Femtosecond two-photon stereo-lithography

We report herein a method for the three-dimensional (3D) fabrication of microstructures by means of direct fs-beam writing (scanning) inside a polymerizable resin. Photopolymerization takes place via two-photon absorption (TPA), as indicated by measurements of transmission power dependence. This concept of fabrication is based on two principles: the use of short, sub-picosecond pulses and simultaneous tight focusing (numerical aperture, NA > 1). This approach creates a unique opportunity for avoiding self-focusing even at very high intensities, as the power is lower than the self-focusing threshold. Under such conditions, no filament formation takes place and no thermal convection disturbance occurs in the focal vicinity during photo-polymerization. This technique requires no sacrificial layers or structures in real 3D micro-stereo-lithography.