High dynamic range two-stage photopolymer materials through enhanced solubility high-refractive index writing monomers

Holographic photopolymers capable of high refractive index modulations (Delta n) on the order of 10(-2) are integral for the fabrication of functional holographic optical elements (HOEs) for use in a range of optical applications. A novel high refractive index liquid writing monomer suitable for two-stage photopolymer systems was designed and synthesized. This monomer exhibits facile synthetic procedure, low viscosity, high refractive index as well as excellent solubility in a low refractive index urethane matrix. The solubility limit, refractive index change and reaction kinetics/conversion were studied against a commercial reference high refractive index monomer, 2,4,6-tribromophenyl acrylate (TBPA). Superior performance in solubility to TBPA is shown with similar reaction kinetics and final conversion as confirmed by real-time Fourier transform infrared spectroscopy (FTIR) and real-time monitoring of diffraction grating growth. We demonstrate the ability to load substantial amounts of these writing monomers enabling a straightforward path to higher achievable Delta n values (peak-to-mean Delta n similar to 0.03) without sacrificing optical properties (transparency, color or scatter) as validated through recording similar to 100% efficiency volume transmission holograms in sub-15 mu m thick films.