Measurement of mass by optical forced oscillation of absorbing particles trapped in air

TL;DR

This paper presents a method to measure the mass of absorbing micro-particles trapped in air using optical forced oscillation, enabling particle classification based on density estimation.

Contribution

It introduces a novel optical forced oscillation technique to accurately determine the mass and density of micro-particles in air, aiding particle identification.

Findings

Mass measurement is achieved through forced oscillation amplitude analysis.

Optical trap stiffness varies linearly with light intensity.

Density estimates can classify different absorbing particles.

Abstract

We demonstrate the measurement of mass of the absorbing micro-particle trapped in air by optical forced oscillation. When the trapping light intensity is modulated sinusoidally, the particle in the trap undergoes forced oscillation and the amplitude of the oscillation depends directly on the modulated frequency. Based on a simple spring model, we fit the amplitudes versus the modulated frequencies and obtain the stiffness of the optical trap and the mass of the trapped particle. The fitting results show that, for a certain particle, the stiffness varies linearly with the trapping light intensity while the mass is consistent. The density of the micro-particle is then estimated and could be used to classify different kinds of absorbing particles, like C and CuO.