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 mMode 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 tiltwith

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

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

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