Today we spent most of the time reassembling the MOT. I took the remaining piece of our 20 g of Sr and cut it roughly in half. I flushed and was flowing argon through the sink when I did it but I didn’t bother to assemble a sealed system with the gloves this time. I set up 2 dishes with dodecane in them and transferred all of my Sr into one. Then I rinsed all the pieces in the second one before attempting to scrape at the oxide layer and placing them all in a glass vial.
While the MOT was down we replaced the ion gauge and put a blank with a metal gasket in place of the slower window. The purpose for this is so that we can cool it to try and collect as much oxide as possible when we evaporate it. Unfortunately, when I put the Sr in the MOT I was not thinking about the construction of the oven. The oven consists of an volume that is slightly smaller than the rest of the tube so that the plunger that hold the Sr in butts up against a small lip. The purpose of this is to keep Sr from diffusing out the back of the oven. I put in enough Sr that it didn’t all fit in the oven area and I started mashing it up against the lip. This prevented the flange blank at the back to not seal properly and I wasted 2 gaskets trying to figure out what was going on. Ultimately, some Sr had to be removed from the oven and the lip scraped with a sharp tool. Still the last gasket didn’t compress evenly for some reason. I couldn’t tell why, so I left the system pumping down overnight. When I left the pressure was at 1.39x10^-5 Torr. If it’s not significantly lower than that when I get in tomorrow morning I’ll vent the system again and see if I can get the gasket to sit better.
I heated up the vapor cell with just the windows first. When the windows were at 380 C the valve was at 188.7 C and the Sr cup was at 257 C. With the valve at 400 the cup was only at 280.8 C. Even though this should have been better than 10% absorption I used the cartridge heater to bring it up to ~312 C. Still, no absorption while scanning from 21698.22-21698.35 cm^-1 and .27 – .38 and .48-61. Either of the first 2 scans should have covered the line. Maybe tomorrow first thing I’ll check my estimate of what range I need to cover just to make sure. In the meantime, I tightened the swage connector between the cell and the pump and pumped on the cell again. I was going to cool the valve and see if I could get fluorescence at a higher temperature but I ran out of time. I closed the valves again including the right angle valve between the pump and the tee. Just to see if I tightened the swage enough I left the tee under vacuum and the pressure was at .79 Torr when I left which seems kind of high, but we’ll see if it gets close to atmosphere overnight.
First thing in the morning I’m going to see if I can get a signal at evaporation temperatures. If not I’ll have to figure out if we have a leak on the cell, or if the Sr has been compromised somehow. If I can’t solve the problem tomorrow I’ll probably move to the new double tee configuration. I should mention that for convenience I plugged the pump setup into the filtered power and the laser could not follow the doubling cavity for a full scan while the pumps were on. I don’t know yet if it was due to the vibrations of the pump or noise on the filtered line because I didn’t get to the point of switching the power for the setup, but we’ll find out tomorrow. It seems weird that it should be related at all because I’m pretty sure I’ve locked the laser with that setup running on filtered power before.
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