Optical lift
Encyclopedia
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
.
, 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 airfoil
s 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.
, 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, 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.
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 incoherent light.
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
analogue of aerodynamic lift, in which a cambered
Camber (aerodynamics)
Camber, in aeronautics and aeronautical engineering, is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetric aerofoil...
refractive object with differently shaped top and bottom surfaces experiences a stable transverse lift force when placed in a uniform stream of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
.
Discovery
The ability of light to apply pressure to objects has been known for some time. This is the principle behind the solar sailSolar sail
Solar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....
, which uses light radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
to move through space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
. A 2010 study by physicist Grover Swartzlander and colleagues of the Rochester Institute of Technology
Rochester Institute of Technology
The Rochester Institute of Technology is a private university, located within the town of Henrietta in metropolitan Rochester, New York, United States...
in Rochester, New York shows light is also capable of creating the more complex force of "lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
", which is the force generated by airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
s that make an airplane rise upwards as it travels forward. This study was published on December 2010 in Nature Photonics
Nature Photonics
Nature Photonics is a peer-reviewed scientific journal published by the Nature Publishing Group. The journal covers research related to optoelectronics, laser science, imaging, communications, and other aspects of photonics and was established in January 2007...
journal. Swartzlander predicted, observed and experimentally verified at a micrometer-scale that when applying a beam of laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
light to a semi-cylindrical refractive rod, it automatically torques into a stable angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, and then exhibits uniform motion
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
.
The experiment began as computer models that suggested when light is incident on a tiny object shaped like a wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
, 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
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
laser light from underneath the chamber. Radiation pressure
Radiation pressure
Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...
pushes the particles along the direction of propagation, this is called the scatter force
Optical tweezers
Optical tweezers are scientific instruments that use a highly focused laser beam to provide an attractive or repulsive force , depending on the refractive index mismatch to physically hold and move microscopic dielectric objects...
, 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
Refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
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.
Potential uses
The 2010 discovery of stable optical lift is considered by some physicists to be "most surprising". Unlike optical tweezersOptical tweezers
Optical tweezers are scientific instruments that use a highly focused laser beam to provide an attractive or repulsive force , depending on the refractive index mismatch to physically hold and move microscopic dielectric objects...
, 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, a form of spacecraft propulsion
Spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
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.
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 incoherent light.
See also
- Aerodynamic lift
- IKAROSIKAROSIKAROS is a Japan Aerospace Exploration Agency experimental spacecraft. The spacecraft was launched on 21 May, 2010, aboard an H-IIA rocket, together with the Akatsuki probe and four other small spacecraft...
- (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) - Laser propulsionLaser propulsionLaser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass...
- Optical forceOptical forceThe optical force is a phenomenon whereby beams of light can attract and repel each other. The force acts along an axis which is perpendicular to the light beams. Because of this, parallel beams can be induced to converge or diverge. The optical force works on a microscopic scale, and cannot...
- Solar sailSolar sailSolar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....