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The work volume contains a gas, at least part of which can be
condensed to a solid by cooling. It may be regular air with a little
humidity, below freezing point, or it may be a custom gas.
A laser of slightly below the resonant frequency of some of the gas
particles is focused where you want
material deposited. For
molecules moving towards the laser it is Doppler-shifted to
resonant frequency and hits the molecules, slowing them down.
For molecules moving away from the laser it is Doppler-shifted
away from the resonant frequency and doesn't hit the molecules.
It cools enough in that location that the condensable part of the
gas becomes solid and is deposited as intended.
The laser scans around to created the rest of the object.
For more information [Vernon, Aug 31 2011]
Animation of the laser Maxwell's demon gate
[sqeaketh the wheel, Aug 31 2011]
||Isn't Laser's significant in that they produce heat ?
||A similar 3d build up of condaste of liquids turned to solid material, is used in regular 'SLR' tech - (stereo litrophi resonance or so,), by pointing focus points into a bath of a raising layers of fixed material.
||While there IS a known "laser cooling" phenomenon that is exploited by researchers seeking ultra-cold atoms, I'm not sure that the mechanism described in the main text here is the same mechanism that those researchers use. I'm reasonably sure that just because a photon might not equal the resonant-frequency needed to be absorbed by a particle, in the spectrographic sense, that doesn't mean the photon can't interact with the particle some other way, such as by "scattering" --and if enough photons bounce off a particle, that particle may be heated, not cooled.
||There's an awesome article in one of the latest Scientific American's about using lasers to make a literal version of a Maxwell's demon gate trapping atoms one one side swapping entropy for information and release to cool things down close to absolute zero.
||Sorta related. Cool idea [caspian].
||Could you mix different gasses, and adjust the laser to switch gasses at will, in order to make something out of multiple materials? I want one in my garage.
||Thanks for the link Vernon. Doppler cooling on that page is
what I was thinking of. Looks like it works better for atoms
than molecules, and there's some more conditions I wasn't
aware of, so maybe some atoms aren't so selective about
photon frequency, and probably molecules aren't, but
otherwise I think my description matches.
||DIYMatt, good idea. I hadn't decided whether the directly
cooled particles had to be the ones deposited, or if other
particles would get indirectly cooled and deposited, but if
cooling different atoms will deposit them in particular
there are several laser options. I gather there are tunable
lasers. And also you can just have a second laser.
||sqeaketh, 2 fries, good link.
||What prevents the ink from boiling off the substrate
again after the laser leaves it? Maybe the ink reacts
chemically with either the substrate, or another ink
component, but only in the liquid phase?