Atomic Optics Uses Light To Focus Atom Beams

dcshoes writes: "Nonlinear Atom Optics uses laser light to cool atoms to one millionth a degree Kalvin. At this low temperature, atom wavelengths are elongated, making the wave nature of atoms more easy to observe, and enable scientists to focus, reflect, defract, etc, atom beams. Atom lasers could lead to advances in, among other things, Nanolithography and Holography. Cool. Literally."

Comments

Laser Cooling

[Muerte23]

Laser cooling is an application of using the Doppler shift to selectively absorb photons propagating counter to the direction of the atom's movement. The laser is slighty red-detuned from some spectral line of the atom, so when the atom moves towards the laser, it absorbs a now correctly blue-shifted photon and gets a kick of momentum to slow it down. Since the atom emits the photon again in a random direction, then net result after millions of collisions is to slow its net velocity to zero.

Since the atom is also emitting photons in random directions, it settles down to a minimum kinetic energy / temperature of about 240 microKelvin (for Sodium, for example). To cool atoms furter, you have to add in magnetic traps, then selectively "heat" the hottest atoms with RF energy to "boil" off the highest part of the temperature distribution to result in a lower average temperature of the condensate.

Check the MIT Center for UltraCold Atoms for more details.

Muerte

Re:cooling with a laser?

[Wind_Walker]

Basically, this is how you cool with lasers: Imagine you have six lasers, all pointed at the same place, and all in perpendicular directions (imagine a cube with a laser pointing directly at the center of each face, but the cube is actually transparent, the laser beams oriented towards each other)

Now we put some amount of mass right at the point where the 6 laser beams cross. The mass at the center will be hit by some photons from one of the lasers (for argument's sake). This will cause the mass to absorb the momentum of the photon, as well as excite the particle. The excited particle will then emit another photon in a random direction. However, there will be some recoil from this photon being ejected. Instead of being pushed away by this ejection, the particle is "persuaded" by the other lasers to stick around, so to speak. The process then repeats, but it takes about 10 minutes. Since the particle has lost momentum (to the ejected photon) it has less energy (in the Physics department here, we call it "tired").

Eventually, the mass at the center gets so "tired" that it falls into a quantum state of relaxation, as described by Schroedinger's equation and its wavefunction. Interesting things happen when it gets incredibly cold, and that's what the article is talking about. This was a very simplistic explanation, so if you want something more, just head over to Google and search for "laser cooling".

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That's just the way it is