In the microscopic world, a beam of light
carries enough force to move objects.
Researchers from St. Andrews University in Scotland have fashioned
a type of microgear with center slots that pick up the rotational momentum
from light, allowing the gears to rotate when illuminated by a type of
The devices could eventually be used to pump and mix extremely
small amounts of chemicals. The system of slots and polarized light could
also be used to make a diverse array of mechanical parts that can be rotated
or aligned using light, according to the researchers.
The slots change the amount that light bends as it enters the
gear, depending on its polarization. Light is polarized when its electric
field vibrates in one direction along the plane perpendicular to the direction
of the beam. Linearly polarized light that is oriented along the slots
bends more than light oriented across the slots. Light that bends more
applies a greater lateral force to the gear, causing the gear to line
up with the light's polarization.
When circularly polarized light strikes the parallel slots in
the gear, the light's rotational momentum is transferred to the gear.
The stronger the light beam, the faster the rotation.
Devices that use the gear system could become practical within
five years, according to the researchers. The work appeared in the June
19, 2005 issue of Nature Materials (All-Optical Control of Microfluidics
Components using form Birefringence).
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