arXiv subjects

Aymeric Braud

Publications and source records attributed to Aymeric Braud.

5 recordsLinked to original sources

arXiv2026

Wave drag in moving plasmas: recent developments and prospects

Wave propagation in a medium differs depending on whether this medium is at rest or moving with respect to an observer. Motion can notably lead to modifications of the wave trajectory, of its polarization, or of its transverse structure. Although these effects are well documented in isotropic dielectrics, they remain largely unexplored and unaccounted for in plasmas, despite the fact that simple models suggest they could in fact be large under certain conditions, as well as recent experimental observations. Here we first review existing models for motion effects on plasma waves, then identify a number of basic challenges that lie in the way of using these models to quantify motion effects in realistic configurations, and finally discuss possible workarounds.

physics.plasm-ph↗

arXiv2026

Spin-redirection Berry phase with planar rays

Geometric or Berry phases are fundamental manifestations that appear in many areas of physics. They arise from the geometry of the space describing the properties of multi-component wave fields. An important example for electromagnetic waves is the spin-redirection Berry phase associated with the evolution of the spin direction. Because this effect has traditionally been studied in isotropic media where the spin is aligned with the ray trajectory, it has become commonly assumed that this spin-redirection Berry phase requires nonplanar rays. Here we show that a spin-redirection phase can in fact arise along a planar ray if the spin evolves along the ray. We expose this effect through the singular example of a moving unmagnetized plasma, and demonstrate how this behavior can more generally arise from a finite transverse spin. In identifying this new spin-redirection mechanism our work not only provides the tools to discover additional manifestations of SOIs in nature, but also uncovers supplemental degrees of freedom to harness SOIs to control light.

physics.optics↗

arXiv2025

Spin-orbit interactions induced by light drag in moving media

Spin-orbit interactions (SOIs) of light are manifestations of coupling between components of light's angular momentum. They are at play in most basic optical processes, offering opportunities both to understand their fundamental origin and to control light in novel ways. Because SOIs become significant at subwavelength scale, they have largely been explored in the context of inhomogeneous materials exhibiting wavelength-scale structures, and notably metamaterials. Here we demonstrate that spin-orbit interactions can in fact analogously emerge in moving matter through the well-known light-dragging effects. SOIs in moving media are shown to manifest through a Berry phase induced by vorticity, which then leads to a rotation of the wave's polarization. In bringing together electrodynamics of moving media and SOIs of light, our work not only paves the way for the discovery of new fundamental effects but also uncovers novel means to harness SOIs to control light.

physics.optics↗

arXiv2024

Ray tracing methods for wave propagation in moving anisotropic media : application to magnetized plasmas

The propagation of a wave in a medium is generally affected when the medium is moving with respect to the observer. Because plasma equilibria often involve plasma flows, for instance in astrophysics or in magnetic confinement nuclear fusion devices, understanding the effect of motion on plasma waves is important. Meanwhile, the presence of a background magnetic field in a plasma makes it anisotropic. To address this problem, we derive here ray tracing equations for the trajectory of rays propagating in a moving anisotropic medium. The proposed approach is to use an effective dispersion relation for the moving medium as seen from the laboratory, obtained by performing a Lorentz transformation of the dispersion relation known for the medium at rest. This formalism is illustrated by considering the standard ordinary and extraordinary modes in a magnetized plasma at rest. Although we work here at lowest order in the geometrical optics approximation, this method is a first step towards higher order expansions, as required for instance to capture polarization effects.

physics.plasm-ph↗

arXiv2024

Fresnel drag in a moving magnetized plasma

The change in direction of the wavevector and group velocity experienced by a wave refracted at the interface of an anisotropic medium in uniform linear motion are determined analytically. These transmission conditions, which are shown to be consistent with generalized Snell's law written in the laboratory frame, are then used to examine the effect of motion on waves incident on a magnetized plasma. For an incident wave in the plane perpendicular to the magnetic field the motion is observed to lead to non negligible deviation of the low-frequency X-mode, as well as to non-symmetrical total reflection angles. These effects are shown to be further complicated when the magnetic field is in the plane formed by the incident wavevector and the medium's velocity, as the anisotropy now competes with the motion-induced drag. Although obtained in simplified configurations, these results suggest that accounting for motion when modeling plasma waves trajectory could be important under certain conditions, calling for a more detailed quantification of the effect of motion in actual diagnostics and plasma control schemes.

physics.plasm-ph↗