Single-Step 3D Printing of Micro-Optics with Adjustable Refractive Index by Ultrafast Laser Nanolithography

Laser exposure defines voxel's dimensions as essential building blocks in direct write 3D nanolithography. However, the exposure conditions not only influence the size of the produced features but also their optical properties. This empowers the realization of an adjustable refractive index out of single material by varying the writing strategy while preserving laser 3D nanolithography's flexibility in geometry and high resolution. Here, the refractive index for the 450–1600 nm spectral range of the micro-optics out of SZ2080 hybrid polymer is systematically studied by applying ray and wave optics approaches followed by optical resolution analysis. It reveals the exact value of the laser-printed components instead of the determination assessed by other techniques measuring thin films or bulky volumes of the investigated substance. The studied micro-lenses are of below 100 µm in dimensions and a clear distinction in their performance on low and high exposure doses is found by analyzing it in all different approaches and validating using different lithography setups. Findings reveal the complexity of the refractive index of the 3D micro-optics which is influenced by the material density and morphology. A route for freedom in 3D printing shape and refractive index can be realized by the technological optimization of delicate exposure control in ultrafast laser nanolithography.