Recoil temperature

In quantum optics, the recoil temperature or Recoil temperature is the lowest temperature that can be achieved when particles are cooled by absorption and emission of photons ( such as atoms ) (also known as the recoil limit). It is defined as the temperature which can be assigned to a stationary atom emits exactly one photon on the cooling transition used, and thus a small momentum transfer ( recoil ) experiences.

The emitted photon has the momentum of the atom (h: Planck's constant, λ: wavelength of the photon, k = 2π / λ: wave number ). Due to conservation of momentum the atom receives an exactly opposite thereto pulse. If the atom has the mass, it follows from this change in momentum of the kinetic energy. This kinetic energy can now formally be assigned a temperature, the recoil temperature:

In this case, kB is the Boltzmann constant. The recoil temperature typically has a magnitude of 1 μK and is thus much lower than the Doppler temperature. The recoil temperature can be achieved for example by the method of Sisyphuskühlens.

Recoil speed

Analogous to the temperature, the recoil or rebound velocity recoil velocity is defined as that velocity vrecoil change experienced by an atom at the spontaneous emission of a photon:

It typically is a few cm / s