A couple more pretty pictures of the apparatus, to pass the time:
This is the plasma discharge source that we use to make metastable atoms. We excite the gas using a RF coil (under the tinfoil) with a couple of watts of power at 145 MHz (local ham radio people must love me...), which creates a discharge in the glass tube. Some small fraction of the atoms are excited to the state that we want in the chaos of the plasma, and we work with those downstream.
When it's working right, there's a pretty steep pressure drop across the discharge region:
The pressure is much lower on the left (there's a honkin' big pump just out of the frame), which is why the color changes. Of course, if you screw up the valve settings, and let the pressure get too high all through the system, you get a kind of pretty effect:
Here you can see the discharge extending into the source chamber, because there's enough gas in there to keep it going. This is no good for the experiment, but it does look pretty cool.
And that should be enough pretty pictures to keep people occupied until I get back...
Comments
# 1 | xianli | March 24, 2008 3:19 PM
Steve mentioned your blog to me, and it is really good. The color of the charge is pretty, not like the xenon one (hard to see).
A dumb question, why do you use an RF induced plasma as a metastable source, instead of a high voltage discharge charge?
Do you use the similiar one for SAS to lock your laser?
# 2 | CCPhysicist | March 24, 2008 6:14 PM
Keep working and you will have that light saber real soon now!
# 3 | Josh | March 25, 2008 1:13 PM
purdy
# 4 | Chad Orzel | March 25, 2008 9:30 PM
xianli: A dumb question, why do you use an RF induced plasma as a metastable source, instead of a high voltage discharge charge?
It seemed a little simpler (no high voltage, and fewer fiddly bits inside the vacuum chamber), and Lu et al from Argonne seemed to suggest that it had a slightly higher efficiency than the high-voltage sort.
Do you use the similiar one for SAS to lock your laser?
Yeah, I have an RF coil driving a discharge in a cell that I bought from Joe Reader. It's actually been an enormous pain in the ass, because Kr seems to have a huge pressure broadening effect that screws up all the spectra.