Optical cycling paves the way for laser-cooled molecules

Laser cooling of atoms enables a great deal of ultracold physics. In its most widespread form, called Doppler cooling, a sample of atoms is irradiated from all sides with laser light whose frequency is tuned just below an atomic resonance. Each atom preferentially absorbs photons that are blueshifted into resonance - that is, the ones that oppose the atom's motion. The atom then reradiates the light in a random direction and returns to its ground state. Repeating that optical cycle some tens of thousands of times can cool the atomic sample to below 1 mK. © 2010 American Institute of Physics.