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Detector Characterization of Dual-Recycled GEO600

Detector Characterization of Dual-Recycled GEO600. Joshua Smith for the GEO600 team. Michelson Interferometer with Dual Recycling. Mode Cleaners. Folded arms with optical path length of 2400 m. 2 triangular ring cavities (8 m optical path length each). Laser. Optical layout.

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Detector Characterization of Dual-Recycled GEO600

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  1. Detector Characterization of Dual-Recycled GEO600 Joshua Smith for the GEO600 team

  2. Michelson Interferometer with Dual Recycling Mode Cleaners Folded arms with optical path length of 2400 m 2 triangular ring cavities (8 m optical path length each) Laser Optical layout

  3. Dual Recycling • PR enhances carrier • SR enhances signal carrier MPR Signal sidebands MSR

  4. Summer setbacks • Local control flag broken off • open tanks & rebond • Broken fused silica fiber • open tanks & replace • Turbo pump failures • Some air leaked into tanks and tubes as a result • Air Conditioning Failures • HOT electronics don’t work! • Signal Recycling locks rare

  5. Cause: Long to tilt coupling in monolithic suspensions • Measured coherence: • mirror tilt • with • ground motion • along beam axis • Understood, oversight in assembly Excess mirror tilt • Mirror tilt of ~1rad @ pendulum resonances makes signal recycling lock acquisition very difficult

  6. Reducing mirror tilt (I) • Digital feedforward of ground motion to suspension point

  7. Reducing mirror tilt (II) • Applied digital FF correction for the tilt introduced by longitudinal feedback to intermediate mass

  8. Locking dual-recycled GEO600 • Problems with locking on SR error signal • narrow catching range • SR mirror motion too large • Invented new acquisition scheme • Pre-lock on “2f” error signal • Signal 2xMI mod freq, dominates light on output PD • 2f represents optical gain of MI • allows much more frequent lock acquisition time (~ 1 min compared to ~ 1 day on SR signal) • Pre-lock reduces SR mirror motion • Switch to Proper SR error signal on zero crossing

  9. Tuning dual-recycled GEO600 • Initial SR detuning of ~5 kHz • Easier lock acquisition • Downtune to operating point • Automaticdetuning to 1.3 kHz in ~ 30 s (Data not valid during the downtuning) • Relavant gains, phases automatically adjusted by Labview system • Have tuned as low as 700 Hz

  10. Tunable optical gain

  11. S3 1-week duty cycle 100 99.2 98.1 99.5 93.6 98.8 77.9 locked 161.3 h unlocked 8.2 h longest lock 27.1 h Duty Cycle [%] Duty Cycle: 95.16 % Day

  12. Cause of loss of lock No Alignment feedback end of range 1 Seismic event 2 SR feedback saturation 1 Longitudinal Drift control for MSR added Heater with thermostat placed near to tank Modecleaner alignement jumps 1 Faulty contact found in MC electronics 8 North building temperature Not identified 3 Total 16 Lock losses (1 week) Investigations into causes of lock losses give:

  13. Sensitivity

  14. Lines in S3 h(t)

  15. Calibration line amplitude timeseries dominated by common low frequency noise! Calibration Line Amplitude Noise (I) • Noise at IFO output >> than input fluctuations • likely dominated by optical gain fluctuations

  16. Calibration Line Amplitude Noise (II) • Calibration line amplitude coherence with seismic and alignment channels @ double-freq microseism freq’s • Discovered in parallel by Bala, GEO++ mons • Likely optical gain fluctuations due to misalignment

  17. The Way Forward • Sensitivity improvement given highest priority • Removing lines • Pulsar hardware signal injections • Rejoin S3

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