Game of Photons: Boffins make ICE with FIRE Laser refrigeration, that counter-intuitive application of the technology, has taken an important step towards reality, with scientists from the University of Washington chilling water by 36°F (20°C). That's enough of a change, in normal real-world conditions, for the research team led by assistant professor of materials …
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to freeze, flick switch down to burn.
Multi-pirpose 'ray gun, freezeray and burnray in one!
I see much rejoicing from the evil super-villains who can't decide whether it's more cool to be Mr Freeze or Mr Burn (or torch?), they can be both without having to carry around 2 guns.
If the principle is to slow a molecule down by hitting it with a photon, where does the energy go? (Direction is important for momentum but not energy, discuss).
Personally, I don't see any direct application of laser-cooling but the underlying principle of energy extraction may have legs.
As stated in the article, the energy escapes as photons with a slightly higher energy than the ones emitted by the laser, basically they bounce off the molecules moving towards the laser and, being light, what would normally result in a speed increase for a Newtonian collision translates as an energy increase for a photon.
About as efficient as braking a car by firing tennis balls at it I suspect.
As with all refrigeration, this is not some anti-entropic free lunch, lasers emit much more energy as waste heat than what leaves in the beam as coherent photons.
"Personally, I don't see any direct application of laser-cooling but the underlying principle of energy extraction may have legs."
Laser cooling can be used in situations where your standard cryogenic freezer or liquid helium just won't cut it i.e. to get materials down to temperatures below 4 Kelvin when you're investigating things like superconductivity and other quantum effects at fractions of a degree above absolute zero.
All sorts of weird and wonderful things happen at these temperatures, like atoms moving upwards in a gravitational field rather than downwards, or quantum gas temperature dipping just below absolute zero - yes, sounds impossible but that's quantum uncertainty for you...
Throwing in my explanation here as well.
It is basically down to the Doppler effect. Particles moving towards the light will perceive the light as a higher frequency. If the light has a slighter lower frequency than required for excite an electron then that increase will be enough for it to happen. When the electron later decays it will emit a photon of the same high frequency. So you have "low" energy photon meeting the particle and another "high" energy photon leaving some time later. That extra energy has to be taken from it's movement.
The Peltier effect used by small coolers is far more efficient than this laser chiller.
And that's not saying much as the transistor type coolers (Peltier) never won any energy awards.
Simple radiative heat exchange and refrigerants are still the best technology in cooler climates if naturally occurring chilled water (rivers, lakes, ocean) is not available. In low humidity areas like parts of the Middle East, (or semi-deserts anywhere) Evaporative Cooling (Swamp coolers) is best hands down. You can even use sea water if you need to. Cheap, easy to maintain and comprehend.
The applications for laser cooling and evaporative cooling are, shall we say, slightly different.
This is rather like complaining that carrying a book from one room to another is less efficient than sending a fleet of container ships to the other side of the planet.
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