eli5 How does laser cooling work
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Things to know/remember beforehand:
* Temperature is the random motion/bouncing around of molecules and atoms
* Light gets absorbed by atoms when the particles of light (photons) matches very specific kinetic energies that depend on the atom they’re possibly getting absorbed by. This energy is directly related to the lights color (which is also it’s frequency and wavelength). Otherwise the light just passed through without doing anything
* If you are traveling towards the source of the light, you will see the light shift more “blue” (higher energy and frequency, shorter wavelength), opposite is true if you’re moving away. This is called Doppler shift
* When a photon gets absorbed by an atom, the momentum and energy of the photon gets transferred into the atom (conservation laws)
So, when scientists want to cool individual atoms with lasers, their goal is to slow down that random motion of the atom. What they do is set up a bunch of lasers that are tuned to emit light *just below* those absorption energies. This way, the light only gets absorbed when they’re moving towards each other (like a head on collision) because the light gets shifted into those energies to absorb. The energy is conserved by making the electrons jump to higher orbits around the atom, while the atom itself slows down to conserve momentum. This causes the atom to cool to as low as a few millionths of a degree above absolute zero
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