Multistage Networks for Glassy Holographic Photopolymers

In the writing of holographic photopolymers, the addition of a third-stage cure to the typical polyurethane matrix and acrylate writing monomer steps is used here to modify the ultimate thermomechanical properties of the final holographic photopolymer. Inclusion of a thermally latent, low-refractive-index epoxide homopolymerization increases the T_g from a value of −22 °C during the writing step to a final T_g of 101 °C after the epoxide cure. Critically, the diffraction grating structure is retained with high fidelity, an index contrast of 0.0057, and a diffraction efficiency of 89% achieved in these materials. Ultimately, the 3-stage design and final glassy nature of these materials promote thermal and dimensional stability of the final holographic material.