Accurate Morphology-Related Diffraction Behavior of Light-Induced Surface Relief Gratings on Azopolymers

Holographic relief gratings can be fabricated directly on the surface of azobenzene-containing materials (or simply azomaterials) without additional development steps. Despite often being described to have ideal sinusoidal profiles, the developing surface morphology in large amplitude gratings can affect the light distribution of the writing interferogram, causing profile deformations and deviations in the expected diffraction behavior. In this work, we characterize the temporal evolution of the surface relief grating (SRG) morphology fabricated by means of interference lithography on azopolymer films, quantitatively relating the results of a Fourier analysis of their surface profiles to the accurate measurement of efficiencies in the transmitted diffraction orders. A reliable surface structuration dynamics is empirically extracted from the analysis and used to formulate a simple but detailed diffraction model that, within the scalar diffraction theory, exhaustively describes the diffraction behavior of real SRGs without the need of complex rigorous electromagnetic theories. Our results add a deeper insight in the quantitative description of the morphology and the diffraction behavior of SRGs, which can contribute to their adoption for operating high-performance, reconfigurable, compact, and lightweight diffractive optical devices.