Tunable Nonlinear Optical Pattern Formation and Microstructure in Cross-Linking Acrylate Systems during Free-Radical Polymerization

Abstract

We report cross-link-tunable, nonlinear optical pattern formation of transmitted light in a photopolymer undergoing free-radical polymerization. Photopolymerization induces microscale filamentation of a uniform, broad transmitted beam, which corresponds to a concurrent spatial evolution in cross-linked morphology in the photopolymer. Because the photopolymerization is permanent, the ensemble of filaments imprint a microstructure comprising a cross-link gradient pattern. Tuning the system’s capability to cross-link and branch changes the magnitude of the refractive index change (Δn), which both induces nonlinear conditions and also changes the strength of the optical nonlinearity. Only a monomer with sufficient functionality shows stable optical pattern formation, and its nonlinear regime exists for a specific range of exposure intensities. A monomer of lower functionality can be pushed into the nonlinear regime by formulating it with higher functional monomers, whereby Δn is increased to provide a stronge...