A schematic explaining multiphoton lithography. A focused ultrafast laser beam can induce localized multiphoton absorption inside a transparent material at its focal point, while leaving all other parts of the material unaltered. The affected zone can be as small as 10s to 100s of nanometers. If applied to photoresists, i.e., materials that can be patterned by photon absorption-induced modifications and the subsequent development process (typically chemical etching), 3D printing with nanoscale resolution can be achieved by tracing out wanted 3D shapes in the photoresist using the laser focal point. 

3D-printed silica glass structures using MPL and HSQ. The leftmost figure shows the world’s smallest wineglass made of silica glass that we printed on a chip. The cantilever shows the capability of our approach in fabricating suspended glass structures with sub-micrometer resolution in all dimensions. What is special about our approach is that no postprocessing is involved, and the as-printed glass is solid and transparent. This is a crucial advantage for its seamless integration with integrated microsystems. [Huang, P.-H., et al. Nature Communications 14.1 (2023): 3305., https://doi.org/10.1038/s41467-023-38996-3] 

3D printing of hierarchical Si-rich glass structures by simultaneous crosslinking of HSQ and ultrafast laser-induced formation of self-organized nanogratings. The left figure shows that the orientation of the nanogratings can be controlled by the laser polarization. The right figure demonstrates the capability of this approach in printing suspended structures with various orientations. What is special about this approach is that the nanogratings are self-formed within the laser focal zone, enabling fast generation of hierarchical structures within the 3D-printed architectures that can provide a large surface area and defined porosity. [Huang, P.-H., et al. ACS nano 18.43 (2024): 29748-29759., https://doi.org/10.1021/acsnano.4c09339]