Noise Projections for GEO 600

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Noise Projections for GEO 600

• Joshua Smith GEO Meeting 11.10.06

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Detector output I
transfer function
detector output
noise source
detector output
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Detector output II
transfer function
detector output
noise source
detector output
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Detector output III
transfer function
detector output
noise source
detector output
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Noise channels
noise channel
transfer function
detector output
noise source
detector output
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Noise projections
noise channel
transfer function
detector output
noise source
detector output
noise projections
noise budget
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Simplified procedure I
Causality key

• Notes
• Causality key
• Simultaneous DFTs allow comparison
• Other variants exist, eg open-loop which requires
  CLTF

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Simplified procedure II
Causality key
Normal operation
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Simplified procedure III
Causality key
Normal operation
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Latest noise budget for S5
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Noise projection alignment FB
? feedback
noise projection
transfer function
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Noise projection (de)modulation phase
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S5 NP Reconstruction
Goal Noise projections (full budget) at any time.

• Transfer functions
• Measure accurately about once per month
• Track using calibration lines
• 2. Fourier transforms of Nj and H
• Signals recorded continuously anyway

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Calibration lines
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Tracking transfer functions

• At calibration line, projection and H should have
  same amplitude, phase.
• Ratio and difference indicate TF accuracy.
• For 10 day test, about 10 10o

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Vetoes of false gravitational waves

• Noise channels contain almost no GW info
• Coincident (within windows) events are not GWs !
• See Ajith and Martins talks !

Example injected burst-like waveform
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Noise subtraction alignment FB
Error at a given freq. vs. filter accuracy
H
H
Results of a time-domain subtraction
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The End
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Noise removal, eg., frequency noise
Most important role of NPs in commissioning
Identify limiting noise sources team removes
them
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Noise projection laser frequency noise
? Transfer function calculation would require
very sophisticated model
Noise projections well-suited for very
complicated systems
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Limitations loop gain
Single-path loop
Simulated results
Workarounds exist eg., for high loop gain
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Limitations II
Single-path loop
Split-path loop
Workarounds exist eg., for high loop gain
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H vs signal recycling FB