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First Liquid-Cooling Laser Could Advance Biological Research (washington.edu)
Zothecula writes: In a world where lasers are sci-fi's weapon of choice for melting away an enemy spaceship, researchers at the University of Washington have swum against the current and produced the first laser capable of cooling liquids. " They demonstrated that the laser could refrigerate saline solution and cell culture media that are commonly used in genetic and molecular research. To achieve the breakthrough, the UW team used a material commonly found in commercial lasers but essentially ran the laser phenomenon in reverse. They illuminated a single microscopic crystal suspended in water with infrared laser light to excite a unique kind of glow that has slightly more energy than that amount of light absorbed. This higher-energy glow carries heat away from both the crystal and the water surrounding it." The technology could be especially useful for slowing down single cells and allowing scientists to study biological processes as they happen.
Aside from the science fiction spin of the summary, the ACTUAL science going on here is called an anti-Stokes shift. When light is absorbed and re-emitted, more commonly some of the light energy is converted to heat (phonons), resulting in the emitted light having slightly longer wavelength (Stokes shift). If there is a strong resonance in absorption at a particular wavelength, emitted light will tend to be closer to the resonant wavelength, even if the absorbed light is of lower energy and requires absorbing heat (a phonon) to generate the higher energy photon for emission.
https://en.wikipedia.org/wiki/Stokes_shift
FWIW, they've been doing laser-doppler cooling for a while (all the articles you hear about cooling atoms down near absolute zero generally used laser-doppler cooling). This anti-stokes technique is very similar to the laser-dopper cooling technique in that both involve on average the emission of photons at higher mean energy than those absorbed.
In the case of laser doppler cooling, you illuminate a batch of atoms with a laser from multiple directions at a slightly lower frequency than a transitional energy state. Atoms that are thermally in motion, but are instantaneously moving towards one of the lasers will absorb more photons (because doppler blue-shift makes the atom see the slightly higher frequency matching its transition energy state from the laser if it is moving towards from laser) causing the atom to lose net momentum in that direction and become slightly cooler (mostly because the photon will be re-emitted in a random direction).
In the case of the anti-stokes technique, you need to construct a system that has florescence (emits light a certain frequency when excited) with a bandgap, you then need to pump the energy into the system at the lower frequency. The trick (which is what makes this hard), is that the system needs to be tuned so that the energy you pump in is more efficiently converted into florescence energy than general thermal heating and the photons that are released by florescence can efficiently leave the system to avoid secondary heating.
Anti-stokes is interesting because it has the potential to be able to cool things microscopically (rather than at the atomic scale only).
AFAIKT, this team pulled out quite a few stops to setup this system. Apparently, they setup a laser trap to localize the florescent crystal (doped-YLF) and the "liquid" was D2O (deuterium or heavy water) to get the right thermal gradients for the laser trap for their experiment.
If you are interested, you can read about it here.