Holographic laser fabrication of 3D artificial compound μ-eyes

The demand for fast optical image acquisition without movable optical elements(e.g.,for self-driving car technology)can be met using bioinspired 3D compound eyes.3D laser processing strategies enable designable 3D structuring but suffer from low fabrication efficiency,which significantly limits their applications in producing complex 3D optical devices.Herein,we demonstrate a versatile yet simple wet-etching-assisted holographic laser fabrication method for the development of 3D compound eyes.Artificial compoundμ-eyes can be readily fabricated by programming a 3D spot array for the parallel ablation of a curved fused silica surface,followed by controllable etching in a hydrofluoric(HF)acid solution.A 3D-concave-lens array made on a curved surface over an area of 100μm cross-section with each lenslet of 10μm radius was fabricated with high fidelity and excellent imaging/focusing quality.The resultant 3D-concave-lens can serve as a hard template for the mass production of soft compound eyes through soft lithography.Additionally,using a generative adversarial network(GAN)-based deep learning algorithm,image restoration was conducted for each lenslet,which retained a large field of view and significantly improved image quality.This method provides a simple solution to the requirements of compoundμ-eyes required by Industry 4.0.

O-FIB:far-field-induced near-field breakdown for direct nanowriting in an atmospheric environment

Nanoscale surface texturing,drilling,cutting,and spatial sculpturing,which are essential for applications,including thin-film solar cells,photonic chips,antireflection,wettability,and friction drag reduction,require not only high accuracy in material processing,but also the capability of manufacturing in an atmospheric environment.Widely used focused ion beam(FIB)technology offers nanoscale precision,but is limited by the vacuum-working conditions;therefore,it is not applicable to industrial-scale samples such as ship hulls or biomaterials,e.g.,cells and tissues.Here,we report an optical far-field-induced near-field breakdown(O-FIB)approach as an optical version of the conventional FIB technique,which allows direct nanowriting in air.The writing is initiated from nanoholes created by femtosecondlaser-induced multiphoton absorption,and its cutting“knife edge”is sharpened by the far-field-regulated enhancement of the optical near field.A spatial resolution of less than 20 nm(λ/40,withλbeing the light wavelength)is readily achieved.O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern.The universality of near-field enhancement and localization makes O-FIB applicable to various materials,and enables a large-area printing mode that is superior to conventional FIB processing.

Ultralow-loss geometric phase and polarization shaping by ultrafast laser writing in silica glass

Polarization and geometric phase shaping via a space-variant anisotropy has attracted considerable interest for fabrication of flat optical elements and generation of vector beams with applications in various areas of science and technology.Among the methods for anisotropy patterning,imprinting of self-assembled nanograting structures in silica glass by femtosecond laser writing is promising for the fabrication of space-variant birefringent optics with high thermal and chemical durability and high optical damage threshold.However,a drawback is the optical loss due to the light scattering by nanograting structures,which has limited the application.Here,we report a new type of ultrafast laser-induced modification in silica glass,which consists of randomly distributed nanopores elongated in the direction perpendicular to the polarization,providing controllable birefringent structures with transmittance as high as 99% in the visible and near-infrared ranges and >90% in the UV range down to 330 nm.The observed anisotropic nanoporous silica structures are fundamentally different from the femtosecond laser-induced nanogratings and conventional nanoporous silica.A mechanism of nanocavitation via interstitial oxygen generation mediated by multiphoton and avanlanche defect ionization is proposed.We demonstrate ultralow-loss geometrical phase optical elements,including geometrical phase prism and lens,and a vector beam convertor in silica glass.

Laser interference fabrication of large-area functional periodic structure surface

Functional periodic structures have attracted significant interest due to their natural capabilities in regulating surface energy, surface effective refractive index, and diffraction. Several technologies are used for the fabrication of these functional structures. The laser interference technique in particular has received attention because of its simplicity, low cost, and high-efficiency fabrication of large-area, micro/nanometer-scale, and periodically patterned structures in air conditions. Here, we reviewed the work on laser interference fabrication of large-area functional periodic structures for antireflection, self-cleaning, and superhydrophobicity based on our past and current research. For the common cases, four-beam interference and multi-exposure of two-beam interference were emphasized for their setup, structure diversity, and various applications for antireflection, self-cleaning, and superhydrophobicity. The relations between multi-beam interference and multi-exposure of two-beam interference were compared theoretically and experimentally. Nanostructures as a template for growing nanocrystals were also shown to present future possible applications in surface chemical control. Perspectives on future directions and applications for laser interference were presented.