Thermally sensitized optical recording in azobenzene polymers

Optical storage in azobenzene-containing polymers is based on the alignment of the polymer chains initiated by the reorientation and ordering of the azobenzene groups. This process requires considerably high recording energies. We investigate photoinduced birefringence in two types of acrylic cyan-azo polymers - one amorphous and one liquid crystalline. We show that for both types the light energy required for the recording can be reduced by an order of magnitude if the photoalignment is done at elevated temperatures. The optimal temperatures depend on the polymer. In our case they are 52-55°C for the liquid-crystalline polymer and 50-60°C for the amorphous polymer. At these temperatures birefringence as high as 0.07 can be obtained at light intensities 30-40mW/cm2 for about 100s and these values are retained after cooling the polymer films.