Modeling of two-photon polymerization in the strong-pulse regime

摘要

This paper reports a study of two-photon polymerization induced by femtosecond laser pulses having microjoule pulse energy and kilohertz repetition rates. Light-matter interaction and polymerization kinetics are modeled in highly confined spatiotemporal scales. The model employs a non-diffractive Bessel beam, considers the effects of temperature-dependent species diffusions, and regards propagation and termination kinetic constants as functions of double-bond conversion. The model is validated by comparing the size of features predicted from simulations to those generated experimentally. The model is used to investigate how the time and energy required to create a single volume element ("voxel") change under various conditions of irradiation. The results show that polymerizing a single voxel requires a minimum exposure time that is constant across a range of irradiation conditions, and is largely determined by the chemical kinetics. In the regime where the pulse energy is low (< 10 μJ), it is more energy-efficient to use fewer pulses having higher energy within the same total exposure time. However, this trend reverses in the regime where the pulse energy is high (10μJ-30 μJ), because radical-radical recombination becomes significant, which wastes absorbed energy. This work advances the understanding of two-photon polymerization in the strong-pulse regime and is a step toward increasing throughput to a level suitable for industrial applications.