02 October 2014 Congratulations to New ICFO PhD graduate

Thesis Committee

Dr. Ana Asenjo graduated from Universidad Complutense de Madrid with a thesis in ‘Plasmon, light, and electron beam interactions at the nanoscale’ Dr. Ana Asenjo received her Master Degree in Fundamental Physics from the Universidad Complutense de Madrid before joining the Nanophotonics theory research group at ICFO, led by ICREA Professor at ICFO Javier García de Abajo. She centered her doctoral work on the plasmonic and chiral response of nanostructures, and on the interactions of these nanostructures with light and electron beams. Dr. Asenjo’s thesis, entitled ‘Plasmon, light, and electron beam interactions at the nanoscale’ was supervised by Dr. Javier García de Abajo.

Abstract:

Among the many materials that have been considered for controlling and engineering light fields at the nanoscale, metals play a major role. The collective oscillations of their conduction electrons, the so-called plasmonic excitations, are of paramount importance in the field of nanophotonics. Essentially, metallic particles confine light to tiny spaces and produce intense field enhancement. Besides its fundamental interest, plasmonics has strikingly diverse implications in technology. The interaction between light, matter, and electron beams gives rise to many fascinating phenomena, some of them still not well understood. In this context, the aim of this thesis is twofold: first, to provide theoretical insight about some fundamental issues; second, to propose or confirm experimental work that might lead to technological applications.

Firstly, we have built a theoretical framework that explains how the rotation of a spinning metallic nanoparticle affects its optical response. Due to the rotation, the body scatters light inelastically, constituting an example of rotational Doppler shift. Moreover, when the frequency of rotation is higher than that of the incoming light, the system becomes superradiant and generates stimulated emission. We have also studied the experimental feasibility of such system: under proper light illumination, the particle acquires remarkable spinning velocities without melting, which opens the door to future experimental realizations.

In addition we have also studied the interaction of plasmonic chiral matter with both circularly polarized light and vortex electron beams. For light, we have compared calculations based upon multiple scattering theory with recent observations of circular dichroism in plasmonic nanoparticles assembled using DNA origami. For electrons, we have predicted strong dichroism in the electron energy-loss spectroscopy (EELS) signal by using vortex beams. These electrons carry orbital angular momentum that can be exchanged in the interaction with chiral plasmons. We have also shown that electron vortex beams display a dichroic response when probing chiral biomolecules, which suggests the use of these vortex for resolving different enantiomers.

Finally we have focused our research on the phenomenon of plasmon-mediated electron energy gain, in which the interaction of swift electrons with strong evanescent light fields scattered by a nanostructure (e.g., by excitation of a plasmon by an external laser beam) can produce energy gains in the electrons and stimulated photon emission. This electron-light interaction can provide detailed information on the optical properties of the sampled nanostructures in the time and frequency domains. The so-called electron energy-gain spectroscopy should provide an unprecedented combination of energy and space resolution, combined with temporal control provided by the light pulse.


Thesis Committee:

Prof. Rosario Martínez – Universidad Complutense de Madrid
Prof. Fernando Sols – Universidad Complutense de Madrid
Prof. Laura Na Liu – Max Planck Institute for Intelligent Systems
Prof. Luis M. Liz-Marzán – CIC Biomagune
Prof. Guillermo Gómez – Universidad Autónoma de Madrid

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