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Finer Features for Functional Microdevices



Device miniaturization and multifunctionalization are important issues in nano-research fields. A high fabrication accuracy can be reached by conventional UV lithography and by focused particle-beam drilling, but they are in nature planar processing methods and therefore not suitable for creating three-dimensional (3D) devices. To solve this problem, we proposed a femtosecond laser two-photon photopolymerization method, which uses photopolymers of versatile functions, is easy to operate, and has intrinsic 3D processing capability [1-4].

The basic idea of two-photon photopolymerization is tightly focusing femtosecond laser into a photopolymerizable resin, which is of liquid status. Photopolymerization reactions is triggered at the center of the focal spot by photo-generated radicals or cationic by simultaneously absorbing two red photons, through which, resin is locally converted to solid state. The use of two-photon absorption enables laser-beam deep penetration into materials and higher spatial resolutions, both critical for 3D fabrications. Complicated structures are formed by translating the focal spot according to preprogrammed CAD patterns. After the laser scanning, the sample was developed by washing out unsolidified liquid, and the solid skeleton remains. The processes are shown in Fig. 1. It is due to two-photon absorption, near-infrared wavelength (780 nm, 150 fs) was used so that laser penetrated deep into materials


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