transforming laser beam into a flow of liquid
Researchers at the University of Houston studying the nonlinear transmission of light through an aqueous suspension of gold nanoparticles. The study is an unexpected discovery. A laser pulse appeared to force the movement of a stream of liquid in a glass laboratory cuvette, a type of glass test tube.
“It was not so simple,” said Jiming Bao, associate professor of electrical and computer engineering at the University of Houston. The momentum from a laser isn’t strong enough to activate the movement.
Light usually passes straight through the water without any absorption and scattering, even strong momentum from the photons wouldn’t generates a liquid stream. Researchers said, the gold nanoparticles turned out to be key.
The nanoparticles needed to create the stream because they reacted to focused laser pulse to create a plasmonic-acoustic cavity. The structure called as “bowl” that formed on the inner wall of the cuvette.
The moving stream of liquid triggered by ultrasound waves generated by the expansion and contraction of the nanoparticles. Which occurs when nanoparticles on the cavity surface heat up and cool down with each laser pulse. Once a cavity created, the nanoparticles removed. The streaming can move in any fluid.
The discovery has the potential to significantly improve work in several fields, including lab-on-a-chip experiments involving moving liquids.
The driving flow of the acoustic wave called acoustic streaming, widely used in microfluidics. The generation of ultrasound by gold nanoparticles called photo acoustics, used in bio-medical imaging.
new optofluidic principle
This new optofluidic principle couples photo acoustics with acoustic streaming. It generates high-speed flows inside any liquids without any chemical additives and apparent visible moving mechanical parts. The speed, direction and size of the flow controlled by the laser.
Bao said, to study better understanding how the gold nanoparticles form the plasmonic-acoustic cavity to determine better ways to generate a liquid stream, among other things.
The researchers conclude, laser streaming find applications in optically controlled or activated devices, such as microfluidics, laser propulsion, laser surgery and cleaning, mass transport or mixing.
More information: [ScienceAdvances]