Varun, Stefan

We repeated the PRC Gouy phase measurement that was pinoreered by KAGRA in klog 9241 and 9246.
In short, the method consistes for just kicking the PRC mirror out as fast as possible.

We really want to run this method on the SRC, but today only the PRC was available.

When we finally did it right (measurement 2) we scanned acros 19 FSRs. That allowed us to do a very clean spline fit for the velocity.
We find:
PRC one-way Gouy phase: 23.23deg (mean of 19 measurements in 1 sweep).
Standard deviation of data set: 0.17deg
Standard deviation of mean: 0.04deg.
We would not be surprised if there is some systematic error that is slightly bigger. But we would trust the result to about 0.2deg.

Measurement details:

- Measurement 1: We held MICH at its DC control value, but forgot that the LSC trigger cut it off. (Settings: PRCL2 OFFSET: +3e5) (Plot 1)
- Measurement 2: We didn't bother holding MICH, but froze the POP_RF18 output to avoid the LSC triggering to shut off the drive. (Settings: PRCL2 OFFSET: -1e6) (Plot 2,3)
- xml data files and scripts are attached - more details in folder /ligo/home/controls/sballmer/20191015