Wednesday, December 20, 2006

Good MOT, Good MOT!

Okay, so remember the other day when I said we had the brightest trap ever, but couldn't get it to work when we changed the set-up? And how if we didn't change the set-up, we couldn't do the experiment? So we really needed to get it working with the new set-up? Well, we did!

I promised pictures of the super-bright trap, and I took them, just didn't get around to uploading them. But now you can see the super-bright trap, and the new-set-up trap.

But first, for reference, is a picture of what the trap used to always look like (on a good day)

Second is a picture I took of the same monitor, with the same camera (though the camera had been moved slightly, but not significantly closer) on the day after we saw the trap with the naked eye. Believe it or not, the trap was actually even bigger than this at one point, though not much bigger.

The final picture is the trap we got today. It was also slightly bigger than this at one point, but this was a better photo. As you can see, even the weaker new trap is brighter than the kind of trap we used to get.

It always feels like a lot of lot of work to get back to the same place, when we're trying to get the trap going again. This time it took weeks. But the truth is, this represents a major step forward. Because we changed the configuration of the laser beams, and this trap, unlike the old one, can be launched upwards.

The theory behind a trap requires six laser beams: one pointing up, one pointing down, one pointing left, one pointing right, one pointing forward, and one pointing backward. (Actually, our trap is rotated a little so that some beams are diagonal, but lets just ignore that and talk about up and down, forward and back, and left and right.) Up until now, the left pushing beam was simply a reflection of the right pushing beam, and the doward pushing beam was a reflection of the upward pushing beam, and so on. But if you can change the frequencies a little, so that the upward pushing beam is a little higher in frequency than the doward pushing beam, you can arrange for the upward beam to push a little harder than the downward beam... And the atoms are launched upward. It's called an "atomic fountain." This is a necessary part of Ken's experiment. But you can't do it if the downward beam is simply a reflection of the upward beam -- then they're automatically the same frequency.

However, the downward beam is a reflection no more, but a completely independent beam whose frequency can be independently changed. Another hurdle cleared. The impossible experiment is still on.

And we can go on Christmas break without this frustration hanging over our heads.

It feels good.

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