Fig. 1. Technology and application of femtosecond laser 3D printing inorganic materials

Fig. 2. The basic principles of femtosecond laser 3D printing. (a) Single-photon and two-photon absorption processes; (b) Schematic diagram of single-photon and two-photon polymerization^[45]

Fig. 3. Femtosecond laser 3D printing based on organic polymer-inorganic precursor blends. (a) Illustration of the hybrid organic semiconductor photosensitive resin and its application in multiphoton lithography; (b) Fluorescence microscopy of endothelial cells cultured on bioactive and inert composite structures^[47]; (c) SEM and fluorescence images of photoluminescent CdS quantum dot structures fabricated via multiphoton polymerization^[49]; (d) SEM image showcasing tetrahedral ZnO crystals^[52]; (e) Fluorescent emission of Eu³⁺-doped ZrO₂ down-conversion spheres under 405 nm excitation^[53]; (f) Schematic of the preparation process for transparent metallic photopolymer resins^[54]; (g) Illustration of 3D microstructure synthesis in fused silica glass^[55]; (h) Ceramic composite freeform sculptures composed of silica and zirconia^[56]; (i) SEM images of micro-lenses and gratings in fused silica glass post-heat treatment at 600 ℃^[57]

Fig. 4. Femtosecond laser 3D printing utilizing organic polymer-inorganic nanoparticle composites. (a) Illustration of the Direct Laser Writing (DLW) process for fabricating 3D fused silica microcomponents from silica nanocomposites; (b) Microscopic visualization of a fused silica microlens array^[67]; (c) Diagram depicting the fabrication of 3D silica nanostructures; (d) SEM image showing amorphous glass microneedle arrays processed at 1100 ℃; (e) SEM image of a miniature ring-shaped optical resonator^[64]; (f) Schematic of a magnetic Fe₃O₄ nanoparticle-based microturbine fabricated through two-photon polymerization^[68]; (g) Fluorescence and SEM images of RGB quantum dot structures formed via two-photon polymerization^[69]; (h) Combined schematic and SEM images of printed line structures embedded with carbon nanotubes^[70]

Fig. 5. Femtosecond laser 3D printing using inorganic precursors. (a) Diagram illustrating the laser-induced reduction of metal structures, highlighting the nucleation, growth, and aggregation phases; (b) SEM image of an isolated silver pillar structure^[71]; (c) Schematic depicting the photopolymerization and laser-induced reduction of gold within a conductive photopolymer matrix; (d) SEM images of line structures fabricated under varying laser repetition rates^[72]; (e) ZnO nanostructures deposited on the surface of 3D-printed platinum lines^[73]; (f) Visualization of focal spot dimensions during the 3D printing of hydrogen silsesquioxane structures; (g) SEM image of a Fresnel lens fabricated from hydrogen silsesquioxane using 3D printing^[74]

Fig. 6. Femtosecond laser 3D printing based on inorganic nanoparticles. (a) Schematic diagram of nanoparticle assembly induced by photo-triggered polarity changes; (b) SEM image of a metamaterial cubic microstructure^[76]; (c) Illustration of the PEB printing mechanism^[77]; (d) SEM image of a silver double-helix fabricated via photopolymerization and photo-reduction^[78]; (e) Schematic of the 3D Pin printing mechanism; (f) SEM image of an Eiffel Tower model; (g) SEM images of CdSe/ZnS quantum dot left-handed (LH) and right-handed (RH) nano-helix arrays^[79]

Fig. 7. Applications of femtosecond laser 3D-printed inorganic micro/nanostructures in optical microdevices. (a) Schematic diagram of a micro-resonator fabricated using femtosecond laser; (b) 3D-printed micro-resonator cavity of lithium niobate^[80]; (c) 3D-printed optical micro-ring resonator made of molten SiO₂ glass^[81]; (d) 3D-printed micro-lens fabricated from polydimethylsiloxane^[82]; (e) 3D-printed array of micro-lenses made of SiO₂ glass^[56]; (f) 3D-printed photonic crystal made from TiO₂ woodpile structure^[83]; (g) 3D-printed photonic crystal made from ZrO₂ woodpile structure; (h) 3D-printed photonic crystal made from ZrO₂ woodpile structure with support^[84]

Fig. 8. Applications of femtosecond laser 3D-printed inorganic micro/nanostructures in MEMS sensing. (a) Polymer microbeam probe integrated at the end-face of an optical fiber, fabricated via 3D printing for precision sensing applications^[85]; (b) MEMS temperature and humidity sensor fabricated using ionic liquid-doped photopolymer through 3D printing, offering enhanced environmental sensitivity^[86]; (c) Micro-propeller flow rate sensor designed for optical fibers, 3D-printed to enable accurate fluid dynamics measurements^[87]; (d) Castle-shaped Fabry-Pérot interferometer (FPI) microcavity optical fiber humidity sensor produced via 3D printing, offering high accuracy in humidity detection^[88]; (e) Metamaterial cantilever optical fiber end-face micro-force probe fabricated by 3D printing for detecting minute forces with high resolution^[89]; (f) Optical fiber refractive index sensor incorporating a 3D helical grating cone structure, enabling precise liquid refractive index measurements^[90]; (g) Optical fiber acoustic wave sensor with a 3D-printed micro-spring support and thin-film design, optimized for enhanced acoustic signal detection^[91]

Fig. 9. Applications of femtosecond laser 3D-printed inorganic micro/nanostructures in life sciences. (a) Diagram illustrating the role of 3D-printed components in the manipulation of humanoid robots for biomedical applications^[92]; (b) Schematic showing the fabrication of micro-robots using a combination of two-photon polymerization and sintering, enabling robust and functional designs; (c) Pure nickel helical micro-robot fabricated via 3D printing, utilizing magnetic actuation for precise control in biomedical environments; (d) Illustration of magnetic-driven micro-robots performing controlled swimming within a microfluidic chip containing flowing liquids, demonstrating potential in targeted delivery applications^[93]; (e) Model and sintering process of porous ceramic scaffolds fabricated by 3D printing, designed for high-temperature applications and potential use in tissue engineering^[95]