What is Laser Cooling?
Laser cooling is a method of slowing down atoms, and thus cooling them, using lasers. Typically we view lasers as heating things up, and they certainly do on macroscopic scales, but for individual atoms or small groups of atoms, they can be used for cooling. The coldest temperatures ever generated, less than half a billionth of a Kelvin (0.5 nanoKelvins) have been achieved by using a combination of laser cooling and evaporative cooling. These temperatures are achieved with tiny amounts of diffuse gases. The primary mechanism by which laser cooling slows down atoms is by causing them to absorb and emit photons in random directions. As long as the velocity of the atom is greater than the recoil velocity of photon emission, the overall velocity is reduced. If you were floating on a hovercraft, moving a significant velocity in one direction, and randomly threw metallic balls off the hovercraft, eventually your velocity would slow down and your movements would entirely be dictated by the re
