Opto-mechanical expulsion of individual micro-particles by laser-induced shockwave in air

TL;DR

This study quantifies the force exerted by laser-induced shockwaves on aerosol particles at distances up to 5.5 mm, demonstrating the clearing mechanism's effectiveness beyond the filament region for potential free-space optical communication applications.

Contribution

It provides the first quantitative measurement of shockwave forces on aerosol particles at significant distances from laser filaments.

Findings

Shockwave exerts 500 pN to 8 nN force on particles

Particles are expelled from optical traps at distances up to 5.5 mm

Laser power influences the magnitude of the force

Abstract

It was recently demonstrated that laser filamentation was able to generate an optically transparent channel through cloud and fog for free-space optical communications applications. However, no quantitative measurement of the interaction between the laser-induced shockwave and the aerosol particles was carried out so far, leaving the precise nature of the clearing mechanism up for discussion. A critical question was the maximum distance at which the filament could still act on the aerosol particle. Distances widely exceeding the filament diameter and its energy reservoir exclude other potential clearing effects like shattering or explosion by direct exposure to the laser. Here, we quantify the force exerted by the shockwave on a single aerosol microparticle. The force is measured by observing the ejection and displacement of the particle when trapped in an optical tweezer. We demonstrate that even for distances ranging from 1.5 mm to 5.5 mm away from the filament, thus widely exceeding the filamentary region, an acoustic force of 500 pN to 8 nN (depending on the initial laser power) acts on the aerosol particle and expels it away from the optical trap.