High-aspect 3D two-photon polymerization structuring with widened objective working range (WOW-2PP)

We developed a novel two-photon polymerization (2PP) configuration for fabrication of high-aspect three-dimensional (3D) structures, with an overall height larger than working distance of the microscope objective used for laser beam focusing into a photosensitive material. This method is based on a modified optical 2PP setup, where a microscope objective (100× high N.A.), immersion oil and cover glass can be moved together into the photosensitive material, resulting in an effective higher and wider objective working range (WOW-2PP). The proposed technique enables the fabrication of high-aspect structures with sub-micrometer process resolution. 3D structures with a height of 7 mm are demonstrated, which could hardly be built with the conventional 2PP set-up due to refractive index mismatch and laser beam disturbances. Researchers have used two-photon polymerization to fabricate tall and intricate structures with submicrometre resolution. Two-photon polymerization is a popular scheme whereby a focused laser beam polymerizes a photosensitive liquid to create three-dimensional objects. However, structures fabricated using this technique are usually limited in height by the working distance of the microscope lens used to focus the laser into the sample. Boris Chichkov and co-workers from the Laser Zentrum Hannover in Germany have now adapted two-photon polymerization with a vertical motion system that allows the microscope objective and its protective cover glass to be moved down into the reservoir of the liquid photoresist. As a result, they were able to fabricate a variety of high-aspect-ratio structures, including tubes, funnels, hour-glass shapes and a miniature model of the Tokyo SkyTree.