Transmission of an obliquely incident beam of light through small apertures in a metal film

Abstract

International audienceWe recently found that the intensity of the electric near field of a triangular aperture in a metal film is strongly localized at one edge of the aperture for incident light polarized perpendicular to this edge. Previous numerical calculations of the near field of a triangular aperture in a planar metal film, using the field susceptibility technique, yielded a nearly quantitative agreement with the experiments. Using this numerical technique, we have investigated the influence of an obliquely incident plane wave on the near field of small circular and triangular apertures. An interpretation of the numerical results leads to a deeper understanding of the way in which light transmission through the aperture is excited. The data suggest that after excitation of currents in the metal film by the incident light, a scattering of these currents by the aperture generates the near field of the aperture. We found that the excitation of small apertures (size < 100 nm) is due to a tangential magnetic field whereas the perpendicular electric field plays no role. The excitation of a small aperture can thus be described exclusively by a magnetic polarizability. We found that for thin metal films an interference of the scattered field with the field transmitted through the metal film changes the near field pattern

Magnetic Nature of Light Transmission through a 5-nm Gap

“…Figure 3 displays the magnetic field amplitudes at the gap entrances with varying incident angle for three different widths of 5 nm, 400 nm, and 4.6 μm. Magnetic field formed on the 5-nm gap keeps up with the Fresnel equations 22 (Fig. 3 , red circles and solid line) in agreement with the experimental results.…”

Light scattering of rectangular slot antennas: parallel magnetic vector vs perpendicular electric vector

“…Because the surface current on the flat surface is proportional to the total tangential magnetic field, the scattering amplitude is also proportional to the total tangential magnetic field on the flat surface. The total tangential magnetic field, a superposition of the tangential components of the incident and reflected magnetic fields, can be obtained using Fresnel coefficients 31 . Accordingly, the scattering intensity ratio is expressed as follows:…”

On the optimum form of an aperture for a confinement of the optically excited electric near field

“…Changing the symmetry of the aperture by introducing the triangular form leads to an enhancement of the intensity at one edge and a suppression of the intensity at the other edges as well as at the concave corner opposite to the edge. Bortchagovsky et al (2006) investigated by numerical calculations also other parameters influencing the symmetry of the configuration such as the direction of the incident beam exciting the aperture. Choosing an oblique angle of incidence indeed leads to an improvement of the confinement of the near field for a circular aperture in a 50‐nm‐thick film of aluminium to one side of its rim and in the case of the triangular aperture a further improvement of the confinement to one edge can be obtained for an appropriate choice of the angle of incidence.…”

“…We ask here the question for a possibility to further improve the confinement and to optimize the absolute value of this localized intensity by a modification of the form of the triangular aperture. We address this question by numerical calculations on the basis of the same numerical algorithm as used in previous calculations by Colas des Francs et al (2005) and by Bortchagovsky et al (2006).…”