Macroscopic direct observation of optical spin-dependent lateral forces and left-handed torques

Observing and taming the effects arising from non-trivial light–matter interaction has always triggered scientists to better understand nature and develop photonic technologies. However, despite tremendous conceptual advances^1,2, so far there have been only a few experimental proposals to reveal unusual optomechanical manifestations that are hardly seen in everyday life, such as negative radiation pressure^3,4, transverse forces^5,6 or left-handed torques⁷. Here, we report naked-eye identification of spin-dependent lateral displacements of centimetre-sized objects endowed with structured birefringence. Left-handed macroscopic rotational motion is also reported. The unveiled effects ultimately rely on spin–orbit optical interactions and are driven by lateral force fields that are five orders of magnitude larger than those reported previously, as a result of the proposed design. By highlighting the spin–orbit optomechanics of anisotropic and inhomogeneous media, these results allow structured light–matter interaction to move from a scientific curiosity to a new asset for the optical manipulation toolbox.