Doppler cooling

Photons accept a drive accustomed by ħk (where ħ is the bargain Planck connected and k the photon wavenumber), which is conserved in all atom-photon interactions. Thus, if an atom absorbs a photon, it is accustomed a drive bang in the administration of the photon afore absorption. By detuning a laser axle to a abundance beneath than the beating abundance (also accepted as red detuning), laser ablaze is alone captivated if the ablaze is abundance up-shifted by the Doppler effect; which occurs whenever the atom is affective appear the laser source. This applies a abrasion force to the atom whenever it moves appear a laser source.

For cooling to action forth in all directions, the atom have to see this abrasion force forth all 3 cartesian axis; this is a lot of calmly accomplished by anecdotic the atom with 3 erect laser beams, which are again reflected aback forth the aforementioned direction.