Interference of the scattered vector light fields from two optically levitated nanoparticles

TL;DR

This paper experimentally demonstrates the interference of scattered vector light from two optically levitated nanoparticles in vacuum, revealing polarization-dependent fringe shifts and offering a method to measure their spatial separation.

Contribution

First experimental observation of interference of scattered vector light from two dipoles in free space, with implications for nanoparticle spatial measurement.

Findings

Interference fringes depend on dipole orientation.

Polarization vortex causes a π phase shift in fringes.

Method to determine nanoparticle separation using interference fringes.

Abstract

We experimentally study the interference of dipole scattered light from two optically levitated nanoparticles in vacuum, which present an environment free of particle-substrate interactions. We illuminate the two trapped nanoparticles with a linearly polarized probe beam orthogonal to the propagation of the trapping laser beams. The scattered light from the nanoparticles are collected by a high numerical aperture (NA) objective lens and imaged. The interference fringes from the scattered vector light for the different dipole orientations in image and Fourier space are observed. Especially, the interference fringes of two scattered light fields with polarization vortex show the {\pi} shift of the interference fringes between inside and outside the center region of the two nanoparticles in the image space. As far as we know, this is the first experimental observation of the interference of scattered vector light fields from two dipoles in free space. This work also provides a simple and direct method to determine the spatial scales between optically levitated nanoparticles by the interference fringes.