Tuesday, February 13, 2007
We Have Liftoff
Click on the picture. Watch the animation. Then come back.
It's so hard to explain what this little animation means. Just know that it took years of blood sweat and tears to achieve it, mostly Ken's, but mine too, this last year or so. A lot of the saga I described here.
This is our magneto-optical trap. Being launched upward. The things on the sides are the magnetic coils that help hold it up. They are six centimeters in diameter, which should give you a sense of scale. We just need to be able to launch atoms a little bit higher than the top of the coils, because we can put our cavity right above them. This is the whole reason we designed these smaller coils, so that we wouldn't need to launch so high.
The atom cloud actually expands as it rises, out of the cooling beams. The beam we use to light it up so that we can see it is narrow, so you all you see is a narrow, pencil shaped slice out of the cloud as it expands, like the core of an apple. That's why it looks long and narrow toward the top.
These results don't mean we're done. First of all, we might want to cool the atoms a little more, so that they don't expand so much, so fast (although there is plenty of density up there, even as it is.) We are actually doing a slower launch, so that they slow to a halt just at the top of the coils and then fall back down. The slower launch takes longer, so the atom cloud has expanded more when it gets up there, which is why we might want the additional cooling. Also, we need a way to hold the atoms there, once we get them there. We already know how we're supposed to do that. It's called a "FORT" or "Far Off-Resonance Trap." It's easy in theory -- just shine a really strong, really tightly focused laser beam on the atoms, and that should hold them in place for the few milliseconds we need. Unfortunately we haven't made it work in practice yet, at least, not that we could detect. Finally, we need to actually build the cavity and put it in there. We've already built a couple of cavities for this thing, but for various reasons none of them is suitable for what we're trying to do now.
But still, that little blob in that animation looks a little bit like a light at the end of the tunnel.