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Digital heterodyne holography for plasmonic nanostructures
Sarah Suck, doctorante. Crédits : ESPCI ParisTech
In this thesis we study the scattering characteristics of plasmonic nanostructures by improving and adapting digital heterodyne holography, which is a powerful tool delivering a three-dimensional cartography of scattered light, and which has the advantage of allowing fast full-field imaging.
Spectroscopic measurements were carried out to record the scattering spectra of single nanoobjects and complement holographic measurements.
In order to get a deeper insight into the measured far-field scattering characteristics, we developed a numerical model based on the finite element method. This model allowed us to simulate the scattered fields of nanostructures both in the near- and far-field either in a reflection or transmission configuration for the illumination. The model yielded a good agreement with experimental results.
We studied numerous gold nanostructures prepared by electron beam lithography on glass substrates, ranging from simple, elementary nanoobjects to novel nanostructures. While the former allowed us to validate the technique, more sophisticated structures allowed us to observe that their scattering pattern is extremely sensitive to external and internal factors, such as the polarization and the wavelength of the incident light or the structure’s geometry and its resonance wavelength. We recognize so called ``hot spots’’ in the far-field, which are zones on the chain that scatter light more intensely than others.
In addition, we show that the technique of photothermal heterodyne holography is a novel method to study the temperature increase and heat distribution in heated plasmonic nanostructures due to its ability to directly probe a temperature increase.