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On laser cooling: > Very basically what they did was use a specially tuned array of lasers to bombard the atoms with photons from all angles. These photons are
by sasaf5 6y ago
On laser cooling:
> Very basically what they did was use a specially tuned array of lasers to bombard the atoms with photons from all angles. These photons are like pingpong balls compared to the bowling-ball-like atoms, but if you have enough of them, they can arrest the motion of the cesium atoms, slowing them from about 130 meters per second to a few centimeters per second
Such a cool idea deserves a better brief explanation:
Atoms absorb light in a specific frequency, and are pushed by it. If your light is at a slightly lower frequency, due to doppler effect only atoms that are moving towards you will absorb and be slowed down. Atoms going in other directions will be undisturbed. The net effect is a reduction of movement, hence cooling.
- Ecco 6y agoOh wow, neat explanation, thanks! For some reason I always thought laser cooling was about “cornering” atoms in between laser beams. But then apparently from your explanation it’s really only about finding the right laser color! Then you can beam it in pretty much any direction and it will result in a global reduction of the speed of atoms (aka temperature). Did I get that right?
- sasaf5 6y agoYes that's the general idea. Lasers are used because of their temporal coherence (i.e. they shine in a single, stable, frequency).
- willis936 6y agoA critical part of a laser is coherency: all energy is at the same frequency and phase. This is really what sets laser light apart from other kinds of light and what makes it such a useful science tool.
- fsh 6y agoLaser cooling only reduces the velocity component that is directed against the direction of the laser beam. For free atoms you therefore need three pairs of counter-propagating beams to achieve overall cooling. If the atoms are somehow confined (for example ions in a trap), their motion has to reverse periodically and a single cooling beam can be enough.
- stan_rogers 6y agoBill Phillips (a NIST type who's also a Nobel laureate) gave a lecture called "Time, Einstein, and the Coolest Stuff in the Universe" at several locations a few years ago, and there are various videos of it online. It explains things rather thoroughly, and is a great example of an enthusiastic scientist going full nerd, including several classes of really bad jokes, etc. Worth a Google and a watch. If you can find the one he did in Toronto, that's probably the best one, but TVO (our provincial public broadcaster in Ontario) doesn't seem to have it up on their YouTube channel anymore.