Photo-initiator free two-photon polymerization using nonlinear deep-UV excitation

Abstract

Two-photon polymerization (TPP) enables us to fabricate three-dimensional structures with feature sizes beyond the diffraction limit. In TPP, since near-infrared femtosecond pulsed laser has been used for two-photon excitation, photo-initiators are added into a resin to trigger the TPP reaction. Here, we propose a photo-initiator free TPP by utilizing monomer’s intrinsic absorption in the deep-UV (DUV) region. Chemical bonds in monomer molecules are directly two-photon-excited with a visible femtosecond pulsed laser at 400-nm wavelength. We fabricated 3D nano-structures of acrylic oligomer, inorganic materials, and biomaterials without a photo-initiator. Raman spectroscopy study clarified chemical structure changes upon DUV two-photon excitation.