How does laser cooling work? | Summary and Q&A

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March 30, 2016
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How does laser cooling work?

TL;DR

Laser cooling is a counter-intuitive process that uses lasers to slow down atoms and molecules by transferring momentum to them through photons.

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Key Insights

  • πŸ˜’ Laser cooling uses lasers to slow down the movement of atoms and molecules by transferring momentum through photons.
  • πŸ™‚ Light has both energy and momentum, and when atoms absorb photons moving in the opposite direction of their motion, their momentum is transferred, causing them to slow down.
  • πŸ™‚ Laser cooling requires specific wavelengths of light that atoms and molecules can absorb.
  • 🐒 Multiple lasers are used in different directions to slow down particles moving in any combination of those directions.
  • 😘 Laser cooling has been able to achieve extremely low temperatures, such as microkelvins, but absolute zero cannot be reached.

Transcript

Lasers make things hot. Just think of all the lasers in sci-fi-- laser guns, lasers shooting out of your eyes, laser cutting, burning tumors with lasers. And lasers can be used to burn your hair off. Hey, Derek from "Veritasium." Hey, Dianna from "Physics Girl." So there's one more interesting use of lasers. What's that? It's very different. Uh-huh... Read More

Questions & Answers

Q: How does laser cooling work?

Laser cooling works by using lasers to transfer momentum to atoms and molecules, slowing down their motion. Light carries momentum and when an atom absorbs a photon moving in the opposite direction of its motion, its momentum is transferred, causing it to slow down.

Q: Why does laser cooling seem counter-intuitive?

Laser cooling seems counter-intuitive because it involves adding energy (in the form of photons) to decrease the energy of the system. It is like trying to blow out a candle with a flamethrower. However, atoms and molecules constantly move in random motion, and pushing them in the opposite direction can slow them down.

Q: Do you need multiple lasers for laser cooling to work?

Yes, multiple lasers are used in different directions to slow down particles moving in any combination of those directions. Alternatively, three lasers and mirrors can be used on the other side to achieve the same effect.

Q: How cold can laser cooling get?

Scientists have been able to achieve temperatures as low as microkelvins (millionths of a degree above zero) using laser cooling. However, due to Heisenberg's uncertainty principle, which states that you can never precisely know the position and momentum of a particle at the same time, it is impossible to reach absolute zero.

Summary & Key Takeaways

  • Laser cooling is a technique that uses lasers to slow down the motion of atoms and molecules.

  • Light carries momentum in addition to energy, and when an atom absorbs a photon moving in the opposite direction of its motion, its momentum is transferred, causing it to slow down.

  • Multiple lasers are used in different directions to slow down particles moving in any combination of those directions.

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