Micro-fabrication using two-photon absorption by femtosecond laser

Abstract

As a femtosecond laser has recently been developed, both of high power and high photon density are easily obtained. The ultra violet or blue laser light is used for photopolymerization of urethane acrylate resin of which absorption spectrum is from 350nm to 420nm shorter than the wavelength of the femtosecond laser. The strong intensity laser light highly localized in focal region, however, can make polymerization owing to the nonlinear effect, so called, the two-photon absorption (TPA). The stereo-lithography using the two-photon absorption makes micro structures of several hundred nanometer sized block, called voxel, with great resolution. We have used this phenomenon to make micron-sized structures with sub-micron resolution. Before the fabrication, optical setting, data design and computer controlled fabrication process has been tested and developed. Voxel size has been measured along as exposure time for definite laser output power. With the processing method and voxel size data, precise 2-D structure fabrications have been performed. Furthermore the TPA photopolymerization is applied to poly-dimethyl siloxane (PDMS) molding as an application. In this paper, we report the recent progress and application of this technology in our laboratory.