| Popis: |
Two-photon induced photopolymerization allows fabrication of complex three-dimensional structures with sub-micron resolution in a single exposure/development cycle. We analyze the kinetics of two-photon polymerization in multi-functional acrylic photopolymers and SU-8 epoxy resins as a function of two-photon photosensitizer and electron acceptor concentrations. The rate of polymerization is observed to be directly proportional to the concentration of the two-photon photosensitizer, directly proportional to the square of the intensity, and varies more weakly with the concentration of electron acceptor. A transition from high aspect ratio to low aspect ratio structures is observed that depends on both the energy absorbed per unit area and the concentration of the photoinitiator system. In acrylates, quantitative estimates of the photoinitiation rates suggest that the concentration of radicals at threshold is much higher under two-photon exposure conditions than under one-photon exposure conditions. Diffusion of radicals or inhibitors into or out of the illuminated region may have important effects on the overall reaction rate for two-photon induced polymerization. |
