Two-photon absorption induced photopolymerization

Organic two-photon chromophores undergo a process called two-photon absorption in which light is absorbed in the infrared wavelength range, which in turn can initiate photochemistry using either the two-photon excited molecule or its up-converted fluorescence emission. One type of photochemistry for which the two-photon up-conversion can be used is photopolymerization. Organic/polymeric materials often exhibit non-resonant linear absorption in the ultraviolet (uv) wavelength range, while in near infrared (NIR,) wavelengths little or no absorption is observed. As a result NIR light can penetrate much deeper into the organic materials to initiate photocuring throughout the resin. Thus, using this NIR photocure technique, it is possible to photocure objects thicker than those fabricated with traditional ultraviolet curing. Novel two-photon organic chromophores developed in the Air Force Research Laboratory (AFRL) and by other research groups exhibit large effective two-photon cross-section values, which provide efficient excited molecular states or localized uv/visible fluorescence required for photocure. The utilization of up-conversion photochemical processing provides a relatively new processing method for fabrication of structures ranging from precisely patterned nanostructures to thick structures (>1cm). This research evaluates the advantages and limitations of this new polymer processing technique and the critical factors influencing the reaction.