arXiv subjects

Aurélie Lecestre

Publications and source records attributed to Aurélie Lecestre.

6 recordsLinked to original sources

arXiv2019

Enhancement of electric and magnetic dipole transition of rare-earth doped thin films tailored by high-index dielectric nanostructures

We propose a simple experimental technique to separately map the emission from electric and magnetic dipole transitions close to single dielectric nanostructures, using a few nanometer thin film of rare-earth ion doped clusters. Rare-earth ions provide electric and magnetic dipole transitions of similar magnitude. By recording the photoluminescence from the deposited layer excited by a focused laser beam, we are able to simultaneously map the electric and magnetic emission enhancement on individual nanostructures. In spite of being a diffraction-limited far-field method with a spatial resolution of a few hundred nanometers, our approach appeals by its simplicity and high signal-to-noise ratio. We demonstrate our technique at the example of single silicon nanorods and dimers, in which we find a significant separation of electric and magnetic near-field contributions. Our method paves the way towards the efficient and rapid characterization of the electric and magnetic optical response of complex photonic nanostructures.

cond-mat.mes-hall↗

arXiv2018

Pushing the limits of optical information storage using deep learning

Diffraction drastically limits the bit density in optical data storage. To increase the storage density, alternative strategies involving supplementary recording dimensions and robust read-out schemes must be explored. Here, we propose to encode multiple bits of information in the geometry of subwavelength dielectric nanostructures. A crucial problem in high-density information storage concepts is the robustness of the information readout with respect to fabrication errors and experimental noise. Using a machine-learning based approach in which the scattering spectra are analyzed by an artificial neural network, we achieve quasi error free read-out of sequences of up to 9 bit, encoded in top-down fabricated silicon nanostructures. We demonstrate that probing few wavelengths instead of the entire spectrum is sufficient for robust information retrieval and that the readout can be further simplified, exploiting the RGB values from microscopy images. Our work paves the way towards high-density optical information storage using planar silicon nanostructures, compatible with mass-production ready CMOS technology.

physics.app-ph↗

arXiv2018

Fano-Resonances in High Index Dielectric Nanowires for Directional Scattering

High refractive index dielectric nanostructures provide original optical properties thanks to the occurrence of size- and shape-dependent optical resonance modes. These modes commonly present a spectral overlap of broad, low-order modes (\textit{e.g}. dipolar modes) and much narrower, higher-order modes. The latter are usually characterized by a rapidly varying frequency-dependent phase, which - in superposition with the lower order mode of approximately constant phase - leads to typical spectral features known as Fano resonances. Interestingly, such Fano resonances occur in dielectric nanostructures of the simplest shapes. In spheroidal nanoparticles, interference between broad magnetic dipole and narrower electric dipole modes can be observed. In high aspect-ratio structures like nanowires, either the electric or the magnetic dipolar mode (depending on the illumination conditions) interferes with higher order multipole contributions of the same nature (electric or magnetic). Using the analytical Mie theory, we analyze the occurrence of Fano resonances in high-index dielectric nanowires and discuss their consequences like unidirectional scattering. By means of numerical simulations, we furthermore study the impact on those Fano resonances of the shape of the nanowire cross-sections as well as the coupling of two parallel nanowires. The presented results show that all-dielectric nanostructures, even of simple shapes, provide a reliable low-loss alternative to plasmonic nanoantennas.

physics.app-ph↗

arXiv2017

Strongly directional scattering from dielectric nanowires

It has been experimentally demonstrated only recently that a simultaneous excitation of interfering electric and magnetic resonances can lead to uni-directional scattering of visible light in zero-dimensional dielectric nanoparticles. We show both theoretically and experimentally, that strongly anisotropic scattering also occurs in individual dielectric nanowires. The effect occurs even under either pure transverse electric or pure transverse magnetic polarized normal illumination. This allows for instance to toggle the scattering direction by a simple rotation of the incident polarization. Finally, we demonstrate that directional scattering is not limited to cylindrical cross-sections, but can be further tailored by varying the shape of the nanowires.

cond-mat.mes-hall↗

arXiv2017

Evolutionary Multi-Objective Optimisation of Colour Pixels based on Dielectric Nano-Antennas

The rational design of photonic nanostructures consists in anticipating their optical response from simple models or as variations of reference systems. This strategy is limited when different objectives are simultaneously targeted. Inspired from biology, evolutionary approaches drive the morphology of a nano-object towards an optimum through several cycles of selection, mutation and cross-over, mimicking the process of natural selection. However, their extension to scenarii with multiple objectives demands efficient computational schemes. We present a numerical technique to design photonic nanostructures with optical properties optimized along several arbitrary objectives. This combination of evolutionary multi-objective algorithms with frequency-domain electro-dynamical simulations is used to design silicon nanostructures resonant at user-defined, polarization-dependent wavelengths. The spectra of pixels fabricated by electron beam lithography following the optimized design show excellent agreement with the targeted objectives. The method is self-adaptive to arbitrary constraints, and therefore particularly interesting for the design of complex structures within technological limits.

cond-mat.mes-hall↗

arXiv2011

A single layer hydrogen silsesquioxane (HSQ) based lift-off process for germanium and platinum

Primarily used as etch mask, single layer hydrogen silsesquioxane has never been investigated for lift-off technique. In this article, we propose a new technique where a single layer of hydrogen silsesquioxane, a negative tone electron beam resist, is used to make lift-off of germanium and platinum. Removal of exposed hydrogen silsesquioxane is tested for various concentrations of hydrofluoric acid. Ultrasonic agitation is also used to reduce the formation of flakes due to accumulation of matter (evaporated metal in our case) along the sidewalls of the lift-off narrow slots. Results demonstrate potential in applying the hydrogen silsesquioxane as a negative tone lift-off resist to pattern nanometer scale features into germanium and platinum layers.

cond-mat.mtrl-sci↗