Unexpected Laser Discovery Leads to New 'Optofluidics' Principle

University of Houston  researchers, studying the nonlinear transmission of light through an aqueous suspension of gold nanoparticles, noticed something unexpected. A pulse laser appeared to have forced the movement of a stream of liquid in a glass laboratory test tube. As they investigated, they realized something more complex was a work than a transfer of momentum from the laser photons to the liquid. Their observation led to a new optofluidics principle, and the discovery has the potential to significantly improve work in a number of fields, including lab-on-a-chip experiments involving moving liquids, such as a droplet of blood, at a microscopic scale.

Transcript

00:00:00 how to generate a jet flow with laser beam imagine use the laser to drive water flow along the same direction first we need to add some code nanoparticle note that the code nanoparticle appears right here because they can strongly absorb green light to better see the flow we also add some reference fair as tracing particles and use a red laser to illuminate them take

00:00:31 an overview of the experiment setup then let's see what will happen laser is new Siddhant from the right to left the bright spot is a focused laser on the inner wall of the glass cue wet high-speed and the steady flow can be created when the camera is moved to the back side of the cue wet we can see the flow hitting the back wall of the cue wet well so jet is created we can remove

00:01:03 the nanoparticles and fill the qubit with fresh water now a jet flow can be generated also in water for other kind of liquids then we have to ask this question how can they sir dry watch it flow this is a unique combination of two well-established principles first is a photo acoustic effect under post laser irradiation gold nano particles will experience rapid a thermal expansion

00:01:36 will absorb in the laser and then construction when the laser is off therefore generating high-frequency ultrasound the technique has been widely used in biological imaging the second principle is acoustic streaming discovered by scientists Faraday now people use the ultrasound transducer instead of mechanical pump to travel liquid flow

00:02:05 the technique is more important for micro fluidics because it is difficult to fabricate micro sized pump well laser is focused on the q''-word wall with Scott nano particles suspended in the water the working a little like cavity is created from the inner surface of the wall and nanoparticles become attached to the cavity surface here we introduce a new opto flow index principle laser

00:02:38 streaming or we can call photo acoustic streaming which is a dynamic combination of photo acoustics and acoustic streaming