Detector Characterization of Dual-Recycled GEO600 Joshua Smith for - PowerPoint PPT Presentation

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

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

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

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

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

Tunable optical gain Joshua Smith December 2003

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 Duty Cycle [%] h longest lock 27.1 h Duty Cycle: 95.16 % Day Joshua Smith December 2003

Lock losses (1 week) Investigations into causes of lock losses give: Cause of loss of lock No Alignment feedback end of range 1 Seismic event 2 Longitudinal Drift control for MSR added SR feedback saturation 1 Faulty contact found in Modecleaner alignement jumps 1 MC electronics 8 North building temperature Heater with thermostat placed near to tank Not identified 3 Total 16 Joshua Smith December 2003

Sensitivity Joshua Smith December 2003

Lines in S3 h(t) 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! 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 Joshua Smith December 2003

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