Methacrylic azopolymers for holographic storage: A comparison among different polymer types

The photoinduced anisotropy and volume holographic storage in a series of polymers with different architectures and azo contents of 7% and 20% in weight have been investigated. Measurements of the birefringence (Δn) induced with linearly polarised 488 nm light show that for polymers with an azo content of 20%, the highest and more stable Δn values are achieved in copolymers with a di-block architecture. The Δn induced in polymers with 7 wt% azo content is not stable. Volume holographic polarisation gratings have been stored in the polymers. Only in the case of the di-block copolymer with an azo content of 20% in weight, the stored gratings are stable. A diffraction efficiency higher than 90% and an angular selectivity of 4° have been achieved in gratings with a period of 2 μm. It can be concluded that the di-block copolymer with 20 wt% azo content is the most suitable, among the studied copolymers, as volume holographic storage material.