Noise Projections for GEO 600 Joshua Smith GEO Meeting

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 QH

Noise projection: (de)modulation phase II

S5 NP Reconstruction Goal: 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 N j 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% 10 o

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 II Single-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