Two-Photon Polymerization: A New Approach to Micromachining

ment of ultrashort laser systems is creating exciting possibilities for very precise localization of laser energy in time and space. These achievements have triggered novel laser applications based on nonlinear interaction processes. A promising three-dimensional microfabrication method that has recently attracted considerable attention is based on twophoton polymerization with ultrashort laser pulses.1-5 When focused into the volume of a photosensitive material (or photoresist), the pulses initiate two-photon polymerization via two-photon absorption and subsequent polymerization. After illumination of the desired structures inside the photoresist volume and subsequent development — e.g., washing out the nonilluminated regions — the polymerized material remains in the prescribed 3-D form. This allows fabrication of any computer-generated 3-D structure by direct laser “recording” into the volume of a photosensitive material (Figure 1). Because of the threshold behavior and nonlinear nature of the process, a resolution beyond the diffraction limit can be realized by controlling the laser pulse energy and the number of applied pulses. As a result, the technique provides much better structural resolution and quality than the