Recoil temperature

In laser cooling, the Boltzmann constant times the recoil temperature is equal to the recoil energy deposited in a single atom initially at rest by the spontaneous emission of a single photon. The recoil temperature is In laser cooling, the Boltzmann constant times the recoil temperature is equal to the recoil energy deposited in a single atom initially at rest by the spontaneous emission of a single photon. The recoil temperature is T r e c o i l = ℏ 2 k 2 2 m k B {displaystyle T_{recoil}={frac {hbar ^{2}k^{2}}{2mk_{B}}}} , since the photon's momentum is p = ℏ k {displaystyle p=hbar k} (here k {displaystyle k} is the wavevector of the light, m {displaystyle m} is the mass of an atom, k B {displaystyle k_{B}} is Boltzmann's constant and ℏ {displaystyle hbar } is Planck's constant). The recoil temperature for the D2 lines of alkali atoms is typically on the order of 1 μK, and thus lower than the Doppler temperature. An example of a process where the recoil temperature can be reached is Sisyphus cooling.