Photocrosslinked surface relief gratings on azobenzene-containing copolymer films

An amorphous polymer containing Disperse Red 1 (DR1) and crosslinkable acrylic groups as separate side groups was synthesized. Surface relief gratings were optically inscribed onto films of this polymer. Grating depths of 350 nm were obtained after 40 min of irradiation. The first-order diffraction was monitored during the laser irradiation, and an efficiency of about 22% was achieved. The polymer could be photocrosslinked at 80 °C under UV light. Although some photo-degradation due to UV irradiation of the azo chromophores was observed, the surface relief itself was fixed by the photocrosslinking, as observed by the improved thermal stability of the diffraction efficiency. Even after heating above the glass transition temperature (Tg) for 2.0 h, significant diffraction was still present and the grating was still observed. In comparison with the photocrosslinked gratings, a non-crosslinked grating rapidly lost most of its shape when heated above Tg. Thus, photocrosslinking is a useful method to improve the thermal stability of the gratings.