Fabrication of opaque and transparent 3D structures using a single material via two-photon polymerisation lithography

Two-photon polymerisation lithography enables the three-dimensional (3D)-printing of high-resolution micronand nano-scale structures. Structures that are 3D-printed using proprietary resins are transparent and are suitable as optical components. However, achieving a mix of opaque and transparent structures in a single optical component is challenging and requires multiple material systems or the manual introduction of ink after fabrication. In this study, we investigated an overexposure printing process for laser decomposition, which typically produces uncontrollable and random 'burnt' structures. Specifically, we present a printing strategy to control this decomposition process, realising the on-demand printing of opaque or transparent structures in a single lithographic step using a single resin. Using this method, opaque structures can be printed with a minimum feature size of approximately 10 mu m, which exhibit <15% transmittance at a thickness of approximately 30 mu m. We applied this process to print an opaque aperture integrated with a transparent lens to demonstrate an improved imaging contrast.