Azobenzene‐containing liquid crystalline poly(methacrylates) with different spacer length as media for holographic grating recording

Abstract

Liquid crystalline (LC) poly(methacrylates) with azobenzene moieties in their side chains have been synthesized and their chemical structure has been confirmed with nuclear magnetic resonance spectroscopy and gel permeation chromatography. Azobenzene moieties are linked to polymer backbone via an alkyl spacer with length from 2 to 10 methylene units. Photooptical processes in thin amorphized polymer films are examined through measurements of optical anisotropy and holographic grating recording. Birefringence values induced with a linearly polarized green (532 nm) laser beam has strongly depended from the spacer length. Irradiation with two circularly polarized green laser beams leads to the formation of polarization and surface relief gratings, which have been visualized with polarized optical and atomic force microscopy, respectively. Diffraction efficiency of the recorded gratings is in correlation with the spacer length, namely, the shorter the spacer, the higher diffraction efficiency can be achieved. For polymers with short spacers polarization gratings can be easily erased by circularly polarized light, but only partial erasing of surface relief gratings is observed. The results presented offer the possibility of tailoring the chemical structure of azobenzene‐containing polymers for designing high‐efficiency media for the holographic recording.