a, Schematic plot of the evanescent wave (Eew) around two nanoholes with different sizes on a dielectric. For the larger nanohole with a diameter comparable to the wavelength, the evanescent fields at each edge of the nanohole are independent and decay rapidly from the boundary. For the smaller nanohole with a deep-subwavelength aperture, the strong interaction between the two boundaries constructively enhances the optical intensity inside the nanohole and confines the light on a deep-subwavelength scale. b, Simulations of the E-field strength distribution for a titanium oxide film with a nanohole shown by the central white-out region (the intensity of the light inside the nanohole is close to maximum but is not shown for a better visualization). c, Schematic of the direct nanowriting of O-FIB (left) and the image of the free-form patterning obtained by birefringence microscope (right, upper) and scanning electron microscope (right, lower).
by Zhen-Ze Li, Lei Wang, Hua Fan, Yan-Hao Yu, Qi-Dai Chen, Saulius Juodkazis and Hong-Bo Sun