Observation of Atoms Laser Cooled below the Doppler Limit

Abstract

We have measured the temperature of a gas of sodium atoms released from "optical molasses" to be as low as 43\ifmmode\pm\else\textpm\fi{}20 \ensuremath{\mu}K. Surprisingly, this strongly violates the generally accepted theory of Doppler cooling which predicts a limit of 240 \ensuremath{\mu}K. To determine the temperature we used several complementary measurements of the ballistic motion of atoms released from the molasses.