Search

A new asymmetric polarization holography was conducted to form a blazed surface relief (SR) structure in a polymethacrylate film comprised of 4-methoxyazobenzene side groups using asymmetrically controlled polarized 325 nm He–Cd laser beams. Asymmetrical molecular migration, which generated the blazed SR structure, was achieved by adjusting the influence of both the intensity and polarization distributions of the two beams on molecular migration.

New photo-cross-linkable liquid crystalline polymethacrylate with 4-methoxybistolane side groups was synthesized and its thermally enhanced photoinduced molecular reorientation behavior was investigated using a linearly polarized (LP) UV light. Since the bistolane mesogenic side groups were axis-selectively photoreacted under irradiating with LPUV light, annealing procedure generated the thermally enhanced molecular reorientation parallel to the polarization (E) of LP-365 nm light. The axis-selectively photoreacted bistolane moieties acted as the photo-cross-linked anchor to reorient non-photoreacted side groups along them, which direction was parallel to E. The maximum generated in-plane order parameter and birefringence were 0.43 and 0.18, respectively. The influences of degree of the photoreaction and the annealing temperature on the molecular reorientation behavior were investigated in detail. Furthermore, polarization holography using 325 nm He-Cd laser was carried out to fabricate pure polarization gratings with various polarization of the light source.

Surface relief gratings (SRG) with anisotropic gratings in photo-cross-linkable liquid crystalline (LC) polymethacrylate films comprising 4-(4-methoxycinnamoyloxy)-biphenyl (MCB) side groups were fabricated by irradiating with a linearly polarized ultraviolet (LPUV) light through a grating photomask and subsequent annealing at LC temperature range of the film. A reorientation of the mesogenic groups accompanied the molecular diffusion after the annealing, although the molecular diffusion and the reorientation direction depended on degree of the photoreaction of the mesogenic groups and the polarization (E) of LPUV light. When the degree of the photoreaction was around 7 mol%, molecules moved from illuminated area to non-illuminated area, and the molecular reorientation direction was parallel to the grating line regardless of E of LPUV light. In contrast, the diffusion direction was determined from the non-illuminated area to the illuminated region, and the molecular reorientation direction was always parallel to E of LPUV light when the degree of the photoreaction was around 20 mol%. All the fabricated SRGs showed characteristics of the polarization dependent gratings due to the surface relief formation and the molecular reorientation direction. The diffraction properties of the SRGs were good agreement with theoretical analyses.