Image storage through gray-scale encoding of second harmonic signals in azo-dye copolymers

The authors investigated the optical data and image storage in polymeric materials functionalized with azo-dye molecules. Thin films are initially poled to generate a spatially homogeneous second harmonic signal. The information is locally inscribed through the disorientation of the azo chromophores by successive isomerization cycles induced through the two-photon absorption processes. The resulting micron-scale controlled decrease in second harmonic signal can be exploited to perform optical storage. As a demonstration of the proposed method, they store a picture with an 8bit gray-scale encoding. This image can only be retrieved through second harmonic detection and not by linear optical imaging techniques.