Evidence for photoinduced molecular migration mediated surface-relief grating formation in azo-dye polymers

Direct and reversible holographic recording of surface-relief gratings in a te-dye polymers was recently evidenced using atomic force microscopy. Irrad iation with an interference pat trm between polarized laser beams was obser ved to lead to quantitative mass-transport. The surface gratings have a neg ative amplitude that can be twice as large as the polymer film thickness, T he origin of such photo-driven mass transport is still controversial. We pr ovide here experimental evidence that the chromophores migrate from the hig h to low the intensity regions. Chain migration in such doped or grafted gu est-host polymer systems results from the photoinduced migration of the gue st chromophores.