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Reports until 17:48, Friday 18 November 2016
H1 ISC
daniel.sigg@LIGO.ORG - posted 17:48, Friday 18 November 2016 (31631)
Jitter Measurements (Again)

The DBB shutter was opened to allow for more jitter measurements. The measurements are:

  1. File B: In lock for a long time (>24h), we see jitter coherence with DARM around 500 Hz as high as 0.35.
  2. File A: Moving to an alignment with higher power recycling gain (32 instead of 30.5) increased the coherence as high as 0.5.
  3. File C: At the beginning of the next lock the coherence was around 0.15.
  4. File D: Moving to the alignment with higher recycling gain increased this coherence to 0.35.

There is clear correlation where the alignment with higher recycling gain has a higher jitter coupling. There also seems to be some thermal effect where the interferometer initially has a lower coupling.

The calibration of the DBB QPD jitter is just the inverse of the sum divided by 60 to account for the PMC transmission. The jitter measured by the IMC WFS DC was scaled by 1/3 to match the measurement when the IMC was unlocked.

Looking at the comparison of jitter during O1 and now (alog 30581) as measured by the IMC WFS DC, one might expect that the HPO jitter can explain all excess low frequency jitter below 70 Hz. This seems to work fine for pitch, but not very well for yaw. The coherence between WFS B DC yaw with the DBB QPD channels isn't higher than 0.3.

The effect of the alignment change on the DARM jitter coupling makes one wonder, if there isn't a Gouy phase conspiracy, where the coupling of the periscope peak is mostly independent. The Gouy phase difference between the periscope peak and the HPO jitter seems to be roughly 120°, if we believe the WFS DC readbacks. MC_F and REFL_SERVO_CTRL mainly see jitter peaks after the PMC. The auxiliary length dofs don't see much more than the periscope peak itself. Only DARM seems to be sensitive to the HPO jitter.

Non-image files attached to this report
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