Atom refrigerator
(a) To slow light, we need to create an ultracold cloud of atoms. Hot atoms emitted from the "candlestick" atomic-beam source are first decelerated by radiation pressure from the "slowing" laser beam in the 1 m long Zeeman slower. They are then loaded into the "optical molasses" a region in space created by six counter-propagating magneto-optical trap (MOT) laser beams (red). (The third pair, which goes in and out of the plane of the paper, is not shown.) After laser cooling the atoms to microkelvin temperatures, we turn the lasers off and load the atoms into the 4 Dee magnet, where they are "evaporatively cooled" to nanokelvin temperatures.
(b) The candlestick atomic-beam source, which we use to deliver sodium atoms to our experiments, works just like a candle. A gold-coated stainless-steel "wick" draws up atoms from a reservoir of liquid sodium at the base of a copper cylinder, guiding them to an emission hole in a hollow molybdenum cylinder that is filled with the stainless-steel mesh and placed inside the copper pot. At the hole, we create a localized hot spot at 350 °C, which leads to a high emission rate of sodium atoms. Only atoms that go through a small collimation hole in the copper cylinder escape into our set-up the rest hit the copper wall, which is also lined with stainless-steel mesh, and are transported back to the reservoir by a wicking action.