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PhD student position

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Français - Anglais

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General information

Reference : UMR7588-BERBON-001
Workplace : PARIS 05
Date of publication : Monday, November 04, 2019
Scientific Responsible name : Bernard Bonello
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 6 January 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

When an ordered system such as a crystalline solid, a phononic, photonic or optomechanical crystal ... is structurally disturbed, the waves propagating there undergo multiple diffusions which, for important degrees of disorder, lead to the spatial confinement of the waves. . It is this phenomenon, known as Anderson's localization, that we want to demonstrate experimentally in two-dimensional random environments, the ultimate goal being to locate elastic waves and electromagnetic waves on the same sites. In addition to its interest in a better global understanding of the behavior of localized waves, this "metasurface" should ultimately enable the co-localization of photons and phonons on scattering clusters with lateral dimensions smaller than λ / 10, where λ is the common value of optical and acoustic wavelengths. Extreme confinement is expected to exalt the photon / phonon coupling with the perspective of applications for the coding of information: elastic modes located randomly on the metasurface can be seen as states 0 or 1 that can be read by the optical modes when they are located on the same sites.

The first step will be to determine which kind of disorder (of position and / or size) and which law of random distribution (binomial law, Poisson ...) is best able to lead to the localization. The objective is to find a relationship between the nature and the degree of disorder on the one hand and the elastic and / or optical field located on a cluster of scatters on the other hand. The numerical results will make it possible to prepare metasurfaces with a perfectly controlled degree and nature of disorder. The structures having to support the localization of electromagnetic waves at the telecom wavelength (1.5 microns), the typical dimensions of the diffusers are a few tens to a few hundred nanometers. Their development therefore requires the implementation of nano-fabrication techniques available the IEMN technology center in Lille. The experimental techniques used to highlight the phenomenon of localization are based on the use of ultra-fast lasers (picosecond and femtosecond) for the excitation of very high frequency (50 MHz - 2 GHz) elastic waves. The detection of localized waves will be done using interferometric techniques, combined with a very high spatial and temporal resolution, to follow both the path and the amplitude of the wave at any point on the surface of the samples.
Acoustic excitation will be from surface acoustic waves, while localized plasmon modes are created by illumination at the metal-insulator-metal interfaces (between the gold layer and the pillars). The effect of the disorder, and more particularly the different rules of mathematical probabilities on the particle distributions, will be studied with respect to nanometric localization, transport phenomena and optomechanical interactions in the phononic / photonic (phoXonic) structure. . Beyond the confinement within individual pillars and their interactions, we expect super locations in groups of N resonators that can in turn lead to physical properties such as Anderson-type localization. In addition, by increasing the density of the resonators, we expect to define a critical threshold beyond which the properties of the metamaterial change, as can be seen for example in the percolation limit. Finally, we will study the simultaneous localization of EM and acoustic fields in the nanostructure and we will calculate their OM coupling. This simultaneous localization will be at the base of the phoXonic platform for the control and exaltation of OM coupling between EM and elastic waves.
With this project, we propose an original approach by combining physical and mathematical models. We will use numerical methods, in the time and frequency domains, to calculate dispersion, transmission, reflection and absorption curves, field maps, and state densities. The distribution of resonators will be defined and analyzed from mathematical probability and statistical processes, such as Poisson or Gibbs processes. Theoretical analysis will be coupled with experimental work, mainly based on transient networks, picosecond acoustics and high resolution optical microscopy. One of the ambitious objectives of the project will be to design and produce an acousto-optical time-resolved microscope. This new experimental OM tool will simultaneously measure the response of the EM signal under acoustic excitation.
In addition to the academic spin-offs, the project targets short and long-term perspectives. The first is to propose an OM component operating at telecommunication frequencies that can lead to features such as sources and phonon memories, or allow the emission, propagation and manipulation of phonons by means of OM interactions. Secondly, with the demonstration of the elastic signature, EM and OM of a metasurface, the thesis opens the way to an information coding. Indeed, with an OM record of the metasurface, it becomes possible to read optically a mechanical distribution of resonators. Such a perspective bridges the gap between the field of metamaterials and the science of information.

Work Context

The candidate will spend 15 consecutive months at the Interdisciplinary Carnot de Bourgogne laboratory (ICB - Dijon) in order to develop the parts of the thesis dedicated to the localization of phoTons and to the study of opto-mechanical interactions. He will then be under the Benoît Cluzel's scientific supervision who will also be co-director of the thesis. It is estimated that this stay will start at T0 + 15 months. The last six months of the thesis will be done at the INSP.

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