Experimental observation of the scattering of light by planar metallic nanoparticles -: art. no. 160

It is known that the efficiency of scattering of light by a particle is related to its size, geometry and optical constants of the material, since the theory of scattering by small particles developed by Mie in the beginning of the 20th century. However, the Mie scattering theory is valid just for a few special cases like a homogeneous sphere embedded on a medium of homogenous refraction index. More recently, some theoretical simulations on planar nanoparticles have shown that the optical resonances are dependent on the shape of the particle. Simultaneously, local field enhancements take place on the particles when excited by an incident wave. A comprehensive knowledge of the optical behaviour of planar particles is of great importance for the development of optical devices at the nanoscale, as well as for the fast developing field of photonic crystals and the emerging field of diffractive optics. In this paper, we present optical investigations on arrays of triangular nanoparticles with sizes comparable with the wavelength. Particles were produced using the method developed by Fischer and the optical measurements have been made using a scanning confocal microscope and a total-internal-reflection system. The scattering of light by particles of some materials when excited by an evanescent field show a strong dependence on their relative orientation in the direction of incidence. The measured scattering patterns change with the polarization of light.