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Reducing the Noise in GEO600

Reducing the Noise in GEO600. Joshua Smith for the GEO 600 team. Noise Projections: hP. Noise Projections: hQ. Non-stationary Noise. At best the noise is very close to the Projections. Shot + Dark Noise. MI Detection Noises: P. MI Detection Noises: Q. Optimal h(t)  Shot Noise.

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Reducing the Noise in GEO600

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  1. Reducing the Noise in GEO600 Joshua Smith for the GEO600 team Perugia, Italy 20.09.05

  2. Noise Projections: hP Joshua Smith, Perugia, Italy 20.09.05

  3. Noise Projections: hQ Joshua Smith, Perugia, Italy 20.09.05

  4. Non-stationary Noise At best the noise is very close to the Projections Joshua Smith, Perugia, Italy 20.09.05

  5. Shot + Dark Noise Joshua Smith, Perugia, Italy 20.09.05

  6. MI Detection Noises: P Joshua Smith, Perugia, Italy 20.09.05

  7. MI Detection Noises: Q Joshua Smith, Perugia, Italy 20.09.05

  8. Optimal h(t)  Shot Noise Combination optimized for SNR of h given: hP = h + nP hQ = h + nQ Joshua Smith, Perugia, Italy 20.09.05

  9. Shot Noise: Next steps • Shot model: 5W to MPR, 7kW @ BS • Currently have: 2W to MPR, 1.5-2kW @ BS • Expect to be: sqrt(7/1.5) to sqrt(7/2) = 2.2 to 1.9 above design (just from cavity power) • Are currently about factor 4 from design level • 10s of % from optimizations, reduction of dark noise • rest (perhaps sqrt(2)) not yet understood • Next Week: Replace Laser • Increase input laser power from 5W to 10W • This will give sqrt(2), for the rest perhaps: • Search for losses in power-recycling cavity • Reduce loss in modecleaners? Joshua Smith, Perugia, Italy 20.09.05

  10. Signal Recycling Longitudinal More aggressive filtering to reach design below 100Hz Joshua Smith, Perugia, Italy 20.09.05

  11. Laser Power Noise • Investigate quality of current signal after second modecleaner • Use Input Port as error-signal for power stabilization 2nd/3rd loop Joshua Smith, Perugia, Italy 20.09.05

  12. MI Fast Auto-alignment • Implemented digital fast auto-alignment this week! • Will allow aggressive filtering like that used in the SR loop Joshua Smith, Perugia, Italy 20.09.05

  13. Oscillator Phase Noise • Wenzel specs = -165dBc @ 1kHz • Unable to measure better than 15dB above OPN in current setup • Better RF setup aims to be limited by phase noise from oscillator • Possible reduction of coupling coefficient with increased MI loop gain Joshua Smith, Perugia, Italy 20.09.05

  14. Michelson Diff. Longitudinal • Required factor for fast path by whitening, bias reduction? • Intermediate Mass FB not front-end limited, improve servo, possibly digital steeper low-passing above ~40Hz ? Joshua Smith, Perugia, Italy 20.09.05

  15. Nonlinear Actuator: Up-con Joshua Smith, Perugia, Italy 20.09.05

  16. Nonlinear Actuator: Beats Joshua Smith, Perugia, Italy 20.09.05

  17. Nonlinear Noise vs. Bias 600V Joshua Smith, Perugia, Italy 20.09.05

  18. Nonlinear Noise vs. Bias 60V Joshua Smith, Perugia, Italy 20.09.05

  19. Nonlinear Noise vs Bias V Further decrease in bias not optimal ! Joshua Smith, Perugia, Italy 20.09.05

  20. Summary • Shot Noise (4x above design)  sqrt(2) from power increase, 10-20% from modulation depth, etc. • Something else needed. Decrease finesse of MCs? • Oscillator Phase Noise  Improved RF distribution to ensure –165dBc @ 1kHz limit from oscillator • More MI gain • Michelson  More whitening, noise mitigation slow path • Signal Recycling  Increased digital filtering • Laser Power  Use MIC VIS in-loop • Auto-alignment  Digital servo allows more aggressive noise filtering Joshua Smith, Perugia, Italy 20.09.05

  21. Optical Layout Joshua Smith, Perugia, Italy 20.09.05

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