Doppler cooling limit

The Doppler temperature ( named after the physicist Christian Doppler) is the minimum temperature that can be reached by Doppler cooling of an atomic two - level system.

When a photon is absorbed by an atom, which moves in the opposite direction, the velocity of the atom is reduced due to the conservation of momentum. Similarly, an atom gains an additional pulse on the emission of a photon. However, since the spontaneous emission is isotropic, this pulse averages statistically zero. At the temperature at which the cooling compensates for the heating caused by the spontaneous emission, no further cooling is possible.

The Doppler is given by temperature with the inverse of the lifetime of the excited state, the Boltzmann 's constant, and the reduced Planck constant.

The emission and absorption by the Doppler effect depends on the critical speed.

The Doppler temperature is not the lowest achievable with laser cooling temperature. Using the polarization gradient cooling to temperatures can be achieved under the Doppler temperature ranging up to the theoretical limit the rebound temperature.

• Atomic physics
• Laser Physics
• Threshold value ( temperature)