We investigated formation of holographic gratings in the isotropic phase of polymer azobenzene liquid crystals (PALCs)o On irradiation of interfering light at 488 nm (writing beams), a first-order diffraction light of readout beam operating at 633 nm was immediately observed even though PALCs exhibited optically isotropic state. Diffraction efficiency depended on the polarization direction of the writing beams. When linearly polarized beams were employed for the writing beams, the highest diffraction efficiency was obtained. Polarized absorption spectra of PALC films showed the alignment change of the azobenzene moieties by irradiation of the linearly polarized light at 488 nm, in which the azobenzene moieties aligned perpendicular with respect to the polarization direction of the light. Therefore, it was speculated that photoinduced alignment of azobenzene moieties was caused in bright regions of interference pattern. Rise and decay times of the diffraction signal were evaluated as approximately 400 and 300 ms, respectively. Furthermore, the grating formation could be controlled repeatedly by turning on and off the writing beams.
