Research Update June 9 & 10th

Frustrated while looking for the saturated absorption signal in the cell. Despite differing levels of absorption and laser intensity we could not find a lamb dip with the probe laser. We did however work out that to get the right laser frequency, whether we shift the probe or the pump, the aom needs to be upshifting the frequency either way.

On top of that the etalon from the cell is horrible. Blah. The etaloning was getting worse throughout the time we were working with the cell. When we looked at transmittance through the cell we were getting 50%. We left the windows baking overnight with the rest of the cell cold and transmittance was slightly worse than 50% in the morning. After cooling down the cell, we unwrapped a window and could visibly notice some darkening of the windows and also that the copper had been affected by the strontium.

We ordered sapphire windows and silver coated gaskets to refurbish the cell with after the conference. I also ordered some lead foil so that we don’t have to pound out our own. The sapphire should be fine as long as Sr doesn’t condense on it when it is above 600 C. Otherwise Sr that does find it we can blow off with temperature. I left the cell for the week with the valve at 400 C to blow Sr off of it before we vent and put on new windows. Unfortunately, the sapphire has a lower transmittance than glass (~80% at our wavelength).

There is also the idea that we could lock using vapor in the MOT. But since we don’t know that anybody does that we wonder what problems lie therein.

Research Update June 8

Kind of mundane work today, or maybe it’s just that I’m only writing to keep up the habit and I just really want to go to bed. Let’s get through the highlights.

I closed the angle valve and the pressure in the ion pump went up a decade and half before coming down. It finally settled at ~1 x 10^-8 T! What the heck. Why the huge pressure bump? Why is one pump just as good as two? Either way I wrapped up and stored the turbo pump. It’s nice to have that off the table and out of the way.

I spent way too long this afternoon trying to get the breadboard back on under the MOT chamber. The trick that finally worked? Wedging the faztek nuts in approximately the right place with little balls of aluminum foil to hold them while I installed the board. Even then I still only got 3 out of 4 screws in. I’ll have to check once more to make sure the board doesn’t need that last one.

Scare with the 461 nm laser system today. It was on… and then it wasn’t. and there was no IR power registering on the ammeter. I quickly turned the system off. Then I noticed that the temperatures on both the TA and the master were off the set point. The TA was at ~11 C and the master at ~22 C. A tweak and both came back. However, this put the master about 2 wavenumbers lower than the transition. I finally got it back close by setting the temperature around 25 C. I’ll have to remember to write that down tomorrow so that I don’t forget. When I was running the system later there was a sudden decrease in power on the TA and the current was suddenly running about .6 A lower than it should have been. Very scary and very frustrating. I don’t know if it’s electrical noise or soft power cycling that seems to be rewriting new values to the DAC, but if it turns off the TA while it’s coupled I’m screwed.

Tried to see absorption in the cell one last time and finally had to cool it and reinstall the cartridge heater. I was just getting an optically dense strontium vapor when I had to shut down for the day. Here’s crossing my fingers for tomorrow.

Research Update June 7

This morning the ion gauge read ~8.3x10^-8 T which seemed like a really good sign. Anyways, I started up the ion pump with the chamber cold on the gamble that I wouldn’t have to heat the whole thing up again. The burp took the pressure up to 10^-4 T and then eventually settled at 1x10^-8 T on the pump and 1.28x10^-7 T with the gate valve open again. I rattled around pretty good on the back of the pump after I started it.

I’m not sure why the discrepancy between the pump and the gauge. For the life of the chamber the pump has always read about a factor of 2 below the ion gauge. I don’t know why it’s a whole decade now. I decided that this was good enough though and that I didn’t need to heat up the whole chamber again.

I spent the better part of the day restoring the MOT chamber to it’s operational status and a significant part of the day trying to take a picture of the stupid doubling cavity. I was trying to use dry ice and water to create a vapor that the beams could diffract off of, however, the filters in the camera are really high quality and there is almost zero sensitivity to IR photons. The best I could do was get a picture showing the blue beams.

When I was on the oven for the chamber I tightened the bolts on the nozzle flange up to torque (they were loose too). I needed to get the bronze slug around the oven off in order to install the slowing coils. However, one of the bolts on the thing had frozen and I had to drill it out. Very frustrating. After I put the coils on I installed the oven slug held together solely by the oven heater. I also matched the nozzle and back heaters so that they heat together in parallel and not unevenly.

I wanted to get a high quality picture of fluorescence in the MOT, but the laser was being a real pain the but tonight. I spent the time while things were heating up to clean some of the lab and then align the beam, but by the time things were hot the laser was not cooperating. I think I’m going to have to reoptimize the wavelength. It seems to have drifted and now wants to lase quite a bit up in wave number. blah.

I also think I shot myself in the foot with the picture, because I had aligned the slower beam straight down the nozzle. I could see light fluorescing off the side of one of the windows but I could never see a beam in the center of the chamber with 3 laser beams intersecting through it.  I’ve been thinking about it and I think the slower beam was blasting the atoms back into the oven  on resonance and I was watching the reflection off the front of the oven flash on and off with the atoms. When it was on resonance there were no atoms left to fluoresce off the other beams. I can check that out tomorrow.

Research Update June 6, 2011

Not much to report today. Dallin suggested that I wasn’t seeing much absorption through the cell because I was completely saturating the transition. However, I put about 3.3 ND in the beam and it still didn’t look any different. The laser has drifted some and now wants to lase at the transition when the current is somewhere between 116-118 mA.

The MOT cooled down over the day today and the pressure dropped down into the 10^-7s and we’ll see where it finally settles tomorrow. I’m worried about vacuum leaks on the slower window, oven back, and the viton sealed window just to the left of the slower.

Tried to take some awesome pictures today… they weren’t so awesome. .

Research Update June 3

The day was spent bringing the MOT up to bakeout temps and doing some writing. It’s kind of boring stuff to detail here and the important stuff is in my lab notebook. I will mention that as soon as I started heating up the slower window the pressure was really sensitive from the get go to it. So I unwrapped it and found that the flange bolts were not up to torque anymore after the first temperature cycling. I was a little rattled by that. I tightened them again, only one had stayed at torque. It looked that did it and I’m really counting on it since I don’t want to have to bake one more time.

Research Update June 2

Kind of a frustrating day today. I finished alignment of the 461 nm beam throughout the entire lock setup. I always forget how long alignment can take the first time it’s done. That took me the first part of the day. While I was doing that I brought the slower window up to 375 C, the nozzle and back up to 360 C, and the oven up to 250 C.

The pressure in the MOT peaked at ~2x10^-5 T and started coming back down. It only came down to about 2x10^-6 T which I thought was pretty good but not good enough as will soon be seen.

After the aligning the laser, I put the saturated absorption signal on a photodiode to look at on the o-scope. However, there was so much noise on the laser that it was impossible to see any sort of absorption signal happening. While I was doing the laser alignment I played with the rf power for the lock a little bit. I took a 2 dBm attenuator from the amplifier input and put it on the Vmod output of the box that goes to the phase detector. This made the signal going to the AOM at 6.9 V rms and just under 1 watt (1 watt is 7.07 V rms), and the input to the mixer is now 544 mV rms and just under 8 dBm where the mixer is spec’d at 7 dBm and has a damage threshold of 15 dBm.

I looked more closely at the laser and could see that the beam was visibly bouncing around a little bit. It was also easy to see this on the farthest beam point in the MOT alignment. I tracked it back to the doubling cavity box. I’m pretty impressed with my lock circuit that it could keep the laser locked at all with that kind of mechanical noise affecting the cavity. However, it’s not going to fly for running the experiment.

I think the problem is the pump on the MOT chamber at the moment. I put my hand on the top of the doubling cavity box and the throbbing of the pump was noticeably moving the whole enclosure. I’m pretty sure the piezo mounted mirror is shaking up and down with all the vibration.

Still, I noticed that with the mot at the temperatures above and the laser scanning across the resonance there was strontium fluorescence in the mot chamber. This was exciting for at least one reason: we don’t have to worry about evaporating another thin oxide layer off the strontium. However, because of the temperatures it probably means that when we did evaporate the oxide we managed to turn out nozzle into a source itself, which is bad because it has direct line of sight to the new mirror I just put in.

This is also a bad sign in terms of the vapor cell because if I could see fluorescence with those modest temperatures on the MOT, why then is it barely noticeable in the vapor cell? Argh. So I think that maybe there is a major cold point at the valve. The valve comes right out across the flange top into the air and by the time it gets to the knob its cold enough to touch for opening and closing when the band heater is at 400 C. I’m going to slip a thermocouple in there to see what the temperature is when the valve is hot. Hopefully, we don’t have to put the cartridge heater back in the cell now that I’ve got it in the setup. I put the valve up to 380 C at the heater and still there was no significant change in the absorption. I’m really confused by this, maybe we have to run it with the valve cold and the cup really hot.

Anyways, until I can turn off the pump on the MOT I’m stymied on the laser system. When I cooled down everything but the ion pump the pressure only came down to 1x10^-6 T. Very depressing. I’m going to have to bake out the MOT chamber entire again. I started preparing the chamber to heat but couldn’t get it done to bake out over night. I did manage to get all the heaters installed but couldn’t get the setup insulated or wired. Instead of trying to force the plate heaters on the top and bottom of the chamber again where they don’t really sit right and can unevenly heat the viton sealed windows. Instead I machined plates that could fit over the top and bottom window ports. I then used the double sided high temperature tape to coil heat tapes on the top and bottom of the chamber main body. The aluminum should help prevent hot spots from occuring and burning out the tape.

First thing tomorrow is insulate and get the chamber under heat. It’ll probably take way too long to get all that down.  I can also go ahead and align and tune the ionization laser and maybe even the ion fluorescence laser. I had better figure out if I’m going to want the cartridge heater on the vapor cell before I do that last though.

Research Update May 31–June 1

Things are moving along fast now. I spend the better part of yesterday working on the vapor cell while the MOT pumped down with the ion gauge hot at ~280 C. I removed the cartridge heater from the vapor cell and insulated the bottom as well as the valve. Now when the windows are heated to 380 C the valve comes to equilibrium at 217 C and the cup comes up to 304 C. I brought the valve up to 350 C which then raised the cup to 322 C. This should have resulted in a vapor dense enough to absorb almost all the light, but I could only notice the absorption by eye when looking at the edges of the beam profile. However, I did not have the opportunity to during the day to setup up a photodiode and find out what was really going on. Any noticeable absorption by eye should be enough to provide a signal to lock to however. I started lining up the lock but found that the cell was sitting slightly slanted and that the beam height on one side of the cell had to be lower than the fixed height of the pedestals allowed. I was worried about damage to the AOM, but found that it with our beam diameter of ~ 2mm going through a 200 mm lens it would take 7 mW of light to meet the damage threshold. Since at best we send 8 mW to the lock and then we split that for the saturated absorption setup, there should not be any need to worry.

Today I spend almost the entire day on the MOT, which was kind of slow since I was pretty much just babysitting it like a nervous wreck sure that something would go wrong. I turned off the ion gauge everytime the pressure hit 1X10^-4 T. This happened when I brought the oven above 150 C, and again when I brought the heaters up to 400 C. During the entire day I kept a dry ice pack on the blank facing the oven and the temperature at the blank never rose above –10 C and sat mostly at ~-20 to –40 C.

After baking for an hour at 400 C the pressure had come down to ~ 2.7x10^-5 T. I decided then to bring the oven up to ~ 700 and evaporate the oxide layer on the strontium. Unfortunately, I’m an idiot. When I bought the new heater for the oven the one that was in stock was a 240 V 400 W heater. I so I made the stupid mistake of thinking it would be 200 W at 120 V. So stupid, a factor of 2 in voltage is a factor of 4 in power. This actually works really well for normal operation because if that controller gets the switch stuck again it means that the temperature won’t run away like crazy. But for evaporating the oxide layer this is a problem. Anyway, I borrowed a 2-1 transformer from Scott Daniels and wired it to a variac so I would have some control over the heater. That did the trick. At about 670 C the pressure hit 10^-4 T and I turned off the ion gauge. The foreline pressure actually rose to about 3.6 mT before starting to come back down. I was going to wait until the forline pressure came all the back down to .4 mT but I turned the laser on for Mark and it just happened to lock on the transition. The MOT chamber BURST into light with the laser. After the laser hopped I started it scanning.

There was obviously A LOT of Sr floating around the chamber so I turned off the oven and cooled everything down. To keep the blank cold while I was at Ben’s baseball game I put a cardboard box around the flange filled with dry ice. I wasn’t sure how long it would last because the sits right next to the ion gauge which is effectively a heat source, but it stayed cold until I was prepared to vent the chamber.

There was one unintended consequence. The window just to the left of the blank has a direct line of site from the nozzle and was clouded by strontium during the run. Luckily, we had one extra window and I swapped it out while the chamber was vented. The window to the right did fine because it sits on a longer arm and doesn’t have line of site.

I can’t understand what happens, but just like with the vapor cell the black oxide gunk we burned off, of which there should have been a ton, disappeared when I vented the chamber with argon. I can’t figure out what happens to it. Before I vented the chamber the pressure had come down to 2x10^-7 T again which is a good sign. After putting the slower window back on and changing out the clouded window I started pumping down again. I don’t like the duniway gaskets because they down allow the the flanges to press as close together as it feels like they should when the bolts are to torque. Nevertheless, the seal must have been good because the pressure came right down into the 10^-6 T range. I turned the heater on the pump back on and we’ll see what things look like in the morning.

I didn’t heat the vapor cell today but just worked on the beam alignment. While I was working on the MOT Mark tried to straighten out the vapor cell tilt. He did okay, it still lilts to the one side but its workable. Anyway, I was able to align the laser to the AOM and finish out the saturated absorption alignment. Tomorrow if things go very well we’ll see exactly what kind of signal we get without a cartridge heater and maybe even finish out the lock. If things go EXTREMELY well we might even make our first ions, although I doubt I’ll get the MOT alignment and the lock done with enough time left to do that.

Diet Update

Sorry for the silence. It was more enjoyable for me to not blog during my vacation than to continue tracking my weight. I don’t have time to really write about my lifestyle for the next couple of weeks and I did the month of the diet that I planned to do. In all I lost 10 lbs and more than 2 inches off my waistline. It was only half of the promised weight loss but I only read the 3 most basic chapters on the diet before starting and I didn’t bother to consult the book anymore after that. So all in all I think it went pretty well. I don’t have the time to be worrying about what I eat for the next little while, but I plan on keeping to pretty much the same regimen except I’ll add in fruits, berries, cheese, and I won’t sweet the occasional carb. If you want to know what I’m thinking about instead you can follow the research updates. And I apologize in advance for not writing the research updates in  a more intelligible way .