arXiv subjects

Emmanuel Fort

Publications and source records attributed to Emmanuel Fort.

28 records · Page 2Linked to original sources

arXiv2015

Revisiting time reversal and holography with spacetime transformations

Wave control is usually performed by spatially engineering the properties of a medium. Because time and space play similar roles in wave propagation, manipulating time boundaries provides a complementary approach. Here, we experimentally demonstrate the relevance of this concept by introducing instantaneous time mirrors. We show with water waves that a sudden change of the effective gravity generates time-reversed waves that refocus at the source. We generalize this concept for all kinds of waves introducing a universal framework which explains the effect of any time disruption on wave propagation. We show that sudden changes of the medium properties generate instant wave sources that emerge instantaneously from the entire space at the time disruption. The time-reversed waves originate from these "Cauchy sources" which are the counterpart of Huygens virtual sources on a time boundary. It allows us to revisit the holographic method and introduce a new approach for wave control.

physics.optics↗

arXiv2014

Interaction of two walkers: Wave-mediated energy and force

A bouncing droplet, self-propelled by its interaction with the waves it generates, forms a classical wave-particle association called a "walker." Previous works have demonstrated that the dynamics of a single walker is driven by its global surface wave field that retains information on its past trajectory. Here, we investigate the energy stored in this wave field for two coupled walkers and how it conveys an interaction between them. For this purpose, we characterize experimentally the "promenade modes" where two walkers are bound, and propagate together. Their possible binding distances take discrete values, and the velocity of the pair depends on their mutual binding. The mean parallel motion can be either rectilinear or oscillating. The experimental results are recovered analytically with a simple theoretical framework. A relation between the kinetic energy of the droplets and the total energy of the standing waves is established.

physics.class-ph↗

arXiv2014

Self-organization into quantized eigenstates of a classical wave driven particle

A growing number of dynamical situations involve the coupling of particles or singularities with physical waves. In principle these situations are very far from the wave-particle duality at quantum scale where the wave is probabilistic by nature. Yet some dual characteristics were observed in a system where a macroscopic droplet is guided by a pilot-wave it generates. Here we investigate the behaviour of these entities when confined in a two-dimensional harmonic potential well. A discrete set of stable orbits is observed, in the shape of successive generalized Cassinian-like curves (circles, ovals, lemniscates, trefoils...). Along these specific trajectories, the droplet motion is characterized by a double quantization of the orbit spatial extent and of the angular momentum. We show that these trajectories are intertwined with the dynamical build-up of central wave-field modes. These dual self-organized modes form a basis of eigenstates on which more complex motions are naturally decomposed.

quant-ph↗

arXiv2013

Confocal supercritical angle fluorescence microscopy for cell membrane imaging

We demonstrate sub-wavelength sectioning on biological samples with a conventional confocal microscope. This optical sectioning is achieved by the phenomenon of supercritical angle fuorescence, wherein only a fluorophore next to the interface of a refractive index discontinuity can emit propagating components of radiation into the so-called forbidden angles. The simplicity of this technique allows it to be integrated with a high numerical aperture confocal scanning microscope by only a simple modification on the detection channel. Confocal-SAF microscopy would be a powerful tool to achieve high resolution surface imaging, especially for membrane imaging in biological samples

physics.optics↗

arXiv2013

Nanoroughened plasmonic films for enhanced biosensing detection

Although fluorescence is the prevailing labeling technique in biosensing applications, sensitivity improvement is still a striving challenge. We show that coating standard microscope slides with nanoroughened silver films provides a high fluorescence signal enhancement due to plasmonic interactions. As a proof of concept, we applied these films with tailored plasmonic properties to DNA microarrays. Using common optical scanning devices, we achieved signal amplifications by more than 40-fold.

physics.ins-det↗

arXiv2013

Path-memory induced quantization of classical orbits

A droplet bouncing on a liquid bath can self-propel due to its interaction with the waves it generates. The resulting "walker" is a dynamical association where, at a macroscopic scale, a particle (the droplet) is driven by a pilot-wave field. A specificity of this system is that the wave field itself results from the superposition of the waves generated at the points of space recently visited by the particle. It thus contains a memory of the past trajectory of the particle. Here, we investigate the response of this object to forces orthogonal to its motion. We find that the resulting closed orbits present a spontaneous quantization. This is observed only when the memory of the system is long enough for the particle to interact with the wave sources distributed along the whole orbit. An additional force then limits the possible orbits to a discrete set. The wave-sustained path memory is thus demonstrated to generate a quantization of angular momentum. Because a quantum-like uncertainty was also observed recently in these systems, the nonlocality generated by path memory opens new perspectives.

cond-mat.soft↗

arXiv2013

Trajectory eigenmodes of an orbiting wave source

Resonances usually result from wave superpositions in cavities where they are due to the wave spatio-temporal folding imposed by the boundaries. These energy accumulations are the signature of the cavity eigenmodes. Here we study a situation in which wave superposition results from the motion of a source emitting sustained overlapping waves. It is found that resonances can be produced in an unbounded space, the boundary conditions being now defined by the trajectory. When periodic trajectories are investigated, it is found that for a discrete subset of orbits, resonant wave modes are excited. Trajectory eigenmodes thus emerge. These modes have three attributes. Their associated resonant wave fields are the Fourier transform of the source's trajectory. They are non-radiative and they satisfy the perimeter Bohr-Sommerfeld quantization rule.

physics.class-ph↗

arXiv2013

Full Field Supercritical Angle Fluorescence Microscopy for live cell imaging

We introduce a full field fluorescence imaging technique with axial confinement of about 100 nm at the sample/substrate interface. Contrary to standard surface imaging techniques, this confinement is obtained through emission filtering. This technique is based on supercritical emission selectivity. It can be implemented on any epifluorescence microscope with a commercial high numerical aperture objective and offers a real time surface imaging capability. This technique is of particular interest for live cell membrane and adhesion studies. Using HEK cells, we show that one can observe simultaneously the surface and in-depth cell phenomena.

physics.optics↗

arXiv2013

Gold nanocrescents for remotely measuring and controlling local temperature

We present a novel technique to remotely measure and control the local temperature within a medium. This technique is based on the observation of the rotational Brownian motion of gold nanocrescent particles, which possess a strong anisotropic light interaction due to their plasmonic properties. Rotational scattering correlation spectroscopy performed on a single nanoparticle is able to determine the local temperature with high accuracy. These nano-thermometers can simultaneously play the role of nano-heaters when absorbing the light of a focused laser beam.

cond-mat.mes-hall↗

arXiv2013

Mutual adaptation of a Faraday instability pattern with its flexible boundaries in floating fluid drops

Hydrodynamic instabilities are usually investigated in confined geometries where the resulting spatiotemporal pattern is constrained by the boundary conditions. Here we study the Faraday instability in domains with flexible boundaries. This is implemented by triggering this instability in floating fluid drops. An interaction of Faraday waves with the shape of the drop is observed, the radiation pressure of the waves exerting a force on the surface tension held boundaries. Two regimes are observed. In the first one there is a coadaptation of the wave pattern with the shape of the domain so that a steady configuration is reached. In the second one the radiation pressure dominates and no steady regime is reached. The drop stretches and ultimately breaks into smaller domains that have a complex dynamics including spontaneous propagation.

physics.flu-dyn↗