Signal reconstruction from a scanning near-field optical microscopy,
lock-in non-linear filtering and tomography.
Signal reconstruction from a scanning near-field optical
microscopy, lock-in non-linear filtering and tomography.
University of Technology of Troyes
12 rue Marie Curie - BP 2060 - F-10010 Troyes cedex , France
We want to retrieve physical properties of the complex interaction pattern
between light, nanostructures and probe from experimental data obtained
with near-field optical microscopes.
This problem is known as the reconstruction of near-field signal.
Development of algorithms in order to reconstruct and recover the optical
signal near-field and use of linear and non-linear strategies in order to
explore the space of the solutions.
Results and prospects
Scanning Near-field Optical Microscopies suffer from the low signal to noise
ratio, due to the smallness of the diffracting probe used to get images.
Therefore a lock-in amplifier is commonly used to perform homodyne detection.
The detected signals are therefore the Fourier harmonics of the signal along
a vertical vibration of the probe and depend drastically on the vibration
All the the Fourier harmonics contain contribution of the ``near-field'' and
the ``far-field'' that are mixed in the near-field zone (i.e. at very short
Therefore, physical interpretation of contrast in high harmonics records
may be questionable.
From the lock-in data, we reconstruct the near-field intensity diffracted by
the probe-end in the case of approach curves.
Such a reconstructed optical signal can strongly differ from the detected
Thanks to the reconstruction which gives a tomography-like 3D map of the
detected signal, the vertical decay lengths can be measured directly,
from only one lateral scan.
Such a reconstruction of the optical signal in near-field zone permits to
study the influence of the lock-in amplifier and the probe vibration on
the measurement of the decay lengths of evanescent waves.
© Copyright 2007-2012 Thomas Grosges.