Laser induced optically and thermally reversible birefringence in azopolymers

Azopolymers are well known organic materials for polarization holographic recording due to the induced anisotropy under illumination with polarized light. They possess all the desirable characteristics of the known polarization- sensitive materials, as high sensitivity and reversibility, but excel them substantially in the magnitude of the photoinduced birefringence. This makes possible to record reversible polarization gratings with high diffraction efficiency. In this paper results of experimental investigations on the reversibility properties of birefringence photoinduced in azopolymers are reported, depending on the conditions of subsequent optical and thermal treatment. Thin films of different polymers were prepared in order to examine the kinetics of multiple recording and erasure of birefringence in different types of azopolymers. The reversibility of the polarization recording has been studied using two different method of erasure - by increased temperature and on illumination with circularly polarized light.