Dimensionality constraints of light induced rotation

TL;DR

This paper investigates the physical constraints on light-induced rotation without angular momentum transfer, revealing that permanent rotation requires specific 3D geometries or absorption, supported by theoretical, simulation, and experimental results.

Contribution

It provides a general condition for light-induced rotation, showing that lossless 2D or prism-like objects cannot rotate permanently under collimated light without angular momentum.

Findings

Permanent rotation is impossible for lossless 2D objects.

Partial absorption enables sustained rotation.

Experimental demonstration of a microscopic rotor.

Abstract

We have studied the conditions of rotation induced by collimated light carrying no angular momentum. Objects of different shapes and optical properties were examined in the nontrivial case where the rotation axis is perpendicular to the direction of light propagation. This geometry offers important advantages for application as it fundamentally broadens the possible practical arrangements to be realised. We found that collimated light cannot drive permanent rotation of 2D or prism-like 3D objects (i.e. fixed cross-sectional profile along the rotation axis) in the case of fully reflective or fully transparent materials. Based on both geometrical optics simulations and theoretical analysis, we derived a general condition for rotation induced by collimated light carrying no angular momentum valid for any arrangement: Permanent rotation is not possible if the scattering interaction is two-dimensional and lossless. In contrast, light induced rotation can be sustained if partial absorption is present or the object has specific true 3D geometry. We designed, simulated, fabricated, and experimentally tested a microscopic rotor capable of rotation around an axis perpendicular to the illuminating light.