We are designing and developing the materials and equipment necessary to implement a sub-micrometer-scale, projection stereolithography, additive manufacturing system based on parallel two-photon polymerization with ultrashort laser pulses (see figure). A projection stereolithography system adapts three-dimensional printing for materials fabrication. Additive manufacturing generates complex three-dimensional structures by controlling the geometry and material properties of individual building blocks, and the two-photon polymerization technique enables this level of control over sub-micrometer building blocks. The technique uses a nonlinear photo-absorption process to polymerize sub-micrometer features within the interior of the resists, the light-sensitive material used to form a pattern in additive manufacturing and photolithography. After illumination of the desired structures inside the photo-resist volume and subsequent development (washing out the non-illuminated regions), the polymerized material remains in the prescribed three-dimensional form. Although it enables fabricating features on a length scale that is not possible by other additive manufacturing techniques, two-photon polymerization is currently limited to a low processing rate and a small set of materials. This prevents taking full advantage of its sub-micrometer geometric control to fabricate parts. Thus, there is a compelling need to increase the material processing rate and to develop custom two-photon polymerization resists. Technological and scientific challenges in solving these rate and material limitations arise because of the slow point-by-point serial illumination technique of the existing systems and the inability to measure and characterize the mechanical properties of additively manufactured parts fabricated with novel resists. We will address these challenges by creating a parallel process via a temporal focusing technique to perform plane-by-plane simultaneous illumination and by re-purposing micro-electromechanical system sensors to measure the mechanical properties of novel two-photon polymerization resists via direct nanometer-scale metrology of the individual building blocks.
We expect to generate the scientific knowledge, hardware, and materials to (1) fabricate millimeter-scale parts with sub-micrometer building blocks, (2) increase the rate of existing sub-micrometer additive manufacturing by at least 10 times and potentially up to 1,000 times, and (3) perform metrology-driven design of custom resists that have desirable mechanical properties. Although the underlying technologies for each of these exists separately, they have never been integrated together in the form of a functional sub-micrometer additive manufacturing system. Thus, the results of this project will fundamentally advance the state of the art in rate, resolution, and scalability of additive manufacturing. Additionally, the hardware and knowledge generated will substantially expand LLNL's existing sub-micrometer additive manufacturing capabilities for applications such as target fabrication for Livermore's National Ignition Facility and the Laboratory for Laser Energetics' OMEGA Laser in Rochester, New York. Currently, the two-photon polymerization process is being used at Livermore to fabricate OMEGA laser targets. There is an immediate need for a faster process and custom two-photon resists for this effort. In addition, this project will significantly expand the range and capabilities of hardware and resists available to the Laboratory and other users in the future. Finally, it will ensure Lawrence Livermore's continued scientific and technical leadership in the area of sub-micrometer additive manufacturing and establish collaborations with the Chinese University of Hong Kong and the University of Texas at Austin.
This project will strengthen advanced materials and manufacturing capabilities at Lawrence Livermore by generating the underlying science and technology of sub-micrometer additive manufacturing. In addition, by generating the knowledge and hardware for parallel two-photon polymerization, this work will directly support laser target fabrication efforts at LLNL relevant to current and future mission challenges in high-energy-density science and stockpile stewardship science.
In FY16 we (1) began preliminary design of the additive manufacturing system to be built at LLNL in FY17; (2) identified the specific performance metrics that are relevant to compare and evaluate the performance of the parallel two-photon process with that of the commercial, serial two-photon process; and (3) printed additively manufactured parts with new resist materials that were developed in-house at LLNL.
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