How does laser cooling work?

There's another physics of laser cooling in solid state which you do not talk about. This works by exciting atomic or excitonic transitions by using a laser that is just short of energy of this transition. In the process phonons from the material are absorbed and if the material has a high quantum efficiency, it gives out all of that energy as light which is higher in energy. We use this method to cool Yb3+ doped YLF crystals in our lab. This has also apparently worked for Cadmium sulfide semiconductor but although published in Nature it has not been reproduced yet.