Laser cooling

Laser cooling uses carefully tuned light to reduce the motion and temperature of atoms or ions. It relies on repeated interactions between particles and photons to remove kinetic energy.

Doppler cooling: A laser-cooling method that uses Doppler shifts to make moving atoms absorb photons that oppose their motion. It is the standard mechanism behind cooling atoms with red-detuned laser light.
Two-level atom: An idealized atom with only one ground state and one excited state available for interaction. It provides the simplest model for deriving the force and temperature of Doppler cooling.
Magneto-optical trap: A device that combines laser cooling and magnetic-field gradients to trap neutral atoms. It is a common apparatus for capturing and cooling atoms from a vapor.
Sideband cooling: A technique that cools trapped particles by driving transitions between motional quantum states and internal states. It can cool trapped ions or atoms below the Doppler limit by removing individual motional quanta.
Optical molasses: A configuration of intersecting red-detuned laser beams that slows atoms in three dimensions. Counterpropagating beams create velocity-dependent damping in Doppler cooling.
Radiation pressure: The force exerted when electromagnetic radiation transfers momentum to matter. Absorbed laser photons exert the directed force that slows moving atoms.
Optical dipole trap: A trap that confines neutral atoms through the dipole force from a focused, off-resonant laser beam. Laser-cooled atoms can be transferred into it for confinement without resonant scattering.
Evaporative cooling: A cooling method that lowers a sample's temperature by selectively removing its most energetic particles. It often follows laser cooling when the target temperature lies below laser-cooling limits.
Photon recoil: The momentum change an atom or other particle receives when it absorbs or emits a photon. Absorption and spontaneous emission transfer momentum, producing both cooling and residual heating.
Optical pumping: The redistribution of atomic populations among internal states through absorption and spontaneous emission of light. Cooling cycles often require pumping atoms back into a state that interacts with the laser.

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