Imaging the dipole scattering of an optically levitated dielectric nanoparticle

TL;DR

This study experimentally visualizes the dipole scattering of an optically levitated nanoparticle in vacuum, revealing polarization-dependent scattering patterns and the formation of polarization vortices, advancing understanding of scattering anisotropy.

Contribution

We demonstrate direct imaging of dipole scattering from a levitated nanoparticle and analyze its polarization-dependent behavior using high NA microscopy, a novel approach in nanoparticle scattering studies.

Findings

Observation of dipole scattering with high signal-to-noise ratio.

Identification of polarization vortex formation when dipole aligns with optical axis.

Insights into scattering anisotropy and Kerker conditions.

Abstract

We experimentally observe the dipole scattering of a nanoparticle using a high numerical aperture (NA) imaging system. The optically levitated nanoparticle provides an environment free of particle-substrate interaction. We illuminate the silica nanoparticle in vacuum with a 532 nm laser beam orthogonally to the propagation direction of the 1064 nm trapping laser beam strongly focused by the same high NA objective used to collect the scattering, which results in a dark background and high signal-noise ratio. The dipole orientations of the nanoparticle induced by the linear polarization of the incident laser are studied by measuring the scattering light distribution in the image and the Fourier space (k-space) as we rotate the illuminating light polarization. The polarization vortex (vector beam) is observed for the special case, when the dipole orientation of the nanoparticle is aligned along the optical axis of the microscope objective. Our work offers an important platform for studying the scattering anisotropy with Kerker conditions.