Laser Streaming: Turning a Laser Beam into a Flow of Liquid

TL;DR

This paper introduces a novel optofluidic method that converts a pulsed laser beam into a steady water flow via a self-fabricated plasmonic cavity, driven by photoacoustic streaming, with broad potential applications.

Contribution

It reveals a new principle of laser-driven fluid flow through photoacoustic effects and demonstrates a self-fabricated cavity enabling this process in pure water.

Findings

Steady water flow generated by pulsed laser in pure water.

Flow driven via ultrasound resonantly generated by laser.

Principle applicable to various liquids for optofluidic applications.

Abstract

Transforming a laser beam into a mass flow has been a challenge both scientifically and technologically. Here we report the discovery of a new optofluidics principle and demonstrate the generation of a steady-state water flow by a pulsed laser beam through a glass window. In order to generate a flow or stream in the same path as the refracted laser beam in pure water from an arbitrary spot on the window, we first fill a glass cuvette with an aqueous solution of Au nanoparticles. A flow will emerge from the focused laser spot on the window after the laser is turned on for a few to tens of minutes, the flow remains after the colloidal solution is completely replaced by pure water. Microscopically, this transformation is made possible by an underlying plasmonic nanoparticle-decorated cavity which is self-fabricated on the glass by nanoparticle-assisted laser etching and exhibits size and shape uniquely tailored to the incident beam profile. Hydrophone signals indicate that the flow is driven via acoustic streaming by a long-lasting ultrasound wave that is resonantly generated by the laser and the cavity through the photoacoustic effect. The principle of this light-driven flow via ultrasound, i.e. photoacoustic streaming by coupling photoacoustics to acoustic streaming, is general and can be applied to any liquids, opening up new research and applications in optofluidics as well as traditional photoacoustics and acoustic streaming.