Control of optical nano-structure of azo-benzene polymers and its application to diffractive optics

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Surface relief holograms are fabricated by means of irradiation of laser interference patterns. The diffraction efficiency and the surface relief depth depend on the writing energy and the polarization of the writing laser beam. This structure is very stable at temperatures under glass transition temperature T_g. We proposed a new technique to control the surface relief structure. The electric charge was deposited on the surface relief grating in a corona-depositing poling setup in an oven. The first-order diffraction efficiency measured before and after corona discharge increased from about 0.24 % to about 28 %. This diffraction efficiency increase is mainly caused by the increase of the relief depth caused by the electric charge. The relief depth is increased from 20 nm to 350 nm by corona charging.The formation and erasure of photoinduced surface relief gratings (SRGs) on azobenzene-containing polymers are simulated using a calculation model based on the moving-particle semi-implicit (MPS) method. For the convection calculation, an anisotropic diffusion model is proposed. The gradient force of the optical electric field and the influence of surface tension are considered as driving forces for photoinduced mass transport. The viscosity of polymer films changes with the light intensity in our model. Particle motions in SRG formation and erasure are calculated and the SRG pitch and polarization dependences of the SRG growing and erasing rates are investigated. These theoretical results coincide qualitatively with our experimental results.