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

TL;DR

This paper presents the first direct macroscopic observation of spin-dependent lateral forces and left-handed torques caused by structured light, revealing effects much larger than previously reported and expanding optical manipulation capabilities.

Contribution

It provides the first naked-eye evidence of macroscopic spin-dependent optical forces and torques, demonstrating their magnitude and potential for new optical manipulation techniques.

Findings

Observation of centimeter-sized objects displaced by spin-dependent lateral forces

Detection of left-handed macroscopic rotational motion due to optical torques

Optical force fields observed are five orders of magnitude larger than previous reports

Abstract

Observing and taming unusual effects arising from non-trivial light-matter interaction has always triggered scientists to better understand Nature and develop technological tools towards implementing novel applications. Recently, several unusual optomechanical effects have been unveiled when subtle spin-orbit interactions come at play to build up optical forces and torques that are hardly seen in everyday life, such as negative optical radiation pressure, transverse optical forces, or left-handed optical torques. To date, there are only a few experimental proposals to reveal these effects despite tremendous conceptual advances. In particular, spin-dependent lateral forces and their angular analog are done either at the expense of direct observations or at the cost of specific instrumental complexity. Here we report on naked-eye identification of light-induced spin-dependent lateral displacements of centimeter-sized objects endowed with structured birefringence. Its angular counterpart is also discussed and the observation of left-handed macroscopic rotational motion is reported. The unveiled effects are ultimately driven by lateral optical force fields that are five orders of magnitude larger than those reported so far. These results allow structured light-matter interaction to move from a scientific curiosity to a new asset for the existing multidisciplinary optical manipulation toolbox across length scales. In addition, this highlights the spin-orbit optomechanics of anisotropic and inhomogeneous media, which is just beginning to be explored.