Laser cooling of atoms by collisional redistribution of fluorescence

The general idea that optical radiation may cool matter was put forward by Pringsheim already in 1929 [1]. Doppler cooling of dilute atomic gases is an extremely successful application of this concept, and more recently anti-Stokes fluorescence cooling in multilevel systems has been explored [2], culminating in the optical refrigeration of solids. Collisional redistribution of fluorescence is a proposed different cooling mechanism that involves atomic two-level systems [3], though experimental investigations in gases with moderate density have so far not reached the cooling regime.