Optical Tweezers with structured light and applications

Abstract

This thesis is a work about Optical Tweezers with structured light and their applications in the study of the dynamics and light-matter interactions of nano- and micro-scale colloidal particles. Optical Tweezers are invaluable scientific tools used to trap microscopic particles and originally consisted of a tightly focused laser beam exerting a gradient force on a polarizable object, hence the alternative name single-beam gradient force trap. Structured light is a generic term for light beams carrying a spatial structure of phase and polarization. In this thesis, we discuss the applications of vortex beams to study the dynamics of a particle embedded in a bistable potential, presenting a project that involved theoretical, experimental, and numerical results. Vortex beams are structured light fields that carry orbital angular momentum, which is encoded in a helical phase structure characterized by a topological charge. The bistable potential we present is a novel configuration for optical trapping systems employing vortex beam modes, and was first obtained from a numerical analysis and later confirmed experimentally. Additionally, we present the theory for optical forces using exotic beams composed of a combination of vortex modes, which results in a hybrid cylindrical vector and vortex beam. We discuss its application to the study of chiral light-chiral matter interactions and present a promising proposal for optical enantioseparation of Mie or dipolar particles using vector beams. The proposal is based on the fact that tightly focusing this family of exotic modes allows us to independently control different degrees of freedom of the field distribution by tweaking the input paraxial beam parameters.