By Mike Martin
Forget fancy fuel cells -- laser light may be the fuel of the future for nanotech robots
"There are many beautiful designs for MEMs motors," said University of Chicago physics professor David Grier, "including electrostatic drives and magnetic drives. They all share the problem that they go a little bit slowly and they wear out very, very fast."
"We are able to show that light can spin nanotubes with ultra-high frequencies," Weizmann Science Institute chemical physicist Petr Kral wrote in a recent paper.
"Ultrafast frequencies -- tens of gigahertz -- are typical rotational frequencies in molecules and could be used to spin other molecules," paper co-author and Harvard physicist Hossein Sadeghpour told NewsFactor.
Lasers transfer the angular, or sideways, momentum of infrared photons to carbon nanotubes. The tubes then rotate like whirring turbines.
Scientists at the Department of Energy's Oak Ridge National Laboratory designed the first laser-driven nanomotor -- a cylindrical carbon tube surrounded by a carbon sleeve. In theory, applying an oscillating laser field would make the tube rotate enough to power a tiny motor, chemists Donald Noid and Bobby Sumpter and computer scientist Robert Tuzun explained in a groundbreaking 1995 paper.
"When we started to consider nanotechnology, we thought that a method would be required to use some form of energy that could create mechanical motion," Oak Ridge National Laboratory senior scientist Noid explained. "The most simple approach we could envision was that of rotation of nanotubes with lasers."
The Oak Ridge team only simulated a laser-powered nanomotor. The Harvard-Weizmann team says they have the blueprint for a working prototype.
From Nano to Micro
Tiny rings of light called "optical vortices" may produce enough angular momentum to power micro-electromechanical (MEMs) devices, say physics researchers David Grier and Jennifer Curtis, who presented their findings in the April 4, 2003, issue of the journal Physical Review Letters.
Micrometer-scale MEMs devices could help produce nanometer-size robots or laboratories-on-a-chip by bringing together silicon-based microelectronics with micromachining technology.
"One of the sticking points for these systems is the need for a motor," said Grier, a physics professor at the University of Chicago. "There are many beautiful designs for MEMs motors, including electrostatic drives and magnetic drives," he told NewsFactor. "They all share the problem that they go a little bit slowly and they wear out very, very fast."
Rings of Light
Optical vortices, however, have no moving parts, and friction will not slow them down.
"You can just project an optical vortex onto the device and away it will go," Grier explained.
Optical vortices are rings of light that can impart angular momentum to objects, making them spin. Photons -- individual packets of light -- already carry an intrinsic angular momentum, but the helical twist of an optical vortex adds an additional orbital angular momentum.
"That's what makes these optical vortices useful," Grier said.
An array of four vortices that can be configured into a 12-way pump fits into a space measuring five to 10 microns across, which is just a fraction of the width of a human hair, Grier explained.