Identifying limiting noise sources of GEO600

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Identifying limiting noise sources of GEO600

• ILIAS WG1 Meeting
• Joshua Smith for the GEO team

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Sensitivity Progress
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June 04 vs. Theoretical
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Noise Projections

• Idea
• consider example measurement points (chans), N
  and P
• determine how noise in N will appear in P based
  on properties of system
• Procedure
• 0 Identify noise that could couple to P
• 1 Find/create channel (N) that represents this
  noise
• 2 Quantify coupling from this channel to P with
  a TF
• 3 Quantify noise in N and P by their ASDs
• 4 Project the noise in N to how it will appear
  in P
• Drawbacks
• assumes linearity
• not reliable at frequencies with loop gain.

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Transfer Function

• Dominate noise present in system with injected
  signal
• Measure TF

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Projection

• Remove signal
• Measure ASDs simultaneously at N and P
• Multiply by TF to form projection

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MI loop (MI diff. arm-length)

• LSC_MID_EP-P_HP
• main GW signal, P quadrature
• LSC_MID_FP-MCE-MCN
• ? diff. FB to ESDs (gt 15 Hz)
• LSC_MID_FP-MCE-HV, LSC_MID_FP-MCN-HV
• ? feedback to MCe, MCn ESDs sampled after HVA

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MI Fast Path
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MI Fast Path TFs
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MI Fast Path ASDs
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MI Fast Path Projections
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Current Noise Projections
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Oscillator noises
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Some other noises

• MI oscillator noises
• amplitude2-3 below from 400Hz to 1.1kHz (at
  least)!
• Phase 8 below _at_ 1kHz
• acoustic noise
• Couples at some level, output bench and TCMb-West
  breadboard strongest
• MIC VIS a hot spot for acoustic coupling
• scattered light
• visible problem, nonlinear, excited with e.g.
  stomps
• frequency noise
• complex PR loop difficult to characterize,
  requires more work
• gain reduction of 100 just increases noise in P
• apparent arm length difference for freq coupling
  is about 2.8m

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In the works

• Acoustic/air fluctuations, scattering
• output optics, HPD in vacuum
• Acoustic shield for TCMb-West, other places?
• MI fast path noise
• switch out sqrt-circuit electronics finished,
  installation imminent
• MI oscillator noises
• phase new generator or 2f
• amplitude stabilization loop
• dark, shot noises
• Increase laser power new HPD
• Front end-limited loops (SRC, MI slow, etc.)
• noise may reduce with reduction of noise in other
  loops
• Cross-projections MI to SRC, etc.

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The End
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Future of projections?

• Things to address for projections
• use phase information for split paths, etc
• produce reliable information in loops with high
  loop gain
• Automation
• track TFs using callines
• monitor veto channels during data runs
• Overall Goal
• speed progress towards design sensitivity