Scientists have made a surprise discovery that lets lasers create jets streams inside a liquid. The process called ‘laser streaming’ is an observable phenomenon of lasers and fluids. Engineers from the University of Houston have discovered that highly focused lasers can transfer their momentum and create a stream of liquid.
Usually light passes through water with no effect on the liquid at all. But this new process forces the laser to interact with another medium which then allows it to ‘push’ the liquid creating a stream.
Lead researcher, Jiming Bao wrote in the published research, "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."
Bao and his fellow researchers used gold nanoparticles to help the laser push the liquid. To demonstrate the lasers new ability, they shone a pulsed green light into a container of liquids glass wall. Soon movement of the water within the container can be seen. A current of liquid is streaming in the same direction as the laser. "The flows appear as liquid analogues of laser beams and move in the same directions of the refracted beams as if they are directly driven by photons of laser beams. We call this phenomenon laser streaming” the scientists wrote.
The process works because the nanoparticles can absorb the green light as it resonates close to the frequency of the electrons. The particles heat up and then cool down with each pulse from the laser. Each change in temperature generates an acoustic wave, which in turn pushed the liquid forward. But this phenomenon called ‘acoustic streaming’ has been known about for some time. However, it does not guarantee liquid streaming. So the scientists pushed for a clearer answer. They discovered that the heating and cooling of the nanoparticles near the container wall caused them to bond with the glass. So over a period of time, the gold nanoparticles actually encrusted around the point of light entry on the container wall. This crust created a sort of nanocavity. This in turn actually acts as a sort of loudspeaker for the light, allowing it to be focussed to a point of always generated the stream.
The exciting discovery has a range of important applications. One area that will benefit the most is 'lab-on-a-chip' technology. This emerging area sees small chip biosensor chips that contain multiple functions which ordinarily would require a laboratory to analyze and interpret. The new device can be worn in a piece of wearable technology and analyze sweat or blood in order to detect multiple biomarkers linked to several diseases. Being able to move liquids at a microscopic scale is crucial to the fabrication of such devices. The technology could also be applied in nanofabrication and laser propulsion. Bao and his co-authors explain in their paper, "Laser streaming will find applications in optically controlled or activated devices such as microfluidics, laser propulsion, laser surgery and cleaning, mass transport or mixing, to name just a few."