arXiv subjects

Yann Louyer

Publications and source records attributed to Yann Louyer.

5 recordsLinked to original sources

arXiv2025

Wavefront Shaping of Scattering Forces Enhances Optical Trapping of Levitated Nanoparticles

Optically-levitated nanoparticles in vacuum offer a pristine platform for high-quality mechanical oscillators, enabling a wide range of precision measurements and quantum technologies. A key performance metric in such systems is the stiffness of the optical trap, which is typically enhanced by increasing laser power-at the cost of unwanted heating, reduced coherence, and enhanced quantum backaction. Here, we demonstrate a fundamentally new route to increasing trap stiffness: wavefront shaping of the optical field. By tailoring the spatial phase profile of the trapping beam, we significantly boost the mechanical confinement of subwavelength particles without raising the optical intensity. Remarkably, this enhancement arises from a selective reduction of non-conservative optical forces, while preserving the conservative restoring forces that define trap stiffness. As a result, mechanical nonlinearities are also reduced, improving stability at low pressures. Our findings challenge the long-standing assumption that diffraction-limited focusing is optimal for dipolar Rayleigh particles, and establish wavefront shaping as a powerful, readily applicable tool to control optomechanical forces in levitation experiments. This opens new avenues for minimizing backaction, reducing thermal decoherence, and expanding the range of materials that can be stably levitated.

physics.optics↗

arXiv2022

Non-Gaussian diffusion near surfaces

We study the diffusion of particles confined close to a single wall and in double-wall planar channel geometries where the local diffusivities depend on the distance to the boundaries. Displacement parallel to the walls is Brownian as characterized by its variance, but it is non-Gaussian having a non-zero fourth cumulant. Establishing a link with Taylor dispersion, we calculate the fourth cumulant and the tails of the displacement distribution for general diffusivity tensors along with potentials generated by either the walls or externally, for instance gravity. Experimental and numerical studies of the motion of a colloid in the direction parallel to the wall give measured fourth cumulants which are correctly predicted by our theory. Interestingly, contrary to models of Brownian-yet-non-Gaussian diffusion, the tails of the displacement distribution are shown to be Gaussian rather than exponential. All together, our results provide additional tests and constraints for the inference of force maps and local transport properties near surfaces.

cond-mat.soft↗

arXiv2021

Stochastic Inference of Surface-Induced Effects using Brownian Motion

Brownian motion in confinement and at interfaces is a canonical situation, encountered from fundamental biophysics to nanoscale engineering. Using the Lorenz-Mie framework, we optically record the thermally-induced tridimensional trajectories of individual microparticles, within salty aqueous solutions, in the vicinity of a rigid wall, and in the presence of surface charges. We construct the time-dependent position and displacement probability density functions, and study the non-Gaussian character of the latter which is a direct signature of the hindered mobility near the wall. Based on these distributions, we implement a novel, robust and self-calibrated multifitting method, allowing for the thermal-noise-limited inference of diffusion coefficients spatially-resolved at the nanoscale, equilibrium potentials, and forces at the femtoNewton resolution.

cond-mat.soft↗

arXiv2019

Nonequilibrium dynamics induced by scattering forces for optically trapped nanoparticles in strongly inertial regimes

As a first approximation, the forces acting on optically trapped particles are commonly assumed to be conservative. The influence of the nonconservative force has been shown to be negligible in overdamped liquid environments. However, its impact in the underdamped regime remains unexplored. Here, we experimentally study the combined effects of gradient and scattering forces on the nonlinear dynamics of trapped particles at various air pressures, leading to significant low-frequency noise excess along the optical axis and the emergence of toroidal Brownian vortices. Our results supported, by numerical simulations and a theoretical model, provide fundamental insights into the functioning of optical tweezers and a means for investigating nonequilibrium steady states in the presence of nonconservative forces.

physics.optics↗

arXiv2018

The role of non-conservative scattering forces and damping on Brownian particles in optical traps

We consider a model of a particle trapped in a harmonic optical trap but with the addition of a non-conservative radiation induced force. This model is known to correctly describe experimentally observed trapped particle statistics for a wide range of physical parameters such as temperature and pressure. We theoretically analyse the effect of non-conservative force on the underlying steady state distribution as well as the power spectrum for the particle position. We compute perturbatively the probability distribution of the resulting non-equilibrium steady states for all dynamical regimes, underdamped through to overdamped and give expressions for the associated currents in phase space (position and velocity). We also give the spectral density of the trapped particle's position in all dynamical regimes and for any value of the non-conservative force. Signatures of the presence non-conservative forces are shown to be particularly strong for in the underdamped regime at low frequencies.

cond-mat.stat-mech↗