High-performance rewritable Bragg hologram with high multiplicities

Abstract

Azobenzene-containing polymer, in which a change in birefringence can be induced by photoisomerization, is one of promising materials for holographic applications. To develop high-performance holographic materials using azobenzene polymers, it is necessary to prepare optically transparent thick films with capability of a large photoinduced change in refractive index to obtain high diffraction efficiency and fast response in the Bragg regime. A number of materials have been studied so far, but no attention has been paid to the combination of thick amorphous copolymers films containing photoresponsive and mesogenic groups in the side chain and polarization gratings formed in the Bragg regime. In this paper, we prepared optically transparent thick polymer films containing an azobenzene moiety with photosensitivity and a tolane moiety with high birefringence, and formed intensity and polarization gratings with linearly polarized beams and orthogonal circularly polarized beams, respectively. It was found that the nearly theoretically maximum diffraction efficiency was successfully achieved, and the recorded hologram could be erased thermally or photochemically. In addition, a large change in refractive index was induced in the polarization grating, and high diffraction efficiency (~90%) and quick response (920 ms) was realized simultaneously.