Fig. 1. Different femtosecond laser processing techniques. (a) Femtosecond laser direct writing processing^[24]; (b) etch-assisted femtosecond laser processing^[25]; (c) femtosecond laser interference processing^[26]; (d) optical field modulated femtosecond laser processing^[27]

Fig. 2. Silicon microlens arrays and integrated preparation of microlenses on silicon cantilever beams^[34]. (a) Densely stacked concave lens arrays; (b) 3D images obtained by laser scanning confocal microscope (LSCM); (c) cantilever beam; (d) microvia cantilever beam; (e) microlens cantilever beam; (f) microvia array prepared on silicon wafer; concave microlens arrays (g) before and (h) after etching

Fig. 3. Fabrication of Fresnel lens inside sulfur-based glass^[36]. (a) Phase distributions at center wavelength of 550 nm; (b) microscope photograph of prepared Fresnel lens; (c) first-order microscope field diaphragm of Fresnel lens

Fig. 4. Three-dimensional fabrication of Fresnel lens on silicon surface^[37]. (a) Scanning electron microscope (SEM) image before etching for 6 min; (b) SEM image after etching for 6 min; (c) 3D morphology and (d) cross-section profile characterized by LSCM; demonstrations of (e) focusing and (f) imaging

Fig. 5. Laser-induced nanograting structure with reduced reflection^[39]. (a) SEM image of femtosecond laser-induced periodic surface structure on silicon; (b)‒(d) silicon sample exhibits various shades of dark colors at different viewing angles

Fig. 6. Diamond sub-wavelength anti-reflective structure^[40] . (a) SEM image of laser-induced formation of subwavelength structure on diamond surface; (b) detail at higher magnification; reflection and absorption spectra of diamond samples in wavelength range of 300‒2500 nm (c) before and (d) after femtosecond laser treatment

Fig. 7. Hypersurface structure^[42]. (a) Experimental setup of femtosecond laser interference; (b) SEM image of 20 μm×20 μm area composed of Si-based Mie resonator with scale of 1 μm

Fig. 8. Fabrication of microlens array on silicon surface by femtosecond laser composite processing technique^[43]. (a) SEM image of uniform microlens arrays; (b) 3D morphology analysis; (c) imaging device; (d) demonstration of microlens array imaging effect

Fig. 9. Sapphire transcribed K9 glass large field-of-view infrared artificial compound eye^[46]. (a) Production diagram of fabrication of sapphire concave compound eye template and K9 glass compound eye; (b) photo image of K9 glass compound eye with 5 mm scale bar; (c) SEM image with 100 μm scale bar; (d) amplified SEM image and local-amplified SEM image of K9 glass compound eye shown in inset with 100 µm and 20 µm scale bars, respectively; (e) 3D drawing of K9 glass compound eye; (f) cross-section profile of K9 glass compound eye; (g) diameter and height uniformity of ommatidia from center to edge of macrolens

Fig. 10. Femtosecond laser direct writing of phosphorus-doped black silicon^[47]. SEM images (titled 45°) of phosphorus-doped black silicon fabricated at laser fluences of (a) 0.28 J/cm², (b) 0.56 J/cm², (c) 0.84 J/cm², and (d) 1.12 J/cm²; (e) absorptance of crystalline silicon substrate and samples before (solid lines) and after annealing (dash dot lines); (f) Hall-effect measurement for sheet carrier concentration and mobility of phosphorus-doped silicon at different laser energy densities; (g) Hall-effect measurement for sheet carrier concentration and mobility of phosphorus-doped silicon at different annealing temperatures

Fig. 11. Infrared absorbing metasurface prepared by femtosecond laser direct writing technique^[49]. (a) Geometry and parameters of low-reflectance helix-based perfect absorption structure for IR spectral range; (b) simulated optical spectra of perfect absorption structure; (c) geometry and parameters of realistic perfect absorption structure obtained via femtosecond laser direct writing and metalization, with shape of single helix fabricated by femtosecond direct laser writing technique shown in inset; (d) absorbance spectra and simulated absorption spectra of single helix fabricated by femtosecond laser direct writing technique; (e) fabrication of dielectric template using laser direct writing lithography; (f) metalization of samples by gold sputtering using stage tilted at 45° angle; (g)(h) detailed views of metal helix; (i) experimental absorbance spectra of perfect absorption structure

Fig. 12. Sapphire mid-infrared bionic compound eye with increased permeability structure^[19]. (a) Photograph of moth compound eye; (b) LSCM image of moth eye; (c) SEM image of moth eye and high-resolution SEM image of microstructure on moth eye surface shown in inset; (d) schematic of fabrication process of anti-reflective sapphire surface with sub-wavelength microstructure; (e)‒(g) SEM images of sub-wavelength structures on sapphire; (h) experimentally measured transmittance of sapphire with smooth surface, single-sided antireflective structure, and double-sided antireflective structure; (i) transmittance versus angle of incidence for attenuated reflection structure at wavelength of 4 µm

Fig. 13. Fabrication of permeation-enhancing microstructures on magnesium fluoride surfaces by femtosecond laser processing technique ^[51]. (a) 3D image of LSCM for large-area manufactured truncated cone array; (b)‒(d) SEM images of large-area manufactured truncated cone array; statistical values of (e) widths and (f) heights of truncated cone arrays; (g) transmittance test results of treated MgF₂ and untreated MgF₂; (h) comparison of research results on anti-reflective surface microstructures; (i)(j) transmittance of treated MgF₂ at different incidence angles

Fig. 14. SEM images of permeation-enhancing microstructure and sub-wavelength antireflection microstructure prepared by femtosecond laser direct writing on zinc selenide surface^[52]. (a) Pyramid-square; (b) pyramid-hexagon; (c) cone-square; (d) cone-hexagon; (e) measured transmittance of fabricated sub-wavelength structure on ZnSe using Fourier transform infrared spectrometer

Fig. 15. Fabrication of high reflection fiber Bragg grating with indium fluoride glass core by femtosecond laser processing^[54]. (a) Schematic; (b) transmission spectra of grating before and after annealing at 150 ℃