Noise projections for geo 600
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Noise Projections for GEO 600. Joshua Smith GEO Meeting 11.10.06. Detector output decomposed. transfer function. detector output. noise source. detector output:. noise channels:. Noise channels. noise channel. transfer function. detector output. noise source. detector output:.

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Noise Projections for GEO 600

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Noise Projections for GEO600

Joshua Smith GEO Meeting 11.10.06


Detector output decomposed

transfer function

detector output

noise source

detector output:


noise channels:

Noise channels

noise channel

transfer function

detector output

noise source

detector output:


noise channels:

Noise projections

noise channel

transfer function

detector output

noise source

detector output:

noise projections:

noise budget:


Simplified procedure I

Causality key

  • Notes:

  • Causality key

  • Simultaneous DFTs allow comparison

  • Other variants exist, eg open-loop which requires CLTF


Simplified procedure II

Causality key

Normal operation


Simplified procedure III

Causality key

Normal operation


Latest noise budget for S5


Noise projection: alignment FB

 feedback

noise projection

transfer function


Noise projection: (de)modulation phase I

P

Q

H


Noise projection: (de)modulation phase II


S5 NP Reconstruction

Goal: Noise projections (full budget) at any time.

Coming soon: ProjMon

  • Transfer functions:

    • Measure accurately about once per month

    • Track using calibration lines

  • 2. Fourier transforms of Nj and H:

    • Signals recorded continuously anyway…


Calibration lines


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


Vetoes of false gravitational waves

  • Noise channels contain almost no GW info

  • Coincident (within windows) events are not GWs !

  • See Ajith and Martin’s talks !

Example: injected burst-like waveform


Noise subtraction: alignment FB

Error at a given freq. vs. filter accuracy

H

H’

Results of a time-domain subtraction


The End


Noise removal, eg., frequency noise

Most important role of NPs in commissioning: Identify limiting noise sources – team removes them


Noise projection: laser frequency noise

 Transfer function calculation would require very sophisticated model

Noise projections well-suited for very complicated systems


Limitations: loop gain

Single-path loop

Simulated results

Workarounds exist:

eg., for high loop gain


Limitations II

Single-path loop

Split-path loop

Workarounds exist: eg., for high loop gain


H’ vs signal recycling FB


Detector output I

transfer function

detector output

noise source

detector output:


Detector output II

transfer function

detector output

noise source

detector output:


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