Gradient and curl optical torques

Area of Science:

• Optomechanics
• Structured Light Physics
• Nanophotonics

Background:

• Optical forces and torques enable full manipulation of matter.
• Structured light has revealed gradient and curl forces, leading to phenomena like negative optical forces.
• Existing methods focus on translational motion, with rotational manipulation being less explored.

Purpose of the Study:

• To uncover fundamental components of optical torques.
• To introduce and demonstrate lateral optical torques.
• To explore the coupling of light's orbital angular momentum to torque for enhanced manipulation.

Main Methods:

• Theoretical analysis of light's reactive helicity gradient and momentum curl.
• Experimental demonstration of lateral optical torques using structured light.
• Investigation of vortex beams' interaction with optical torques.

Main Results:

• Identified two fundamental optical torque components: reactive helicity gradient torque and momentum curl torque.
• Demonstrated lateral optical torques acting transversely to light's spin.
• Showcased coupling between vortex beam orbital angular momentum and curl torque, enabling torque enhancement and negative torques.

Conclusions:

• The discovered torque components are rotational analogues to gradient and curl forces.
• Lateral optical torques offer new possibilities for transverse manipulation.
• This work bridges structured light, Mie-tronics, and rotational optomechanics, with potential applications in acoustics and hydrodynamics.