Azobenzene-containing polymers have attracted much attention as photo-responsive materials owing to potential applications in optical data storage and holographic recording. In holography, azobenzene compounds doped in a polymer matrix (guest- host polymer film) or chemically attached to the polymer (co-polymer) are among the most widely used materials. Azo-polymers exhibit differing behaviors when exposed to a pattern resulting from the interference of two coherent beams. In the guest-host system, the recorded grating corresponds to a contrast of refractive index between the dark and bright areas of the film, and in the co-polymer, interference patterns lead to surface height modulation; i.e. surface relief gratings (SRGs). The latter is due to photo-induced mass movement of the polymer from bright to the dark area of the interference pattern in the direction of the intensity gradient, and the photoisomerization force is at the origin of the formation of the gratings. In this paper, we give an overview of our experiments on holographic recording in both guest host and co-polymers systems; e.g. doped and covalently attached polymers, and based on the theory of photo-induced vectorial mobility of matter, we discuss the results obtained for the co-polymer system.
Over the past two decades, surface relief gratings have attracted much interest owing to their potential applications in optical data storage and optical communication and holography. Azobenzene-containing polymer films show an interesting behavior under irradiation with light interference patterns. The inhomogeneous irradiation; e.g. due to the interference pattern, of the azo-polymer film causes mass movement of the polymer from bright to dark area, and the mechanism underlying the formation of SRG finds its origin in the photoisomerization force. The latter is due to an inhomogeneous light irradiation which causes photoisomerization and increases the polymer mobility in the bright area, and owing to the intensity gradient, due to light interference, the photoisomerization force moves the polymer from the bright area into the dark. In this paper we discuss our experiments of holographic recording in films of Poly (Disperse Red 1 methacrylate); e.g. azo-polymer films, and the recorded surface relief gratings were investigated by using atomic force microscopy. The dependence of the polarization state and intensity of the writing beams was studied, and the diffraction efficiency was monitored in real time during the process of inscription. A brief description of the photoisomerization force is given.