Femtosecond two-photon stereo-lithography

We report herein a method for the three-dimensional (3D) fabrication of mic rostructures by means of direct fs-beam writing (scanning) inside a polymer izable resin. Photopolymerization takes place via two-photon absorption (TP A), as indicated by measurements of transmission power dependence. This con cept of fabrication is based on two principles: the use of short, sub-picos econd 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 thre shold. Under such conditions, no filament formation takes place and no ther mal convection disturbance occurs in the focal vicinity during photo-polyme rization. This technique requires no sacrificial layers or structures in re al 3D micro-stereo-lithography.