arXiv subjects

Sonia Melle

Publications and source records attributed to Sonia Melle.

5 recordsLinked to original sources

arXiv2018

FRET distance dependence from upconverting nanoparticles to quantum dots

Förster resonant energy transfer (FRET) with upconverting nanoparticles (UCNPs) as donors and quantum dots (QDs) as acceptors has been regarded as a promising tool for biosensing applications. In this work, we use time-resolved fluorescence spectroscopy to analyze the UCNP-to-QD FRET and we focus on the most relevant parameter of the FRET phenomenon, UCNP-QD distance. This distance is controlled by a nanometric silica shell around the UCNP surface. We theoretically reproduce the experimental results applying FRET theory to the distribution of emitting erbium ions in the UCNP. This simple model allows us to estimate the contribution of every erbium ion to the final FRET response and to explore different strategies to improve FRET efficiency.

cond-mat.mes-hall↗

arXiv2014

Morphology of anisotropic chains in a magneto-rheological fluid during aggregation and disaggregation processes

We study the morphology of the chain-like aggregates formed when a external constant and uniaxial magnetic field is applied to a magneto-rheological (MR) fluid. In order to characterize the conformation of the aggregates, we study the evolution of various fractal dimensions during aggregation and disaggregation processes (i.e., when the applied field is switched on and off), using video-microscopy and image analysis. Experiments have been performed by varying the values of two external parameters: the magnetic field amplitude and particle concentration. We found that the box-counting dimension, related with how the aggregates occupy the surrounding space, depends on the ratio $R_1/R_0$. During the first stage of the disaggregation process, when the particles are moving by Brownian motion inside the aggregate, Family-Vicsek scaling function is verified.

cond-mat.mtrl-sci↗

arXiv2010

Competition between the Modulation Instability and Stimulated Brillouin Scattering in a Broadband Slow Light Device

We observe competition between the modulation instability (MI) and stimulated Brillouin scattering (SBS) in a 9.2-GHz broadband SBS slow light device, in which a standard 20-km-long single-mode LEAF fibre is used as the SBS medium. We find that MI is dominant and depletes most of the pump power when we use an intense pump beam at ~1.55 μm, where the LEAF fibre is anomalously dispersive. The dominance of the MI in the LEAF-fibre-based system suppresses the SBS gain, degrading the SBS slow light delay and limiting the SBS gain-bandwidth to 126 dB \cdot GHz. In a dispersion-shifted highly nonlinear fibre, the SBS slow light delay is improved due to the suppression of the MI, resulting in a gain-bandwidth product of 344 dB \cdot GHz, limited by our available pump power of 0.82 W.

physics.optics↗

arXiv2009

Phase-controlled slow and fast light in current-modulated semiconductor optical amplifiers

We present a theoretical study of the slow and fast light propagation in semiconductor optical amplifiers based on coherent population oscillations. By modulating the injection current to force the population oscillations we can modify the delay or advancement of light signals. Specifically, it is shown that the relative phase of the optical signal to the bias current modulations can be used as a knob for changing light propagation from delay to advancement. In addition, we analyze the effect of the modulation current for slow light in vertical cavity surface emission lasers (VCSELs) by taking into account the cavity effects. It is shown that the change of the depth of the modulation allows to tune the structural resonance, which in turn produces an enhancement of the delay.

physics.optics↗

arXiv2001

Polarizable particles aggregation under rotating magnetic fields using scattering dichroism

We used scattering dichroism to study the combined effects of viscous and magnetic forces on the dynamics of dipolar chains induced in magnetorheological suspensions under rotating magnetic fields. We found that the chains adjust their size to rotate synchronously with the field but with a constant phase lag. Two different behaviors for the dichroism (proportional to the total number of aggregated particles) and the phase lag are found below or above a critical frequency. We obtained a linear dependence of the critical frequency with the square of the magnetization and with the inverse of the viscosity. The Mason number (ratio of viscous to magnetic forces) governs the dynamics. Therefore there is a critical Mason number below which, the dichroism remains almost constant and above which, the rotation of the field prevents the particle aggregation process from taken place being this the mechanism responsible for the decrease of dichroism. Our experimental results have been corroborated with particle dynamics simulations showing good agreement.

cond-mat.mtrl-sci↗