Entropy exchange in laser cooling

Abstract

It is usually presumed that spontaneous emission is necessary to remove the entropy lost by laser-cooled atoms. Here we show that the changes in the laser beams themselves constitute a sufficiently large reservoir of $N$ states accessible to the system that their entropy $S={k}_{B}\phantom{\rule{0.2em}{0ex}}\mathrm{ln}(N)$ is sufficient to absorb the entropy lost by the atoms in the cooling process. Proper choice of laser parameters could possibly produce cooling of atoms or molecules over a wide range of temperatures without spontaneous emission.