We have measured the temperature of a gas of sodium atoms released from "optical molasses" to be as low as 43±{}20 {μ}K. Surprisingly, this strongly violates the generally accepted theory of Doppler cooling which predicts a limit of 240 {μ}K. To determine the temperature we used several complementary measurements of the ballistic motion of atoms released from the molasses.
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Lett et al. (1988) studied this question.