Chiral optical tweezers for optically active particles in the T-matrix formalism

Francesco Patti,Paolo Denti,Rosalba Saija,Paolo Biagioni,Maria Antonia Iatì,Onofrio M Maragò,Giovanni Pellegrini

doi:10.1038/s41598-018-36434-9

Francesco Patti, Paolo Denti + Show 5 more

Open Access

https://doi.org/10.1038/s41598-018-36434-9

Copy DOI

Abstract

Modeling optical tweezers in the T-matrix formalism has been of key importance for accurate and efficient calculations of optical forces and their comparison with experiments. Here we extend this formalism to the modeling of chiral optomechanics and optical tweezers where chiral light is used for optical manipulation and trapping of optically active particles. We first use the Bohren decomposition to deal with the light scattering of chiral light on optically active particles. Thus, we show analytically that all the observables (cross sections, asymmetry parameters) are split into a helicity dependent and independent part and study a practical example of a complex resin particle with inner copper-coated stainless steel helices. Then, we apply this chiral T-matrix framework to optical tweezers where a tightly focused chiral field is used to trap an optically active spherical particle, calculate the chiral behaviour of optical trapping stiffnesses and their size scaling, and extend calculations to chiral nanowires and clusters of astrophysical interest. Such general light scattering framework opens perspectives for modeling optical forces on biological materials where optically active amino acids and carbohydrates are present.

Highlights

A chiral object is affected by the lack of symmetry under reflection[1]
In order to show the flexibility of the approach, we study two examples of chiral optical tweezers applied to anisotropic particles: a chiral nanowire and a particle cluster with properties that correspond to the amino acids discovered in the Murchison meteorite[35,37]
We explored the connection between optical activity and optical forces in a general light scattering framework

Summary

Introduction

A chiral object is affected by the lack of symmetry under reflection[1]. Both radiation and material objects may have this property. The mechanical interaction between chiral light and supramolecular chiral particles at the mesoscale has been studied with optical tweezers[7] investigating the optomechanics of cholesteric liquid crystals[25,26,27,28,29,30,31,32] (CLC). Their chiral properties result from the combination of birefringence[32] and a supramolecular multishell structure that yield a chiral band gap and radially directed Bragg reflections over a specific frequency range[25]. We study some practical examples, a complex resin particle with inner copper helices, the chiral optical trapping of optically active spherical particles, of a chiral nanowire, and of a particle cluster with optical properties corresponding to the amino acids discovered in the Murchison meteorite[35]

Methods

Results

Conclusion