Polarization Dependent Holographic Write, Read and Erasure of Surface Relief Gratings on Azopolymer Films

Surface relief grating (SRG) fabrication on azobenzene functionalized polymer films is investigated under different polarization combinations for the two writing beams. The grating formation was sequentially monitored with orthogonally polarized read beams and the surface topography by atomic force microscope. The SRG formation on amorphous azopolymer films is found to depend on the spatial variation of the intensity as well as the magnitude and direction of the interference field pattern. The treatment presented in this article defines the intensity and polarization distribution across the two-beam interference region for different polarization combinations of the interfering beams. Efficient photoisomerization and reorientation processes due to the spatial variation of the optical field results in a bulk birefringence grating (BG). Simultaneous presence of a component of electric field gradient in the grating vector direction results in a large modulation depth SRG. The effects due to the simultaneous formation of BG and SRG are studied by probing the grating formation process with vertical (V-) and horizontal (H-) polarized read beams. Our experimental results suggest that, under appropriate writing conditions and observation time scales, the V- polarized read beam probes predominantly the BG while the H- polarized read beam gets diffracted predominantly by the SRG. The experimental results are analyzed based on the resultant electric field pattern produced due to interference of polarized light beams. We have also investigated the unusual optical and thermal erasure properties of the photofabricated SRGs.