Central Idea
Near-field optical microscopy has already
proved to be a powerful tool for studying the optical response
of photonic structures and in particular two dimensional
photonic crystal nano-cavities. Near-field microscopy permits
not only to get information about the optical properties of
these structures but it also allows to locally modify their
optical behavior.
Tip induced
Tuning
The local introduction of a
sub-wavelength dielectric tip in the near-field of a two
dimensional photonic crystal cavity induces a reversibletuning of the cavity
resonancewithout necessarily introducing significant losses.
Since the strength of the tip induced tuning is proportional
to the electric field stored in the structure, by simply
mapping the induced spectral shift one can obtain a high
resolution map of the local density of electromagnetic states.
Non linear Temperature
tuning by Near-field probes
A larger tuning efficiency can be
obtained also by exploiting the local heating induced by
near-field laser excitation at different excitation powers.
The temperature gradient due to the optical absorption results
in an index of refraction gradient which modifies the
dielectric surroundings of the cavity shifting the
opticalmodes. 
Polarization
sensitive near-field microscopy
Moreover by combining the high spectral
and spatial resolution supplied by near-field microscopy with
the polarization information it is possible to access not only
to the intensity associated to the total electric field inside
these kind of structure but also to their in-plane components
with a no-diffraction limited resolution.
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