24 July 2024 | Xiaohao Xu, Manuel Nieto-Vesperinas, Yuan Zhou, Yanan Zhang, Manman Li, Francisco J. Rodriguez-Fortuño, Shaohui Yan & Baoli Yao
The article explores the existence of two fundamental torque components in optical manipulation: the gradient torque and the curl torque, which originate from the reactive helicity gradient and the momentum curl of light, respectively. These components represent the rotational analogues to the gradient and curl forces. The authors introduce the concept of lateral optical torques (LOT), which act transversely to the spin of illumination, and demonstrate that the orbital angular momentum of vortex beams can couple to the curl torque, potentially enabling extreme torque enhancement or achieving negative optical torques (NOT). The findings highlight the intersection between structured light, Mie-tronics, and rotational optomechanics, and suggest new avenues for manipulation in acoustics and hydrodynamics. The study also provides a multipole theory for optical torque, classifying it into three fundamental field properties: optical spin, reactive helicity gradient, and Poynting-momentum curl. The results are validated through numerical simulations and analytical models, showing that the LOT can be observed in both isotropic and anisotropic particles, and that the NOT can be achieved in single normal spheres by controlling the topological charge of the incident optical orbital angular momentum.The article explores the existence of two fundamental torque components in optical manipulation: the gradient torque and the curl torque, which originate from the reactive helicity gradient and the momentum curl of light, respectively. These components represent the rotational analogues to the gradient and curl forces. The authors introduce the concept of lateral optical torques (LOT), which act transversely to the spin of illumination, and demonstrate that the orbital angular momentum of vortex beams can couple to the curl torque, potentially enabling extreme torque enhancement or achieving negative optical torques (NOT). The findings highlight the intersection between structured light, Mie-tronics, and rotational optomechanics, and suggest new avenues for manipulation in acoustics and hydrodynamics. The study also provides a multipole theory for optical torque, classifying it into three fundamental field properties: optical spin, reactive helicity gradient, and Poynting-momentum curl. The results are validated through numerical simulations and analytical models, showing that the LOT can be observed in both isotropic and anisotropic particles, and that the NOT can be achieved in single normal spheres by controlling the topological charge of the incident optical orbital angular momentum.