Optical erasures and unusual surface reliefs of holographic gratings inscribed on thin films of an azobenzene functionalized polymer

摘要

The optical erasing of holographic gratings inscribed on azobenzene homopolymer thin films of p(DR1M) is analyzed for various polarizations of the erasing single beam. Gratings of different diffraction efficiencies are first inscribed using different states of the incident interfering beams, either linearly polarized in the plane of incidence-horizontal direction (p+p)-or linearly polarized at +-45 deg with respect to the vertical (s) direction (+45 deg, -45 deg), or even Right and Left circularly polarized (RCP+LCP), respectively. A single beam of "s", "RCP" or "p" polarization is then used for optical erasure and the variations in the diffraction efficiencies, as measured on the intensity of the diffracted first order S_(+1), are monitored over short and long time periods. In addition, changes in the amplitude of the sinusoidal surface relief modulations are checked by atomic force microscopy (AFM) measurements and, in some cases, complex profiles with new modulations parallel and/or perpendicular to the grating vector direction are evidenced for the first time. Finally, kinetics of the various erasing processes are compared and discussed in connection with the more probable constructive interference mechanisms which could take place between the transmitted and diffracted beams. A model for a real retroactive effect is suggested and the necessary conditions to fulfil for using these gratings in phase mask applications are discussed.