A detailed investigation of the polarization-dependent surface-relief-grating formation process on azo polymer films

We have carried out two-beam interference experiments to form surface-relie f gratings (SRGs) on azo polymer films under different polarization combina tions. The mechanism of SRG formation on azobenzene chromophore functionali zed polymer films has been shown to depend on both the spatial variation of the intensity as well as the polarization state of the incident field patt ern. The treatment presented in this paper clearly defines the intensity an d polarization distribution across the two-beam interference region for dif ferent polarization configurations of the interfering beams. The efficient photoisomerization process due to the spatial variation of the optical fiel d renders the material anisotropic and the surface mobile. The simultaneous presence of a component of electric held gradient in the grating vector di rection results in large-modulation-depth SRGs. We have carried out this in vestigation in one class of prototypical amorphous epo ty-based azo polymer thin films. Our results confirm that efficient SRG formation on azo functi onalized polymer film requires photoinduced anisotropy and a component of o ptical field gradient in the direction of the grating vector.