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

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Dec 05, 2022 359 likes •542 views

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

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Joshua Smith December 2003

Detector Characterization of Dual-Recycled GEO600

Joshua Smith for the GEO600 team

SLIDE 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

SLIDE 3

Joshua Smith December 2003

Dual Recycling

PR enhances carrier
SR enhances signal

MSR MPR

Signal sidebands carrier

SLIDE 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

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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

SLIDE 6

Joshua Smith December 2003

Reducing mirror tilt (I)

Digital feedforward of ground motion to suspension point

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Joshua Smith December 2003

Reducing mirror tilt (II)

Applied digital FF correction for the tilt introduced by

longitudinal feedback to intermediate mass

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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

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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

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Joshua Smith December 2003

Tunable optical gain

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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 [%] 100 99.2 98.1 99.5 93.6 98.8 77.9

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Joshua Smith December 2003

Lock losses (1 week)

16 Total 3 Not identified 8 North building temperature 1 Modecleaner alignement jumps 1 SR feedback saturation 2 Seismic event 1 Alignment feedback end of range No Cause 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:

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Joshua Smith December 2003

Sensitivity

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Joshua Smith December 2003

Lines in S3 h(t)

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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!

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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

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Joshua Smith December 2003

The Way Forward

Sensitivity improvement given highest priority
Removing lines
Pulsar hardware signal injections
Rejoin S3