Characterization of periodic cavitation in an optical tweezer

TL;DR

This study characterizes the size, frequency, and lifetime of cavitation bubbles generated periodically in an optical tweezer, revealing bounds and empirical relations through high-speed imaging and photodiode measurements.

Contribution

It provides the first detailed measurement and analysis of cavitation bubble dynamics in optical tweezers, establishing bounds and empirical relations for bubble size, frequency, and lifetime.

Findings

Maximum bubble radius is bounded by microparticle size.

Most bubbles have radii between 2 and 6 micrometers.

Bubble lifetimes are at most twice the Rayleigh prediction.

Abstract

Microscopic vapor explosions or cavitation bubbles can be generated periodically in an optical tweezer with a microparticle that partially absorbs at the trapping laser wavelength. In this work we measure the size distribution and the production rate of cavitation bubbles for microparticles with a diameter of 3 $\mu$m using high speed video recording and a fast photodiode. We find that there is a lower bound for the maximum bubble radius $R_{max}\sim 2~\mu$m which can be explained in terms of the microparticle size. More than $94 \%$ of the measured $R_{max}$ are in the range between 2 and 6 $\mu$m, while the same percentage of the measured individual frequencies $f_i$ or production rates are between 10 and 200 Hz. The photodiode signal yields an upper bound for the lifetime of the bubbles, which is at most twice the value predicted by the Rayleigh equation. We also report empirical relations between $R_{max}$, $f_i$ and the bubble lifetimes.