The Voxel Onset Time as a Method for the Evaluation of Two Photon Lithography

Two photon lithography allows the fabrication of arbitrary 3D structures with possible applications as micromechanical and microelectromechanical systems, photonic devices, 3D cell culture systems and scaffolds for tissue engineering. In order to achieve maximum resolution the process parameters have to be perfectly fitted to a given material. Normally, this interaction is studied by measuring the size of the generated volume pixels (voxel). In general, these analyses are time consuming, since they necessitate careful sample preparation and the use of a scanning electron microscope. In this paper, the threshold time for voxel formation, the voxel onset time (VOT), is presented as a parameter, which can give additional insight in the process of voxel formation. VOT is measured by a simple optical method, which can be implemented easily in already existing two photon lithography setups. Since the VOT method is considerably faster than voxel size analysis, it could be used in the future for faster screening of novel materials, while giving additional input of time dependencies of voxel growth.