Figure 2.

(a) Schematic of the two photon polymerization process. The energy distribution is a Gaussian shape. The radius of the polymerization voxel corresponds to the position at which the energy intensity exceeds the excitation threshold of the photoinitiator. (b) Single photon versus two photon polymerization. Single photon polymerization is limited to the surface of a given material. On the other hand, two photon polymerization may occur within a given material. (c) Schematic of the rapid prototyping process. In the first step, a computer-aided design program is used to prepare a STL format file. The STL format file is subsequently used to prepare a layer-by-layer contour of the structure. The structure is fabricated by rastering the laser in order to fill the area contained within the contours.