Evènements

Octobre 2017

Mardi, 3 Octobre, 2017

Séminaire

14h - Site Valrose

Drop impact and dynamic wetting with complex fluids

The impact of a liquid drop on a solid surface is a fascinating phenomenon we frequently observe in everyday life. Despite its apparent simplicity, drop impact conceals some nontrivial and challenging physics. The interest in understanding drop impact phenomena is also practical, because they play a major role in the optimization of several applications, such as additive manufacturing and spray applications, which are ubiquitous in industrial as well as in domestic processes, from painting or cleaning surfaces to injecting fuel into internal combustion engines. This seminar reviews some recent (and some not-so-recent) results about the impact and dynamic wetting of complex fluids drops on homo-thermal and heated surfaces, with focus on viscoelastic fluids (dilute polymer solutions) and viscoplastic (or yield-stress) fluids.

Mercredi, 4 Octobre, 2017

Séminaire

14h - Site Sophia

Effects of Nonlinearity and Disorder in Topological Photonics

In the first part of the talk, I discuss how optical nonlinearity alters the behavior of photonic topological insulators. In the nonlinear regime, band structures and their associated topological invariants cannot be calculated. Nonetheless, nonlinear photonic lattices can support moving edge solitons that "inherit" many properties of linear topological edge states : they are strongly self-localized, and propagate unidirectionally along the lattice edge. These solitons can be realized in a variety of model systems, including (i) an abstract nonlinear Haldane model, (ii) a Floquet lattice of coupled helical waveguides, and (iii) a lattice of coupled-ring waveguides.

Topological solitons can be "self-induced", meaning that they locally drive the lattice from a topologically trivial to nontrivial phase, similar to how an ordinary soliton locally induces its own confining potential. This behavior can be used to design nonlinear photonic structures with power thresholds and discontinuities in their transmittance ; such structures, in turn, may provide a novel route to devising nonlinear optical isolators.

In the second part of the talk, I discuss amorphous analogues of a two-dimensional photonic Chern insulator. These lattices consist of gyromagnetic rods that break time-reversal symmetry, arranged using a close-packing algorithm in which the level of short-range order can be freely adjusted. Simulation results reveal strongly-enhanced nonreciprocal edge transmission, consistent with the behavior of topological edge states. Interestingly, this phenomenon persists even into the regime where the disorder is sufficiently strong that there is no discernable spectral gap.

 

Mardi, 10 Octobre, 2017

Séminaire

14h - Site Valrose

Deformation processes in rocks and other polymineralic materials

Vendredi, 13 Octobre, 2017

11h- Site Valrose

The vacuum-birefringence search at BMV

In physics, vacuum has historically been defined as a region of space where light travels at the well-known calculated constant, c. In the early 20th century, the quantization of electromagnetism led to the development of the now well-tested theoretical framework of quantum electrodynamics (QED). An interesting, yet untested, prediction of QED is the non-constant, even anisotropic, propagation of light through vacuum. The origin of this anisotropy is that, in contrast to classical vacuum, QED vacuum can be polarized in the presence of an external electromagnetic field resulting in a birefringent vacuum, ∆nvac. The leading experiments in the field, PVLAS (Polarizzazione del Vuoto con LASer ; Ferrara, Italy) [1] and BMV (Biréfringence Magnétique du Vide ; Toulouse, France) [2], seek to measure this effect experimentally by observing the ellipticity induced in a linearly polarized laser field propagating through a region of birefringent vacuum. The BMV experiment, housed at the Laboratoire National des Champs Magnétique Intenses (LNCMI) in Toulouse, France, utilizes high-amplitude (B ≈ 20 T) pulsed magnetic fields in its efforts to measure vacuum polarization. The main challenge of the experiment lies in reaching the sensitivity required to measure the minute birefringence, ∆nvac = kvacB2, resulting from the small magnetic-birefringence constant of vacuum (kvac ≈ 4 × 10−24 T−2) predicted by QED ; a number which, as a result of the recent advancements in state-of-the-art precision interferometry owing largely to the successes of interferometric gravitational-wave detectors, is increasingly viable. The BMV collaboration seeks to accomplish this goal on two fronts : first, through collaboration with the LNCMI facility in the implementation of novel magnet technologies for signal production ; and second, through the development and characterization of an ultra-precise polarimeter for signal detection. Here we present the status of the BMV experiment with a focus on the optical apparatus.

[1] F. Della Valle et al., Phys. Rev. D 90, 092003 (2014).
[2] A. Cadène et al., Eur. Phys. J. D 68, 16 (2014).

 

Mardi, 17 Octobre, 2017

Soutenance

11h - Site Valrose

TBA