Near-field diffraction by a magneto-optical grating in a ferromagnetic film

Theoretical analysis of the near-field magneto-optical (MO) diffraction of light propagating through a ferromagnetic. film by a domain structure has b een carried out. The results are expressed in terms of the classical theory of diffraction gratings, namely the effective perturbation of the index of refraction and generalised Bragg condition, extended to the near-field cas e. The near-field case is characterised by a wider variety of types of diff raction, which includes diffraction by in-plane polarisation, both anisotro pic and isotropic. It has been shown, analytically and numerically, that th e effective layer of a ferromagnetic film that actively contributes to the MO diffraction is severely limited by the Bragg condition, being of the ord er of d/4, where d is the period of the diffraction grating. Any further in crease in the thickness leads only to additional optical losses due to the light absorption. This can explain the lack of resolution reported in the n ear-field MO experiments where relatively thick garnet films were used. (C) 2001 Published by Elsevier Science B.V.