Understanding and controlling colloidal interactions is very important in soft matter physics and its applications. In this context, optical forces are particularly interesting: first postulated by Kepler in 1619, they not only enable the trapping of particles, as demonstrated by Ashkin’s work on optical tweezers (2018 Nobel Prize in Physics), but also, when acting on several objects simultaneously, give rise to collective interactions. More precisely, it has been shown both theoretically and experimentally that dispersion forces between pairs of colloidal particles can be controlled using artificial random light fields.
After introducing the methodology for calculating optical forces in both deterministic and random fields using the coupled electric and magnetic dipole method, this doctoral thesis focused on the study of random field induced interactions for different numbers of particles. First, interactions induced by a random field on a particle in a structured medium were found to be proportional to the local density of states in that medium. Secondly, for systems made of two particles, the tailoring of the spectral energy density of the field was shown to allow the generation of pair potentials of different relevant shapes, as well as the creation of purely many-body interactions by making them vanish. Finally, interactions among N particles were investigated, making it possible to identify which approximations remain valid when studying larger and more realistic systems.