physics

Optical lift

Optical lift is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Optical lift rather than just read about it. In short: 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. Discovery The ability of light to apply pressure to objects is known as radiation pressure, which was first postulated in 1619 and proven in 1900.

Key takeaways

Optical lift belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Optical lift to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Optical lift from memory before moving on to harder problems.

Reference excerpt

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.

Discovery 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 in 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 lightfoils 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 the 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.

Potential uses The 2010 discovery of stable optical lift is considered by some physicists to be "most surprising". 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, 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.

See also Aerodynamic lift IKAROS – (Interplanetary Kite-craft Accelerated by Radiation of the Sun) Laser propulsion Optical force Solar sail

References

External links Video: Optical lifting demonstrated for the first time

Illustrations

Worked examples

Example 1 — a first encounter with Optical lift

Start with the simplest possible case. Write down what Optical lift claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Optical lift before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Optical lift ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Optical lift

In research: Optical lift appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Optical lift in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Optical lift is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aerospace engineering, Aircraft wing design, Force, so understanding it makes those chapters shorter.
In everyday life: Look for Optical lift outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Optical lift in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Optical lift means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Optical lift out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Optical lift in simple terms?

Why does Optical lift matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Optical lift?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Optical lift.