Description du sujet de thèse

The dynamics of optically trapped scatterers in vacuum has emerged as a major topic, since roughly a decade. These latter are trapped in a light beam, and behave as Brownian (noisy) underdamped oscillator. Both fundamental questions (the route to the quantum ground state for macroscopic objects) and Applied Physics (force and torque sensors) are at stake.
In the recent years, our group has understood the influence of very weak non-conservative forces, and studied the torque transfer from the laser beam to matter. Nowadays, the Brownian dynamics of a 'small' levitating nano-object is well known, in the regime where thermal noise dominates.
Today, a main stake is to use heavier particles, so as to enhance the sensitivity of accelerometers and gyroscopes, especially in the low pressure limit, where laser intensity fluctuations dominate.

Objectives and planned work
This theoretical / numerical Ph-D will focus on the regime where the Brownian motion is driven by its (Poissonian) intensity fluctuations. Our goal is to trap more massive particles.
Both the trapping potential and the photon recoil damping will be controled through the multipolar scattering of the particle. To do this, we shall use spatially modulated wavefronts (implemented, e.g. with SLM technology), to encode specific phase lags between different multipolar contributions of optical forces.

Our preliminary results shows that modal engineering permits to optimize the beam in order to trap micrometric spherical particles. It is a breakthrough in vacuum levitodynamics, where, a regular tweezer beam can barely trap 150 nm particles.

The Ph-D shall propose single beam trapping designs for large particles, with a minimal Joule heating inside the material. Numerical Langevin simulation coupled to theoretical scattering models will be used, to understand the effect of photon noise on the dynamics of large particles. Tuning the scattering modes (e.g. their relative phase) will permit a new degree of control on the trapping potential as well as on the force noise, that were totally absent in the thermal regime.

Contexte de travail

The Ph-D will be hosted at LOMA, and benefit from the expertise of the Photonics team, and the help of several permanent researchers. He/she will have the opportunity to use several tools already developed in situ (numerical codes). The candidate will learn to work independently in a multidisciplinary environment, in collaboration with Physiscists (numerics + experimentalists).

Contraintes et risques

The Ph-D shall begin in 2025. The recruitment procedure shall end at the end of May 2025.
We look for a candidate with a master's degree in Physics, with strong interest and capabilities in nano-optics, willing to make numerical simulation. Knowledge of programming langages (e.g. Matlab) and numerical tools is a must. The candidate will work in close connection with an experimental group. Therefore, we seek a person with capabilities to work in a team, and who has good oral and written communications skills in English.

Informations complémentaires

J'ai traduit le texte.