= Laser cooling
{wiki}
Laser cooling uses <laser> <light> to reduce the random <velocities> of <chemical atoms>, and therefore their translational <temperature>. The striking ingredient is selective <photon absorption>: an atom moving towards a beam sees a <Doppler shift> that can make it absorb more strongly. Each absorbed <photon> transfers <momentum> along the beam; repeated absorption and <spontaneous emission> can then remove <kinetic energy>. <Doppler cooling> makes this selection with the atom's motion, while <sub-Doppler cooling> also exploits its internal <quantum states>.
Cooling makes <chemical atoms> move slowly enough for longer interrogation in <atomic clocks> and <atom interferometry>, and easier loading into an <optical trap>. The same <radiation pressure> that pushes an atom can cool it: with suitably tuned opposing beams, whichever direction the atom moves, it receives the stronger push against that motion.
Back to article page
