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.