Using optical tweezers to simultaneously trap, charge and measure the charge of a microparticle in air

TL;DR

This paper demonstrates how optical tweezers can be used to trap, charge, and measure the charge of a microparticle in air, revealing the laser's role in charging via a two-photon process.

Contribution

It introduces an experimental method to analyze laser-induced charging of particles in air using optical tweezers and a two-photon charging model.

Findings

Laser trapping can induce charge on a microparticle in air.

The charging process is accurately modeled as a two-photon process.

Experimental data aligns well with the two-photon charging model.

Abstract

Optical tweezers are widely used as a highly sensitive tool to measure forces on micron-scale particles. One such application is the measurement of the electric charge of a particle, which can be done with high precision in liquids, air, or vacuum. We experimentally investigate how the trapping laser itself can electrically charge such a particle, in our case a $\sim 1\,\mathrm{\mu m\;SiO_2}$ sphere in air. We model the charging mechanism as a two-photon process which reproduces the experimental data with high fidelity.