is a critical structural requirement. Polymers containing chromophores which are not able to undergo photoisomerization or reorientation process showed no large surface change. Therefore, trans-cis photoisomerization and reorientation process is important. Strong electron donor-acceptor structure of the azo chromophore is helpful but not critical. A low Tg azo polymer showed very slow formation of the surface grating.; The photoinduced orientation effects leading to birefringence gratings contributed to the initial rapid increase of the diffraction efficiency. The following stage involves the saturation of orientation grating and partial cancellation of the refractive index grating by the surface modulation. It implies that there is a phase shift between the first birefringence grating and the next surface grating formation process.; The amplitude of the surface relief grating is very strongly dependent on the polarization of the recording beams. The gratings written with p-polarized beams showed significantly larger surface modulation than with s-polarized beams. Gratings recorded with circularly polarized and unpolarized laser beams also resulted in large surface modulations with high diffraction efficiencies. The existence of both light intensity and resultant electric field polarization variation of writing beams is essential. Thermal effects due to light absorption do not play an appreciable role at the intensities used.; The surface pattern from exposure to a straight edge diffraction pattern mapped the negative first derivative of the expected intensity distribution. Surface modulation is due to the lateral molecular migration, not expansion/contraction.; Possible mechanisms are proposed. For net migration of material, spatially-varying forces acting on the polymer chains are expected. The spatially-varying field can be d.c. space charge field generated in the polymer due to charge carrier generation. Space charge fields of the order of a few hundred volts/cm would result in very large forces on the oriented chromophores and hence the polymer chains. (Abstract shortened by UMI.)...