User name X. Zheng
Log entry time 02:11:14 on June10,2001
Entry number 62726
keyword=Target - last EPR12:18am, tried EPR with longitudinal laser #6.
scanned by hand, found ~14microV signal;
tried AFP, cannot lockin;
adjust everything, did 2 AFP measurement, none of them is acceptable.
Then I decided to take a break. But when I tried to pump up the cell I turned on 2 other lasers shown on the terminal later found these 2 were transverse. So the oven was pumped by 2 lasers for about 2 minutes.
Then, tried to do one more AFP, found the initial state of helium was wrong, see plot. in the second flip I stopped the program to keep it in the higher state.
After this measurement, tried one more lockin to make sure it is still in the right state. But 5 minutes later I found the lockin resonance frequency was only 11.61 MHz, which is very low and I suspected the state is +3 (the wrong one) again.
Then I tried to lockin to resonance and use AFP to flip it back. The first 2 flips were not succesful, then next one I flipped it to -3 state but it jumped to +3 when I disable the RF excitation. Second time I flipped it to -3 then it jumped back to +3 when I switch the RF capacitor. The third time it looks okay, hope it will stay at -3 forever.
One thing need to emphasize is that I did not stop program in the middle during first 2 measurments. So why did heliums go to the wrong state? One thing that has been noticed is that the damaged photodiode gives much higher noise and makes the lockin much more difficult. Suggest no EPR before June11 (maintaince day).
Polarization extracted is: first measurement: 40.78% with error +- 3%
Latest one: 34.9% with error +-0.5%
So I put 35% into start_of_run comments.
Will do NMR around 6am to check if the polarization survives.
FIGURE 1
