4 internationally renowned researchers gave lectures during the SSE#9

From January 9, 2023 to January 13, 2023

Aurélien CRUT, Florence TUPIN, Olivier MARTIN and Alessandro RIZZI gave courses during our 9th SLEIGHT Science Event

Aurélien CRUT from the Institut Lumière Matière (UCBL, CNRS) gave a lecture on "Vibrational and cooling dynamics of metal nanoparticles: experimental investigations and modeling".

The sudden absorption of energy by a metal nano-object launches a series of relaxation processes (internal thermalization, acoustic vibrations, cooling,…) involving femtosecond to nanosecond timescales, whose investigation allows to better understand how the macroscopic laws ruling electron interactions, elasticity, heat conduction or interfacial energy transfer are modified at the nanoscale. Optical pump-probe spectroscopy (based on the excitation of nano-objects by a femtosecond pump pulse, and the monitoring of their subsequent relaxation dynamics using another, time-delayed, probe pulse) constitutes a powerful experimental approach for such investigations. Moreover, the realization of such experiments on individual nano-objects and their analysis with multiphysics numerical simulations enable highly quantitative investigations of the ultrafast dynamics of metal nano-objects and of the transient changes of optical response that they induce.

Recent investigations on the vibrational and cooling dynamics of metal nano-objects were presented in this talk. These studies have in particular clarified the applicability of continuum mechanical models using bulk elastic constants to nanoparticles, and shown a promising approach to significantly improve the vibrational quality factors of supported nano-objects. They have also shed light on the dependence of the cooling dynamics of substrate-supported nano-objects on the morphological and thermal properties of the nano-objects and of their environment, and demonstrated that the sensitivity of time-resolved signals to transient heating largely depends on the probing wavelength.


Florence TUPIN, researcher at the Laboratoire Traitement et Communication de l'Information (LTCI) at Telecom Paris, presented her work on "SAR (Synthetic Aperture Radar) imaging: principle, applications, and a focus on deep learning approaches for speckle reduction"

SAR (Synthetic Aperture Radar) images are invaluable data for earth observation. They are obtained by emitting electro-magnetic waves with GHz frequencies, which are then backscattered by the earth surface and recorded by the antenna on a plane or a satellite. These images can be acquired at any time, regardless of the meteorological conditions, and provide information on the characteristics of the earth, its height, and its possible movement thanks to the phase information of the backscattered electro-magnetic field. A new generation of SAR sensors from state or private companies is currently imaging the earth with unprecedented spatial and temporal resolutions. Due to the coherent imaging of the SAR sensors, images present strong fluctuations due to the speckle phenomenon. This phenomenon is a major obstacle for the analysis and understanding of SAR images.

In her talk, she first introduced the principles of SAR imaging and presented some of the successful applications for cartography, height retrieval and ground movement monitoring. Advantages and drawbacks compared to optical systems were discussed. In the second part of he talk, she focus edon SAR data statistics and speckle reduction. She gave an overview of despeckling methods from those based on signal modeling through variational models or patches, to more recent ones based on deep learning with supervised and self-supervised strategies.

Olivier MARTIN, from the Nanophotonics & Metrology Laboratory at EPFL, gave a lecture on the fabrication and applications of plasmonic nanostructures.

Plasmonics studies the optical response of metallic nanostructures made from coinage metals (Au, Ag, Al, and a few others) which have an especially strong interaction with light in the visible part of the spectrum. For a given metal this interaction is also governed by the shape of the nanostructures and it is important to control their fabrication with un accuracy in the order of 20 nm. Nanotechnology is therefore at the heart of this field of research and, after a brief introduction to plasmonics, he described different approaches for the fabrication of plasmonic nanostructures. They can be divided into either top-down techniques like electron-beam lithography with lift-off or etching; or bottom-up approaches, such as chemical synthesis. For the latter, he showed that even human cells can produce plasmonic nanostructures by reducing a gold salt. Among the numerous applications of plasmonic nanostructures, he focused on near-field enhancement with its application to surface enhanced Raman spectroscopy and on the generation of strong optical forces with plasmonic nanostructures.

Besides, a collection of plasmonic nanostructures deposited on a surface can build a so-called metasurface – the modern equivalent of planar optics – with applications in holography and biosensing. Numerical simulations are also essential to guide these experiments at the nanoscale and the presentation will include some of our research efforts on the development of suitable numerical techniques that can match well the effectively fabricated nanostructures. Finally, he reported some on-going work on the design of plasmonic nano-motors using a machine learning approach and illustrate its suitability to discover plasmonic nanostructures with an especially strong torque under linear-polarized light illumination.
Olivier Martin, Nanophotonics and Metrology Lab at EPFL, during the SSE9
Olivier Martin, Nanophotonics and Metrology Lab at EPFL, during the SSE9

Alessandro RIZZI, from the Department of Computer Science at the University of Milan, described how vision is spatial and why we cannot measure color or spectrum if our device has a lens
Color is often considered as something that derives from the physical signal at the point. In reality it is generated by our vision system as response of something more complex. For practical and historical reasons colorimetry has been always based on strong simplifications and these simplifications have contributed to deeply fix the pointwise approach to color, and also our way to think about it. This talk presenedt some (probably unexpected) optical characteristics of our eye. Since it is a pretty poor camera, our vision has developed smart way to acquire visual information. Analyzing the generation of color sensation starting from our vision system, explain why our vision is spatial and ends in a series of important issues claimed in the title. We cannot measure color or spectrum if our device has a lens.
Alessandro RIZZI, from the University of Milano, during the SSE9
Alessandro RIZZI, from the University of Milano, during the SSE9