Transient trapping of two microparticles interacting with optical tweezers and cavitation bubbles

TL;DR

This study investigates how two absorbing microbeads can be temporarily trapped by optical tweezers, with cavitation bubbles influencing their trajectories and interaction times, revealing dynamics of multi-particle trapping.

Contribution

It demonstrates the transient trapping behavior of multiple absorbing particles and quantifies the timescales and probabilities of coalescence near the trap waist.

Findings

Two microbeads can briefly share the same optical trap.

Cavitation bubbles cause particles to be pushed away, affecting trajectories.

The coalescence times follow a Poisson exponential distribution.

Abstract

In this work we show that two absorbing microbeads can briefly share the same optical trap. Optical forces pull the particles towards the waist of the trapping beam. However, once a particle reaches the vicinity of the waist, the surrounding liquid is superheated creating an explosion or cavitation bubble that pushes the particle away while lengthening or shortening the trajectories of the surrounding particles. In this way each particle briefly interacts with the beam waist at different times. We find that when two microbeads reach the waist simultaneously, a larger explosion might result in ejection from the trap. We measure the characteristic timescale of two particle coalescence near the waist and find a Poisson decaying exponential probability distribution. The results are consistent with a simple simulation and show why the characteristic timescales for transient trapping of multiple absorbing particles decrease as more objects are added.