1. Joshua Smith December 2003 Detector Characterization of Dual-Recycled GEO600 Joshua Smith for the GEO600 team

2. Joshua Smith December 2003 Optical layout Michelson Interferometer with Dual Recycling Folded arms with optical path length of 2400 m Mode Cleaners 2 triangular ring cavities (8 m optical path length each) Laser

3. Joshua Smith December 2003 Dual Recycling PR enhances carrier SR enhances signal MSR MPR Signal sidebands carrier

4. Joshua Smith December 2003 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. Joshua Smith December 2003 Excess mirror tilt Mirror tilt of ~1  rad @ pendulum resonances makes signal recycling lock acquisition very difficult Cause: Long to tilt coupling in monolithic suspensions Measured coherence: mirror tilt with ground motion along beam axis Understood, oversight in assembly

6. Joshua Smith December 2003 Reducing mirror tilt (I) Digital feedforward of ground motion to suspension point

7. Joshua Smith December 2003 Reducing mirror tilt (II) Applied digital FF correction for the tilt introduced by longitudinal feedback to intermediate mass

8. Joshua Smith December 2003 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. Joshua Smith December 2003 Tuning dual-recycled GEO600 Initial SR detuning of ~5 kHz Easier lock acquisition Downtune to operating point Automatic detuning 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. Joshua Smith December 2003 Tunable optical gain

11. Joshua Smith December 2003 S3 1-week duty cycle locked 161.3 h unlocked 8.2 h longest lock 27.1 h Duty Cycle: 95.16 % Day Duty Cycle [%] 10099.298.199.593.698.877.9

12. Joshua Smith December 2003 Lock losses (1 week) 16Total 3Not identified 8 North building temperature 1Modecleaner alignement jumps 1SR feedback saturation 2Seismic event 1Alignment feedback end of range NoCause of loss of lock Longitudinal Drift control for MSR added Faulty contact found in MC electronics Heater with thermostat placed near to tank Investigations into causes of lock losses give:

13. Joshua Smith December 2003 Sensitivity

14. Joshua Smith December 2003 Lines in S3 h(t)

15. Joshua Smith December 2003 Calibration Line Amplitude Noise (I) Noise at IFO output >> than input fluctuations likely dominated by optical gain fluctuations Calibration line amplitude timeseries dominated by common low frequency noise!

16. Joshua Smith December 2003 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. Joshua Smith December 2003 The Way Forward Sensitivity improvement given highest priority Removing lines Pulsar hardware signal injections Rejoin S3