joshua smith december 2003 detector characterization of dual-recycled geo600 joshua smith for the...
TRANSCRIPT
Joshua Smith December 2003
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 opticalpath length of 2400 m
Mode Cleaners
2 triangular ringcavities (8 m opticalpath length each)
Laser
Joshua Smith December 2003
Dual Recycling
• PR enhances carrier
• SR enhances signal
MSR
MPR Signal sidebands
carrier
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 ~1rad @ 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
S3 1-week duty cycle
locked 161.3 h
unlocked 8.2 h
longest lock 27.1 hDuty Cycle:
95.16 %
Day
Dut
y C
ycle
[%
]
100 99.2 98.1 99.5 93.6 98.8 77.9
Joshua Smith December 2003
Lock losses (1 week)
16Total
3Not identified
8North 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:
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