[Kiwamu Izumi,Sheila Dwyer,Vaishali Adya]
Objective : Reproduce the measurements from 34389 with 'the' correct power normalization, investigate the most dominant beam jitter coupling mechanism into DARM
Method : We tried to move the PR3 spot position by moving the PRM in pitch and yaw and measured the coherence from the four channels of the BullsEye photodiode namely PIT,YAW,Beam Size and Sum into DARM. The channels have now been named in accordance to what we expect to see ie. PIT=pitch, YAW=yaw, WID=beam size,SUM=sum.
We tried to go to configuration (B) where POP_A_PIT = -0.4, POP_A_YAW = +0.3, PRG = 32.5. Upon doing that we also tried a new Configuration (D) where POP_A_PIT = -0.03(original position before misaligning the spot), POP_A_YAW = +0.3, PRG = 29.
Results :
Key to the plots 1 and 3 : Blue =Low Noise, Green =configuration B, Red =configuration D
Plot 2 is just the coherences using IOP channels to monitor the high frequency parts(aka 4 kHz noise hunting)
plot 4 is the coherence between the BullsEye degrees of freedom
- The broadband noise and the slight elevation in noise between 200 Hz-1kHz was reproduced (see plot 3) with the peculiarity that pitch showed a distinct elevation (of about a factor of five) in comparison to the measurements from 34389 (see plot 1)
- The coherence plots taken today seem to agree with the hypothesis that the broadband lump might indeed be from some form of beam jitter.
- Upon going to configuration D we did notice that the coherence of PIT decreased only marginally from 0.6(green) to 0.5(blue)
- Pitch signals didn't show high coherence with the SUM signal (see plot 4)
Next steps :
- Calibration of the signals and calculation of the coupling coefficients
- Check whether this noise coupling entirely explains the excess noise in DARM
