Photoaddressable polymers for optical storage

The design of the macromolecular architecture and the specific properties of the photo addressable unit are subject of high interest in the development of functional materials for optical applications, in particular for optical storage. One of the research lines in our group concerns photo-adressable polymers for holographic storage. Our work is centred in the photo induction of anisotropy and holographic gratings recording in azo containing polymeric thin films.

Upon polarized irradiation, the azo containing polymers experience molecular reorientations giving rise to changes of their optical properties. The photoinduced changes are reversible, so these materials can be recorded and erased many times (as rewritable CD). The optimization of the recording conditions, both in homopolymers and copolymers, under continuous laser excitation has been one of our objectives.The search of materials with low absorption and scattering levels but in which the mesogenic photochromic groups are confined in nanoscopic regions lead us to the study of block copolymers. Actually, block copolymers have much higher optical anisotropies than the corresponding random copolymers with the same azo content being confirmed the effect of azo confinement.

The interest of fast recording has led us to extend our studies to pulsed excitation. Stable optical anisotropy and holographic ( both anisotropy and surface) gratings have been induced with a single 532 nm and 4 ns light pulse.