Fabrication of micro- and nano-structures in thin metallic films by femtosecond laser ablation

We report maskless microfabrication of periodic structures in thin metallic films by femtosecond laser ablation. Two-dimensional (2D) triangular arrays of circular apertures with diameter of about 0.6 - 0.8 mu m and a lattice period of 1.0 and 2.0 mu m were fabricated by single-and multiple laser pulse ablation of 35 nm thick gold films sputtered on glass substrates. Optical transmission spectra of the fabricated samples exhibit transmission bands at infrared wavelengths. Theoretical modeling of the optical properties by Finite-Difference Time-Domain (FDTD) technique indicates that these bands are associated with localized and propagating surface plasmon (SP) modes. FDTD simulations also indicate substantial resonant enhancement of the near-field intensity at the metal's surface. Laser ablation of thin metallic films is therefore a promising route for fast prototyping of planar metallic micro-and nano-structures applicable as frequency-selective surfaces (FSS) and SP substrates.