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Measuring Gravitational Waves with GEO600

Measuring Gravitational Waves with GEO600. Martin Hewitson, AEI Hannover for GEO600. GEO600 optical layout. MC2. MPR. MC1. MFn. MCn. BS. MSR. MCe. MFe. Overview. h(t). GEO. v(t) [V]. Noise e.g., seismic, laser. calibrate. 1 GEO. v(t) [V]. h(t) + noise. Q(t) [V]. P(t) [V].

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Measuring Gravitational Waves with GEO600

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  1. Measuring Gravitational Waves with GEO600 Martin Hewitson, AEI Hannover for GEO600

  2. GEO600 optical layout MC2 MPR MC1 MFn MCn BS MSR MCe MFe DPG, March 2005

  3. Overview h(t) GEO v(t) [V] Noise e.g., seismic, laser calibrate 1 GEO v(t) [V] h(t) + noise DPG, March 2005

  4. Q(t) [V] P(t) [V] filter Inside the GEO box h(t) detected h(t) Optical cavity + v(t) [V] Seismic noise Keep detector at its operating point (dark fringe) DPG, March 2005

  5. Calibration of GEO600 • Time-domain calibration method • Optimisation routine is used to quasi-continuously estimate parameters of optical response • Update rate is 1Hz DPG, March 2005

  6. Calibration procedure Michelson servo model • Correct for MI loop and Optical transfer function(s) x = Calibration functions Optical transfer functions DPG, March 2005

  7. optical On-line optical TF measurements CAL P and Q actuator DPG, March 2005

  8. calibration Calibration overview DPG, March 2005

  9. Combining hP(t) and hQ(t) - I • Idea is that • So we can form • Do this in the time-domain to fit in with the current calibration method hP(t) = h(t) + nP(t) hQ(t) = h(t) + nQ(t) hopt(t) = a(t,f).hP(t)+b(t,f).hQ(t) DPG, March 2005

  10. Combining hP(t) and hQ(t) – II • Form optimal frequency dependent weighting of hP(t) and hQ(t) by considering variance of noise components Convert to time-domain filters DPG, March 2005

  11. Combining hP(t) and hQ(t) – III • Simplification: consider only magnitude • Create filters from noise floor estimates sQQ sPP sPQ h(t) = Pfilter{hP(t)} + Qfilter{hQ(t)} DPG, March 2005

  12. Combining hP(t) and hQ(t) – results Get the best of hP and hQ plus a little extra! DPG, March 2005

  13. Summary and future work • Online time-domain calibration of GEO600 output(s) to strain sensitivity • Both output demodulated output quadratures are calibrated and combined to give (almost) optimal h(t) • Extend this to allow for time variation of combining filters and to include non-linear phase correlations in the output quadratures DPG, March 2005

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