Noise Projections for GEO 600

Joshua Smith GEO Meeting

11.10.06

Detector output decomposed

detector output:

detector output

noise source

transfer function

Noise channels

noise channel

detector output:

detector output

noise source

transfer function

noise channels:

Noise projections

noise channel

detector output:

detector output

noise source

transfer function

noise projections:

noise channels:

noise budget:

Simplified procedure I

Causality key

Notes:

1. Causality key

2. Simultaneous DFTs allow comparison

3. 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

transfer function

feedback

noise projection

Noise projection: (de)modulation phase I

P

Q H

Noise projection: (de)modulation phase II

S5 NP ReconstructionGoal: Noise projections (full budget) at any time.

Coming soon: ProjMon

1. 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

Results of a time-domain subtraction

Error at a given freq. vs. filter accuracy

H’

H

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

Noise projections well-suited for very complicated systems

Transfer function calculation would require very sophisticated model

Limitations: loop gain

Single-path loop

Workarounds exist:

eg., for high loop gain

Simulated results

Limitations IISingle-path loop

Split-path loop

Workarounds exist: eg., for high loop gain

H’ vs signal recycling FB

Detector output I

detector output:

detector output

noise source

transfer function

Detector output II

detector output:

detector output

noise source

transfer function