Post on 02-Jan-2016
transcript
Gabriele Vajente
ILIAS WG1 meeting - Perugia 20.09.05
Couplings of angular Couplings of angular noises into dark fringenoises into dark fringeDiffused light studiesDiffused light studies
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 2
SummarySummary
• Non-stationary noise couplings due to input beam jitter
• Preliminary study of daily trends
• Preliminary projections of angular control noise
• Acoustic noise by diffused light
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 4
Input beam jitterInput beam jitter
• Temperature fluctuations in Laser Lab causing input beam jitter
• Powers oscillates with 20 min period• Does this input beam jitter couple into high frequency noise?• Search for modulated noises analyzing long locks (up to 40 h)
IMC transmission and PRC pick-off powers IMC end quadrants diodes
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 5
Input beam jitterInput beam jitter
• Temperature fluctuations in Laser Lab causing input beam jitter
• Powers oscillates with 20 min period• Does this input beam jitter couple into high frequency noise?• Search for modulated noises analyzing long locks (up to 40 h)
IMC transmission and PRC pick-off powers IMC end quadrants diodes
0.7 mHz
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 6
Analyzed configurationsAnalyzed configurations
• During C6 run:– “bump” between
100 – 300 Hz (diffused light)
– removed before the end of the run
• During M9 minirun:– New power
stabilization scheme
Input laser power is stabilized using a pick-off before the IMC
Input laser power is stabilized using the power transmitted through the IMC
Dark fringe spectrum with and without the “bump”
The “bump” was acoustic noise re-injected by diffused light at north end bench
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 7
Analysis methodologyAnalysis methodology
• Computed DF spectrum at intervals(every 5s or 20s, 60s window length, 216 points for each FFT)
• Computed band-limited RMS: [0, 2], [2, 10], [10, 30], [30, 50], [50, 200], [200, 600], [600, 1000], [1000, 10000] Hz
• Time evolution and frequency analysis of these RMS
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C6 lock C6 lock (without bump)(without bump)
Spectrum of dark fringe band-limited RMS time evolution
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 9
C6 lock C6 lock (without bump)(without bump)
Spectrum of dark fringe band-limited RMS time evolution
2 – 30 HzAngular noise? Coherence with BS, NE, WE and ISYS angular corrections
0.6 – 1 kHzAcoustic noise from the ISYS?
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 10
C6 lock C6 lock (with bump)(with bump)
Spectrum of dark fringe band-limited RMS time evolution
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C6 lock C6 lock (with bump)(with bump)
The “bump” is modulated at 0.38 mHz.
Correlated with NE building temperature
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 12
New power stabilization schemeNew power stabilization scheme
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 13
New power stabilization schemeNew power stabilization scheme
No more modulated noise!
Conclusion:
All these noises were acoustic/angular noises of ISYS coupled through the power fluctuations in the IMC.
IMC tx IMC ty
IMC trans. RFC trans.
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 15
Daily trendsDaily trends
• During one weekend ITF locked continuously for more than 28 h with all 10 LA loops closed
• Clear daily trend in dark fringe power• Seems to be stable between different locks
Dark fringe after OMC
Dark fringe before OMC
PRC pick-off power
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 16
Effect on dark fringeEffect on dark fringe
Dark fringe demodulated signal
Dark fringe DC signal
Red: DF DC maximum
Green: DF DC minimum
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CoherencesCoherences
B7 DC B7 ACp B7 ACq
B8 DC B8 ACp B8 ACq
Control noise?
Diffused lightRed: B1 DC maximum, Green: B1 DC minimumB7 = NE transmitted beam B8 = WE transmitted beam
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 18
Projections of angular Projections of angular noisesnoises
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Projections of angular noisesProjections of angular noises
• Strong coherence of all angular corrections with dark fringe
• Can compute approximate transfer functions to DF without noise injections
• All angular error signal are coherent with each other
• Can “project” angular noise into DF
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Projections of angular noisesProjections of angular noises
• Strong coherence of all angular corrections with dark fringe
• Can compute approximate transfer functions to DF without noise injections
• All angular error signal are coherent with each other
• Can “project” angular noise into DF
THIS MAKES SENSE ONLY FOR THE DOMINANT SIGNAL!
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 21
Projections of angular noisesProjections of angular noises
Dominant noise source is WI (under local control!)
It’s possible to strongly reduce its gain (by a factor of 20)
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 22
Projections of angular noisesProjections of angular noises
These projections are automatically computed via an octave program
Needed independent measurements of transfer functions!
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 23
Diffused light Diffused light investigationsinvestigations
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Diffused light investigationsDiffused light investigations
• First step: 100 – 300 Hz bump coherent with north end signals
• Found several stray beams in north end bench
• The strongest one comes from the flip mount used to attenuate the beam in front of the quadrants
NE beam
QuadrantsDark fringe spectrum
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Diffused light investigationsDiffused light investigations
• The beam hit the bench box and was diffused• When the box was open, the bump disappeared• Installed a cylindrical-conical aluminum beam dump
• Gain in sensitivity and NS-NS horizon stability
• The same beam in WE bench was dumped with black foam
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 26
Diffused light investigationsDiffused light investigations
• Second step: 100 – 300 Hz coherence with WE signals
h_rec [1sqrt(Hz)]h_rec [1/sqrt(Hz)]
Straylight bump
• Black foam was not sufficient for this beam dumping
• Beam hit the box not orthogonally
• Used black AR-coated glass
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 28
ConclusionsConclusions
• Input beam jitter couples with angular/acoustic noise– disappeared using new laser power stabilization scheme
• Daily trends (still input beam jitter)– will be solved with ISYS drift control
• Stray light has a major effect!– Need to careful dump every stray beam…
• Angular control noise – Dominant with Local Controls– AA not yet optimized. Noise re-injected up to some tens of Hz
ILIAS WG1 meeting 20.09.05 – Gabriele Vajente 30
VIRGO simplified optical schemeVIRGO simplified optical scheme