Second-order nonlinear optical effects are electric-dipole-forbidden in centrosymmetric materials, but become allowed
through magnetic-dipole and electric-quadrupole effects. Furthermore, such higher multipole effects can play a role also
in the response of non-centrosymmetric materials, as demonstrated for second-harmonic generation (SHG) from chiral
thin films of organic molecules and from metal nanostructures. For nanostructured materials, higher multipole effects can
occur due to elementary light-matter interactions or due to field retardation across nanoparticles. For SHG from metal
nanostructures, the latter mechanism was operative and associated with nanoscale defects, which attract strong local
fields. The evidence of multipolar SHG emission was obtained from the different radiative properties of the various
multipolar sources. The goal of the present work is to perform a more comprehensive multipolar analysis of SHG from
arrays of L-shaped metal nanoparticles. In particular, we seek evidence of the presence of multipole interactions also at
the fundamental frequency by performing detailed polarization measurements of the SHG response and relying on the
different transformation properties of the various multipolar interactions for SHG emitted in the transmitted and reflected
directions and for the fundamental beam incident on the metal or substrate side of the sample.
This report shortly describes calculation method related to guiding properties of the microstructure fibres. For the
modelling of wave propagation in such fibres in linear and nonlinear regimes the finite-difference vectorial-beam-propagation
method (FD-VBMP) has been chosen. This method offers high accuracy and allows investigating
longitudinally varying structures or propagation of optical waves with amplitudes varying under the effect of nonlinearity
and loss. In order to take into account the effects related to the finite fibre dimensions the transparent boundary
conditions (TBC) was used. The Split-Step Local Error method is implemented for correct estimation of the influence of
nonlinearity on the wave propagation in microstructure fibres. On the basis of this method the complete algorithm for the
numerical simulation of the wave propagation in microstructure fibres under the effect of nonlinearity has been
developed. The method allows optimising the structure of photonic crystal fibres (PCF) for maximising or minimising
nonlinear effects. Investigation of the properties of a wavelength converter based on a microstructure fibre was carried
out using simulation results in the nonlinear case. Modification of the method for optimisation of connection between
microstructure fibres and conventional fibres is also considered.
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