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.


The ability of light to apply pressure to objects is known as radiation pressure, which was first postulated in 1619 and proven in 1900. This is the principle behind the solar sail, which uses light radiation pressure to move through space. A 2010 study by physicist Grover Swartzlander 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.

This study was published on December 2010 in 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 exhibits uniform motion.

The experiment began as computer models that suggested when light is incident on a tiny object shaped like a wing, a stable lift force is applied to the particle. 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 infrared laser light from underneath the chamber. Radiation pressure pushes the particles along the direction of propagation, this is called the scatter force, but the excitement came when the particles were forced to the side in a direction perpendicular to the direction of propagating light. The transverse force on the particles is the lift force. The researchers discovered not only that the rods experienced stable lift, but that, depending on refractive index, the rod could have up to two stable angles of attack it rotated to when exposed to the laser light. Symmetrical spheres tested did not exhibit this same lift effect.

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.

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