Highly efficient formation of holographic gratings in polymer liquid crystals

摘要

We studied the formation of gratings by means of the photoinduced alignment change of polymer liquid crystals (PLCs) in a glassy state. To obtain high diffraction efficiency (η), we prepared a novel PLC containing an azobenzene group directly connected with a tolane moiety (3AT) which has large birefringence (Δn). It was found that the value of birefringence in 3AT was extremely high (Δn = 0.39). When two s-polarized writing beams (Ar~+ laser, 488 nm) were interfered on the surface of the 3AT film in the glassy state, multiple diffraction beams were observed immediately, resulting from the grating formation. We explored the effect of light intensity on the grating formation and the relation between the alignment change and η. The value of η showed a maximum when the change in photoinduced alignment was almost completed. Furthermore the value of η was relatively high (η = 20%) even though the alignment change of mesogens was small.