Temporal analysis of grating formation in photopolymer using the nonlocal polymerization-driven diffusion model

TLDR

The nonlocal polymerization‑driven diffusion model (NPDD) predicts high spatial‑frequency cut‑offs and higher‑order grating components in photopolymers. The study proposes extending NPDD to include the temporal response of polymer chain growth. The extended model adds an exponential transient response, is solved by finite‑element analysis, and its predictions of refractive‑index modulation, diffraction efficiency, and material parameters are validated against experimental data using rigorous coupled‑wave theory.

Abstract

The nonlocal polymerization-driven diffusion model (NPDD) has been shown to predict high spatial frequency cut-off in photopolymers and to accurately predict higher order grating components. We propose an extension to the NPDD model to account for the temporal response associated with polymer chain growth. An exponential response function is proposed to describe transient effects during the polymerization process. The extended model is then solved using a finite element technique and the nature of grating evolution examined in the case when illumination is stopped prior to the saturation of the grating recording process. Based on independently determined refractive index measurements we determine the temporal evolution of the refractive index modulation and the resulting diffraction efficiency using rigorous coupled wave theory. Material parameters are then extracted based on fits to experimental data for nonlinear and both ideal and non-ideal kinetic models.