Approaches to Minimizing Limitations Inherent to the Two-Photon Printing Process

A unique but impactful application for two-photon printing that emerged in recent years is to print millimeter-scale polymeric components for nuclear fusion experiments. While turnkey two-photon printers such as Nanoscribe’s PPGT+ are extremely sophisticated and capable, this application requires print fidelity at the limits of what is possible with available software and resins. Inherent properties of greatest concern are the roughness of printed structures, particularly at stitching interfaces, and waviness of thin curved surfaces that result from shrinkage-induced stresses. Challenging designs of interest include high-surface-area lattices with sub-micron features and high-aspect-ratio structures. These designs are too complicated to be constructed with geometric modeling kernels so a field-driven algorithm that is more suited for modeling complex lattice geometries was used. Resulting structures processed in a traditional way possess unacceptably large stitching features (&gt;1µm peak-to-valley) and an undulating profile with nodes at print block interfaces.<br/><br/>Strategies to mitigate these issues include using third-party software such as nTop to better control the size, print sequence, and mesh quality of individual print blocks; scripts to batch process thousands of image files into a 2.5D lithographic-type print; direct coding an analytical expression to print the structure, forgoing the need to process a CAD model; and the development of low-shrinkage resins using base-catalyzed rather than free-radical chemistry. Examples of structures with improved quality that can be made using these methods include thin-wall spherical shells, hemi-shells, planar foils, and stochastic lattices with features &lt; 0.5µm. Print processes were qualified and components characterized using a suite of techniques including optical, confocal, atomic force, x-ray, and scanning electron microscopy. In this talk, the methods and representative prints will be discussed in greater detail, along with recommendations that may prove beneficial for others using first generation two-photon printers.<br/><br/>This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number DE-NA0004144.