we did some measurements and the signal gone again. on the same time, we use our phone camera try to take a closer look on the crystal. and find out  the coil wasn’t cover the crystal.

the reason is, the “neck” of the coil, which is the part connect the coil to the cable is shrunk. should be due to a fiction of the coil and the sample tube and that pushed the coil. we think the coil cannot be shrunk any more. thus re-position the coil and the signal come back.

the signals measured today has long period.

since the coil was re-position, we have to measure everything and time run out. we planned to do it tmr.

and i fixed the setting and add a half-waveplate for laser polarization measurement. it seem that there are something, i took 4 data for every angle. however, when i finished a cycle and re-measure again, the signal is not quite the same.

by the way, we have no idea the crystal orientation, the laser polarization can have a complicated effect on the crystal since it has all 3 projections on the principle optical axes.

Thus, i think the laser polarization measurement is too early.

a proper optimization procedure should be:

  1. microwave delay time
  2. microwave power
  3. laser duty
  4. laser power
  5. crystal orientation
  6. laser polarization
in order to compare different set of data, instead of same data set. we really have to fix and make sure the NMR coil give same impedance and the NMR system give same power output.
the impedance of the coil can be identified by the coil relaxation signal. and the NMR power output should be recorded by CRO.
  1. continuous the laser duty
  2. find a way to fix the coil impedance and NMR output power
  3. crystal orientation and laser spot size and location
  4. laser polarization
  5. Data analysis ( report )