Monday, March 06, 2006

Long Days

Have I missed the weekend again? It just doens't feel like a weekend, is the problem. We worked yesterday.

Not an unsucessful day at work, actually, but to do anything these days takes longer and longer. First we have to turn on the cooling systems, and turn on, warm up, and tune the lasers. The tuning by itself can take all day, if we're unlucky.

Then align all the beams. This involves turning little screws on the back of the mirror mounts to change the angle. We have little targets set up to help us aim them correctly, irises which open when you're done with them to let the beams pass through. You have to start from the first mirror and go down the line, because if you're off by a small angle at the beginning, you'll miss mirrors entirely, toward the end. Also you have to make sure the beam is passing through all the different lenses and frequency shifters correctly. With so many beams and such long paths this always takes a couple of hours, and is tedious and repetative. If we have to change the beam paths for any reason, that can take an extra hour, or all day.

Parts of the beam are split off and sent through rubidium vapor cells, where, if they are at the right frequency, they are absorbed. We have electronics to adjust the lasers if the beam stops being absorbed (meaning that the laser frequency has drifted). But the electronics are complicated and don't always work. So getting that going can take a while too.

Meanwhile Ken has turned on the heaters that vaporize the rubium for the trap. Once everything is ready, assuming the vacuum pressure is okay, he opens the valve the releases the stream of rubidium vapor into the main vacuum chamber, and looks for a trap. He gets it every day now, reliably. But usually it starts out weak, and more alignment has to be done, and frequencies adjusted, before it will get big and bright.

Now we set up and mount any equipment we will be using for today's trial. Oscilloscopes, high voltage power supplies, light detectors, function generators, etc. Our post-doc does most of the electronic configuration. He's very good. We run lots of cables. More alignment, to make sure the light is getting onto the detectors.

Now, finally, we are ready to begin. We turn off the lights. (These detectors are sensetive. Room light could damage them.) I babysit my laser, changing the frequency when called upon, and making sure it doesn't change when it shouldn't. Ken babysits one of his lasers, and pours liquid nitrogen into the part of the vacuum system from time to time (this helps keep the pressure down.)

Lately his job also includes casting a shadow on the detector, which is picking up light sources we can't control. If he moves, it stops working.

Our post-doc watches the function generators and oscilloscopes and calls out instructions for us, parameters to change. Make this beam stronger. Make this beam weaker. Change the frequency. Scan the frequencies. Block this. Block that. Make the pulse longer. Make the delay shorter. He is looking for certain effects on the light the detector picks up. If he sees them, he saves a trace and calls us over to look.

Not every day is like this. Sometimes we are assigned other projects to work on. But this is the priority, and it always comes back to running this experiment in the trap.

Yesterday we saw an effect we were looking for -- two of our beams prevented one another from being absorbed by the rubidium in the trap. (This is supposed to be useful one day in making the basis elements of a quantum computer. If you don't exactly see how, join the club.)

Today... We get to do it all over again, probably.

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