= Optical molasses experiment of 1985
<Steven Chu>'s Bell Laboratories team prepared <sodium> atoms by pulsed-<laser> evaporation of a pellet. A frequency-swept opposing beam slowed them before six crossed <laser> beams supplied <optical molasses>. The <vacuum> chamber used a shield coated with <graphite> and cooled with liquid <nitrogen> as a pump. <Fluorescence> provided the readout; the initial beams were aligned as closely counterpropagating as possible. <The manipulation of neutral particles by Steven Chu>[Steven Chu, The manipulation of neutral particles, 1998 publication of his Nobel lecture, pp. 687–690, Figs. 3–4 and footnote 5: sodium source, precooling, vacuum apparatus, beam geometry and fluorescence detection]{ref}.
After equilibration, the team switched off the cooling <light> for a variable interval, then restored it. Faster atoms escaped during the dark interval; slower atoms were recaptured. The recaptured fraction versus delay constrained the <velocity> distribution and hence <temperature>. The inference depended on the initial cloud shape and recapture volume: <Steven Chu> later acknowledged adjusting a geometry correction towards the expected <Doppler cooling limit>. Delay was the scanned variable, and the cooling beams themselves supplied the release/recapture control; visible <fluorescence> alone could not establish <temperature>. <The manipulation of neutral particles by Steven Chu>[Steven Chu, The manipulation of neutral particles, p. 688, release-and-recapture paragraph: measurement sequence and retrospective account of the geometry correction]{ref}.
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