Here are the results from the fit. Data can be found on nodus in /users/aaron/40m/data/PMC/190617/. I've put a jupyter notebook with the analysis in /users/aaron/40m/analysis/PDH_calibrate.ipynb (might be some filename issues due to different directory structure on my laptop).

Here's a summary of the current measurement. I'll be referencing the diagram for the PMC servo card.

1. With the PMC servo loop open, sweep the PMC PZT by sending a triangle wave in to J5 (external drive on the servo card).
   1. I used a 100Hz drive, but should use something slower so my drive isn't filtered out by the 100Hz pole on the servo card and the 10Hz pole on the PZT.
2. Monitor the voltage at the HV drive, as well as at "mixer out" (J8 on the servo board)
   1. Note that I took this PDH error signal from FP2TEST rather than "mixer out", which means my error signal was not low pass filtered.
3. Calibrate the HV mon in units of Hz by fitting the PDH signal. The sidebands should be 35.5Mhz away from the carrier peak.
   1. This part needs to be done differently to account for thermal locking in the PMC.
4. You now have the PDH error signal as a function of PMC resonance in Hz, and can use that to calibrate the PDH error spectrum.
   1. The spectrum is taken when the PMC is locked, so the Hz/V scaling is the slope of the PDH error signal.

In the figures below, I obesrved that for fast (100Hz) drives, the PDH error signal had a pi/2 phase shift relative to the triangle wave, which means even though the resonance appears near the turnaround of the triangle, it is actually occuring near the center of the range.

There are several problems with this data:

• PMC error signal spectrum is not properly calibrated, even according to the process described above
• The drive was faster than the response of the PZT.
• I was driving with a ~1V excitation, so I've lost a factor of 10 somewhere on the way to the external drive curve. Probably just a problem with how I've read the data dump from the scope.