Friday, March 30, 2007

Light can bend liquid

Physicists have used a laser beam to produce a surprisingly long and steady jet of soapy liquid that is narrower than a human hair.

The researchers were then able to push the liquid into a "hump-like shape", by directing the laser at a different angle.

The discovery was made by accident while University of Chicago fluid scientist, Wendy Zhang, was visiting colleagues at the University of Bordeaux in France.

Here, physicist Jean-Pierre Delville had observed a strange and unexpected result after completing a previous experiment studying the behaviour of fluid under a low intensity laser beam.

Delville then turned up the laser power just to see what it could do - what they found was that the laser beam was able to direct and bend the fine jet of liquid.

While heat can set liquid in motion, the researchers discovered that in this case it was the gentle radiation pressure generated by photons - discrete packets of light energy - that moved the fluid.

This radiation pressure is so slight it ordinarily goes unnoticed, but the liquid used in the Bordeaux experiment has such an "incredibly weak surface" that even light can deform it. "It's basically soap," Zhang said of the experimental liquid, which was a mixture of water and oil that had been precisely blended to display varying characteristics under certain conditions.

The find, which was further probed by lead author and Chicago graduate student Robert Schroll, is detailed in the 30 March edition of the journal Physical Review Letters.
Read more Light can bend liquid from Cosmos Magazine
Physicists Shine A Light, Produce Startling Liquid Jet from Science Daily
The life and death of a photon 'filmed' for the first time from CNRS

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