What is "evaporative cooling"

n. (context physics English) The cooling of a liquid due to the removal of the faster-moving molecules by evaporation from its surface

Evaporative cooling is an atomic physics technique to achieve high phase space densities which optical cooling techniques typically can not reach.

Atoms trapped in optical or magnetic traps are cooled as the trap depth is decreased and the hottest atoms (with the highest kinetic energy) leave the trap. The hot atoms leaving the trap are on the tail of the Maxwell-Boltzmann distribution and therefore carry away a significant amount of kinetic energy, mitigating the loss of atoms by an overall increase in phase space density. The technique is analogous to cooling a hot cup of coffee by blowing on it.