Typically, the source of neutral atoms for these experiments were thermal ovens which produced atoms at temperatures of a few hundred kelvins. The atoms from these oven sources are moving at hundred of meters per second. One of the major technical challenges in Doppler cooling was increasing the amount of time an atom can interact with the laser light. This challenge was overcome by the introduction of a Zeeman Slower. A Zeeman Slower uses a spatially varying magnetic field to maintain the relative energy spacing of the atomic transitions involved in Doppler cooling. This increases the amount of time the atom spends interacting with the laser light. Experiments can also use metal dispensers, which are pure metal (typically alkali metals) rods that can emit when heated up (the vapor pressure is higher) with electrical current.