A vector holographic optical trap

Nkosiphile Bhebhe,Valeria Rodriguez-Fajardo,Andrew Forbes,Peter A C Williams,Carmelo Rosales-Guzmán

doi:10.1038/s41598-018-35889-0

Nkosiphile Bhebhe, Valeria Rodriguez-Fajardo + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-35889-0

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Abstract

The invention of optical tweezers almost forty years ago has triggered applications spanning multiple disciplines and has also found its way into commercial products. A major breakthrough came with the invention of holographic optical tweezers (HOTs), allowing simultaneous manipulation of many particles, traditionally done with arrays of scalar beams. Here we demonstrate a vector HOT with arrays of digitally controlled Higher-Order Poincaré Sphere (HOPS) beams. We employ a simple set-up using a spatial light modulator and show that each beam in the array can be manipulated independently and set to an arbitrary HOPS state, including replicating traditional scalar beam HOTs. We demonstrate trapping and tweezing with customized arrays of HOPS beams comprising scalar orbital angular momentum and cylindrical vector beams, including radially and azimuthally polarized beams simultaneously in the same trap. Our approach is general enough to be easily extended to arbitrary vector beams, could be implemented with fast refresh rates and will be of interest to the structured light and optical manipulation communities alike.

Highlights

The invention of optical tweezers almost forty years ago has triggered applications spanning multiple disciplines and has found its way into commercial products
A major breakthrough in optical manipulation techniques came from the field of structured light[21], especially the use of the Spatial Light Modulators (SLMs)[22,23] to produce holographic optical traps (HOTs)[24,25,26]
The generation methods have evolved from simple interferometric techniques, capable of generating only one vector beam, to more complicated configurations relying on spatial light modulators[43,45,46,47,48]

Summary

Introduction

The invention of optical tweezers almost forty years ago has triggered applications spanning multiple disciplines and has found its way into commercial products. Direct comparison of azimuthally and radially polarized vector beams has shown that the former features a stronger lateral trapping force compared to the latter[51,52] These topical beams are described by states on a generalized Poincaré Sphere[59,60], the so-called Higher-Order Poincaré Sphere (HOPS), to account for the total angular momentum of light, spin and angular[59]. Each HOPS beam in the array is independently controlled by an SLM and may be switched from scalar states (on the poles of the HOPS) to cylindrical vector vortex beams (on the equator of the HOPS) By this approach, we are able to tailor on-demand the 3D shape of the optical forces at specific locations inside the optical trap. To show the potential of this technique, we simultaneously compare the trapping strength www.nature.com/scientificreports/

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