Electromagnetic near-field from the interaction between a guided mode and surface nano-defects

The intensity of the electromagnetic near-field produced by the interaction between a transverse electric (or transverse magnetic) guided mode and a surface nano-defect on otherwise planar structure is studied theoretically. A perturbation solution, up to fourth-order in the surface defect profile, of the reduced Rayleigh equation is used to obtain the intensity. The numerical results are calculated using a single or double Gaussian wells. Rapid oscillations of the near field are found whose period is the inverse of two times the mode propagation constant. The amplitude of the oscillations are controlled either, by the separation of the wells or by the spatial spectrum profile. A Fourier transform technique is used to reconstruct the surface defect profile from the near-field intensity obtained at constant height.