Evaluation of 3D structures fabricated with two-photon-photopolymerization by using FTIR spectroscopy

Two-photon-induced photopolymerization (2PP) has gained increased interest due to the capability of manufacturing three-dimensional structures with very high feature resolution. To assess the suitability of photopolymer systems for 2PP, methods have to be developed that allow a screening of the efficiency of monomer-initiator combinations in the context of high throughput, large processing window and geometric quality of the final parts. In this paper, a method for evaluating 2PP structures is described. For this purpose, the double-bond conversion of fabricated 2PP structures was measured giving quantifiable results about the efficiency of the photoinitiator. The method is based on local measurement of the double-bond conversion of the photopolymer using a microscope in combination with infrared spectroscopy. The obtained double-bond conversion is a measure for the efficiency of the photopolymer system (initiator in combination with monomer), and thus allows to compare different photopolymers in a quantitative way. Beside this evaluation of 2PP structures, fabrication of complex 3D structures was done to determine the limits of the 2PP technology for miscellaneous components.