Optical lift
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Optical lift is an optical analogue of aerodynamic lift, in which a cambered refractive object with differently shaped top and bottom surfaces experiences a stable transverse lift force when placed in a uniform stream of light.[1]
Discovery
Light has been known for some time to be capable of pushing objects and this is the principle behind the solar sail, which uses light to push vehicles along in outer space. Now, a 2010 study by physicist Grover Swatzlander and colleagues of the Rochester Institute of Technology in Rochester, New York shows light is also capable of creating the more complex force of "lift", which is the force generated by airfoils that make an airplane rise upwards as it travels forward. His study was published on December 2010 by Nature Photonics journal. Swartzlander predicted, observed and experimentally verified at a micrometer-scale that when applying a beam of laser light to a semi-cylindrical refractive rod, it automatically torques into a stable angle of attack, and then exhibit uniform motion.[1]
The experiment began as computer models that suggested when light is shone on tiny objects shaped like a wing, a stable lift force would be created. Then the researchers decided to do physical experiments in the laboratory, and they created tiny, transparent, micrometer-sized rods that were flat on one side and rounded on the other, rather like airplane wings. They immersed the lighfoils in water and bombarded them with 130 mW ultraviolet laser light from underneath the chamber. As predicted, the lightfoils were pushed upwards by the light, but they also moved sideways in a direction perpendicular to the beam of light. They discovered not only that the rods experienced stable lift, but that there were several angles that the rod tended to align itself to. Symmetrical spheres tested did not exhibit this same lift effect.[2]
In optical lift, created by a "lightfoil", the lift is created within the transparent object as light shines through it and is refracted by its inner surfaces. In the lightfoil rods a greater proportion of light leaves in a direction perpendicular to the beam and this side therefore experiences a larger radiation pressure and hence, lift.[2]
Potential uses
The 2010 discovery of stable optical lift is considered by some physicists to be "most surprising".[3] Unlike optical tweezers, an intensity gradient is not required to achieve a transverse force. Many rods may therefore be lifted simultaneously in a single quasi-uniform beam of light. Swartzlander and his team propose using optical lift to power micromachines, transport microscopic particles in a liquid, or to help on self-alignment and steering of solar sails,[3] a form of spacecraft propulsion for interstellar space travel.
Solar sails are generally designed to harness light to "push" a spacecraft, whereas Swartzlander designed their lightfoil to lift in a perpendicular direction; this is where the idea of being able to steer a future solar sail spacecraft may be applied.[4]
Swartzlander said the next step would be to test lightfoils in air and experiment with a variety of materials with different refractive properties, and with other wavelengths of light.[2]
See also
- Aerodynamic lift
- IKAROS - (Interplanetary Kite-craft Accelerated by Radiation Of the Sun)
- Laser propulsion
- Optical force
- Solar sail
References
- ^ a b Swartzlander Jr, Grover A. (05 December 2010). "Stable optical lift". Nature Photonics. doi:10.1038/nphoton.2010.266. Retrieved 2010-12-08.
{{cite journal}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b c Edwards, Lin (December 7, 2010). "Optical lifting demonstrated for the first time". Physorg. Retrieved 2010-12-09.
- ^ a b Palmer, Jason (8 December 2010). "'Lightfoil' idea shows light can provide lift". BBC News. Retrieved 2010-12-08.
- ^ Kaku, Michio (December 7, 2010). "Optical Lift May Allow Us to Steer Solar Sail Spacecrafts and Nano Devices". Big Think. Retrieved 2010-12-08.
External links
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