Geometric phase self-focusing from optical spin angular momentum transfer to matter

Liquid crystals are well-known for their nonlinear orientational optical properties, in particular self-focusing as a result of optically induced reorientation magnitude, which relies on dynamic phase spatial modulation. Here we report on optical self-focusing of a purely geometric nature. The effect is demonstrated using a uniformly oriented liquid crystal half-wave plate illuminated by a fully polarized collimated beam. The effect is shown to be driven by spin angular momentum deposition and its magnitude scales with the amount of spin angular momentum carried by the incident beam. The experimental and modeling results encompass both material and wave aspects as well as the optomechanical process that drives the phenomenon, thus enriching the nonlinear spin-orbit photonics toolbox.