Birefringence grating and surface relief grating on an azo polymer

Two types of photo-induced gratings, birefringence and surface relief gratings, were formed on an azo polymer film when two orthogonal circularly polarized writing beams irradiated the film. The relief height inscribed on the surface was measured by using atomic force microscope, and the diffraction efficiencies of all the diffracted orders were measured simultaneously. The transmitted beam intensities were calculated using a Jones matrix for the two gratings. The phase differences for the two gratings were separately determined by fitting the experimental results to the theory. Diffraction efficiency, measurement and analysis revealed that the two gratings were independent of each other and that the mechanisms for the two gratings were different.