Controlled transfer of transverse optical angular momentum to optically trapped birefringent particles

TL;DR

This paper demonstrates the transfer of transverse optical angular momentum to large birefringent particles in optical traps, enabling studies of complex fluid dynamics and cellular shear effects.

Contribution

It introduces a method for transferring transverse angular momentum to larger particles, expanding applications in micro-system studies and fluid dynamics analysis.

Findings

Quantitative measurement of transverse spin angular momentum transfer.

Generation of fluid flow around multiple rotation axes.

Observation of complex spin-orbit coupling effects.

Abstract

We report on the observation and measurement of the transfer of transverse angular momentum to birefringent particles several wavelengths in size. A trapped birefringent particle is much larger than the nano-particles systems for which transverse angular momentum was previously investigated. The larger birefringent particle interacts more strongly with both the trapping beam and fluid surrounding it. This technique could be used to transfer transverse angular momentum for studies of diverse micro-systems. Thus, it can be used for investigation of the dynamics of complex fluids in 3D as well as for shear on cell mono-layers. The trapping of such a particle with highly focused light is complex and can lead to the emergence of effects such as spin--orbit coupling. We estimate the transfer of spin angular momentum using Stokes measurements. We outline the physics behind the construction of the beam used to control the particles, perform quantitative measurement of transverse spin angular momentum transfer, as well as demonstrate the generation of fluid flow around multiple rotation axes.