Optical FIB: Far-field fabrication with real-nanoscale spatial resolution in any solid materials

How to overcome the diffraction barrier of light in the far-field region to obtain subwavelength processing resolution has always been an important issue in advanced optical manufacturing. The traditional strategy to achieve this goal is to use the nonlinear threshold effect of materials, such as femetosecond laser induced two-photon polymerization (TPP) [1] . By introducing the stimulated radiation loss mechanism, the resolution of TPP can further reach tens of nanometers [2] . However, for solid materials, there is still no such a universal method that can realized robust and controllable nanoscale resolution for programable patterning. Here, we report an optical far-field-induced near-field breakdown technology [3] , which we abbreviate it as optical FIB, that in principle can be applied to any solid materials. The core idea of this technology is to invoke the initial optical damage created by ultrafast laser as a near-field probe (usually a nanohole, see Fig. 1 ), to trigger the subsequent subwavelength light confinement around the seed. Then, the far-field energy can be efficiently transferred to the near-field hotspot which is not restricted by the diffraction limit ( Fig. 1 ,left), thereby permitting a deep subwavelength direct writing resolution (18 nm, 1/40 λ for 800 nm pulse). The orientation of this near-field hotspot is always perpendicular to laser polarization due to the constraint of the electrical displacement continuity condition. By a simple polarization control of the incident light for steering nano-groove writing along the designed pattern, free-form nanowriting can be achieved while all the advantages of far-field optical direct writing can be maintained.