Flaminio Photodiode noise

Photodiode noiseduring the E4 and E3 runs: 

Photodiode noise during the E4 and E3 runs Raffaele Flaminio

Noise measurement I: 

Noise measurement I All shutters closed on Friday evening during 10 minutes GPS time [710540650 – 710541290] More data available on Saturday nigh while IMC out of lock noise rms ~ 2 mV

Noise measurement II: 

Noise measurement II noise spectrum shape: anti-compression filter

Photodiode noise vs ITF noise: 

Photodiode noise vs ITF noise Beam B1

Photodiode noise vs ITF noise: 

Beam B1’ Photodiode noise vs ITF noise

Photodiode B1 vs Photodiode B1’ : 

Photodiode B1 vs Photodiode B1’ Blue = Beam B1’ Red = Beam B1

B1 vs B1’: closed loop spectra: 

B1 vs B1’: closed loop spectra Beam B1 Beam B1’

B1’ vs linear alignment signals: 

B1’ vs linear alignment signals Beam B1 Beam B1’ Linear alignment error signals qx error signal qy error signal

B1’ ~ linear alignment signals: 

B1’ ~ linear alignment signals Blue = Beam B1’ Green = combination of linear alignment signals

Photodiode noise during E3: 

Photodiode noise during E3 Similar but opposite situation: B1 > B1’ at low frequency

E3: B1 ~ linear alignment signals: 

E3: B1 ~ linear alignment signals Red = Beam B1 Green = combination of linear alignment signals

A possible model: 

A possible model B1  dL + a  dq sensitivity to angular motion (probably due to mode-cleaner) B1’  dL only sensitive to longitudinal motion (except for mechanical coupling) When loop closed using B1, closed loop signals are: B1  (dL + a  dq) / (1+G) B1’  dL/(1+G) – a  dq  G/(1+G) G = open loop gain When loop closed using B1’, closed loop signals are: B1  dL/(1+G) + a  dq B1’  dL/(1+G) G = open loop gain According to E3 and E4 data a ~ 5  10-4 m/rad (measured at the 3.5 Hz qx resonance)

Photodiode B1 vs Photodiode B1’ : 

Photodiode B1 vs Photodiode B1’ Blue = Beam B1’ Red = Beam B1

OMC temperature scan : 

OMC temperature scan temperature OMC transmission c2  TEM00 Interferometer locked to B1’

OMC temperature scan : 

OMC temperature scan temperature OMC transmission c2  TEM00 Dark fringe signal B1 signal depends on the mode resonating in OMC B1 signal  0 even when OMC locked to TEM00 Different dark fringe conditions on B1 and B1’ Interferometer locked to B1’

Photodiode B1 vs Photodiode B1’ : 

Photodiode B1 vs Photodiode B1’ Blue = Beam B1’ Red = Beam B1 Difference at higher frequencies: 200-600 Hz Photodiode B1’ not locked on dark fringe offset ~ few ·10-10 m Coupling of power fluctuations: dP/P ~ few · 10-5 Hz-1/2 dl = offset  dP/P ~ 10-14 m/Hz-1/2

Conclusion: 

Conclusion B1 electronics noise never limit the ITF sensitivity during E3 and E4 Differences between B1 and the B1’ spectra appear both in the E3 and E4 data E3: B1 > B1’ E4: B1’ > B1 Difference at low frequency: larger sensitivity to angles of the out-of-loop photodiode probably due to a greater B1 sensitivity to angular motions probably due to the OMC could become a problem if dq too large Difference at high frequency larger sensitivity to power fluctuations of the out-of-loop photodiode due to the offset from the dark fringe of the out-of-loop photodiode no problem