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The extraordinary optical transmission through periodic
arrays of subwavelength holes has been studied
extensively since it was first reported in 1998, owing to
both its fundamental implications and its technological
potential. The picture of the underlying mechanism that
emerges from most of the theoretical studies is a resonant
process assisted by surface electromagnetic modes, such
as surface plasmons. However, these studies consider
an infinite array of holes. By combining experiment and
theory, we have analysed the influence of the inherent
finite size of the arrays and report here the unexpected
spatial distribution of light as it emerges from the arrays.
This distribution is strongly anisotropic and extremely
sensitive to the angle of incidence of the impinging light.
The behaviour can be explained by a model that takes
into account the asymmetry induced by the array edges,
and the effects this has on the emission pattern across
the array.
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