Extension of Bethe's diffraction model to conical geometry: Application to near-field optics
de Spectrométrie Physique, CNRS UMR5588, Université Joseph Fourier Grenoble -
BP 87, 38402 Saint Martin d'Hères cedex, France
Accepted: 2 April 2001
The generality of the Bethe's two-dipole model for light diffraction through a subwavelength aperture in a conducting plane is studied in the radiation zone for coated conical fiber tips as those used in near-field scanning optical microscopy. In order to describe the angular radiated power of the tip theoretically, we present a simple, analytical model for small apertures (radius ≲ 40 nm) based on a multipole expansion. Our model is able to reproduce the available experimental results. It proves relatively insensitive to cone angle and aperture radius and contains, as a first approximation, the empirical two-dipole model proposed earlier.
PACS: 42.25.Fx – Diffraction and scattering / 41.20.Jb – Electromagnetic wave propagation; radiowave propagation / 07.79.Fc – Near-field scanning optical microscopes
© EDP Sciences, 2001