A good writeup on the tech - https://spectrum.ieee.org/laser-cooling-chips

"The reemission is higher energy because it combines the energy from the incoming photons with phonons, vibrations in the crystal lattice of a material. This phenomenon is called anti-Stokes cooling, and it was first demonstrated in a solid back in 1995 when a team of scientists cooled an ytterbium-doped fluoride glass sample with laser light."