ligo-g050478-00-w commissioning and performance of the ligo interferometers reported on behalf of...
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LIGO-G050478-00-W
Commissioning and Performance of the LIGO Interferometers
Reported on behalf of LIGO colleagues by
Fred Raab, LIGO Hanford Observatory
(Substituting for Brian O’Reilly, LIGO Livingston Observatory, whose trip was cancelled by Hurricane
Katrina)
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Time Line
NowInauguration
1999 2000 2001 2002 20033 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
E2Engineering
E3 E5 E9 E10E7 E8 E11
First Lock Full Lock all IFO
10-17 10-18 10-20 10-21
2004 20051 2 3 4 1 2 3 4 1 2 3 4
2006
Runs
First Science Data
S1 S4Science
S2 S3 S5
10-224K strain noise at 150 Hz [Hz-1/2]
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Schematic of Initial LIGO Detector (LIGO-1)
suspended mirrors markinertial frames
antisymmetric portcarries GW signal
Symmetric port carriescommon-mode info
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What Limits Sensitivityof Interferometers?
• Seismic noise & vibration limit at low frequencies
• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at high frequencies
• Myriad details of the lasers, electronics, etc., can make problems above these levels
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Vibration Isolation Systems
» Reduce in-band seismic motion by 4 - 6 orders of magnitude» Little or no attenuation below 10Hz» Large range actuation for initial alignment and drift compensation» Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during
observation
HAM Chamber BSC Chamber
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Core Optics
Substrates: SiO2
» 25 cm Diameter, 10 cm thick
» Homogeneity < 5 x 10-7
» Internal mode Q’s > 2 x 106
Polishing» Surface uniformity < 1 nm rms
» Radii of curvature matched < 3%
Coating» Scatter < 50 ppm
» Absorption < 2 ppm
» Uniformity <10-3
Production involved 6 companies, NIST, and LIGO
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Core Optics Suspension and Control
Shadow sensors & voice-coil actuators provide
damping and control forces
Mirror is balanced on 30 microndiameter wire to 1/100th degree of arc
Optics suspended as simple pendulums
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Pre-stabilized Laser (PSL)
Custom-built10 W Nd:YAG Laser,
joint development with Lightwave Electronics
(now commercial product)
Frequency reference cavity (inside oven)
Cavity for defining beam geometry,
joint development withStanford
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IO
Frequency Stabilization of the Light Employs Three Stages
Pre-stabilized laser delivers light to the long mode cleaner
• Start with high-quality, custom-built Nd:YAG laser
• Improve frequency, amplitude and spatial purity of beam
Actuator inputs provide for further laser stabilization
• Wideband• Tidal
10-WattLaser
PSL Interferometer
15m4 km
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Feedback & Control for Mirrors and Light
Damp suspended mirrors to vibration-isolated tables» 14 mirrors (pos, pit, yaw, side) = 56 loops
Damp mirror angles to lab floor using optical levers» 7 mirrors (pit, yaw) = 14 loops
Pre-stabilized laser» (frequency, intensity, pre-mode-cleaner) = 3 loops
Cavity length control» (mode-cleaner, common-mode frequency, common-arm, differential
arm, michelson, power-recycling) = 6 loops
Wave-front sensing/control» 7 mirrors (pit, yaw) = 14 loops
Beam-centering control» 2 arms (pit, yaw) = 4 loops
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Input Matrix Decodes Input into DARM, CARM, MICH, PRC
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Output Matrix Translates Loop Feedback into Actuator Signals
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Digital Controls screen example A
nal
og
In
An
alo
g O
ut
Digital calibration input
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LIGO Sensitivity Over TimeLivingston 4km Interferometer
May 01
Jan 03
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Why is Locking Difficult?
One meter
Human hair, about 100 microns000,10
Wavelength of light, about 1 micron100
LIGO sensitivity, 10-18 meter000,1
Nuclear diameter, 10-15 meter000,100
Atomic diameter, 10-10 meter000,10
Earthtides, about 100 microns
Microseismic motion, about 1 micron
Precision required to lock, about 10-10 meter
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Run S3 S4
L1 21.8% 74.5%
H1 69.3% 80.5%
H2 63.4% 81.4%
Triple 15.8% 56.9%
Progress: Duty Cycle
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Improved Isolation with the Hydraulic External Pre-Isolator (HEPI)
Adv. LIGO approach, accelerated & adapted for use in initial LIGO
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HAM
BSC
Active External Pre-Isolators
Seismic Retrofit at Livingston
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One-Arm Test of External Pre-Isolation Confirms Performance
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Thermal Compensation
Over-heat Correction
Inhomogeneous Correction
Under-heat Correction
CO2
Laser
?
ZnSe Viewport Over-heat pattern
Inner radius = 4cm Outer radius =11cm
Cold power recycling cavity is unstable: poor buildup and mode shape for the RF sidebands
ITM thermal lens power of ~0.00003 diopters needed to achieve a stable, mode-matched cavity
intended to be produced by ~25 mW absorbed from 1μm beam
ITM
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Sideband Images as Function of Thermal Heating
No Heating 30 mW 60 mW 90 mW
120 mW 150 mW 180 mW Input beam
Best match
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101
102
10-19
10-18
10-17
10-16
10-15
10-14
Frequency [Hz]
Dis
pla
ce
me
nt
[m/
Hz]
L1: 8.9 Mpc, Aug 12 2005 05:48:43 UTC
L-Mirror ThermalWire ThermalDark NoiseIntensity NoiseFrequency NoiseShot NoiseLocal DampingSeismicPRC -> DARMMICH -> DARMOscillator PhaseOptical LeversWFSETM electronicsITM electronicsTotalRequirement
Close-up of estimated noise sources for L1
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Ongoing story of photodiode damage
Loss-of-lock: full beamsplitter power can be dumped out the AS port, in a ~10 msec width pulse
» Mechanical shutter cuts off the beam, with a trigger delay of about 6 msec
PD damage due to» Too high trigger level» Shutter too slow (wrong type)
Damaged PDs can be noisy Solution (in progress):
» All shutters of proper type» Carefully set trigger level» Looking at cutting off PD bias
voltage on lock-loss
~100 W
5 msec
Red: replaced damaged PDs
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Upconversion from stack motion
Using HEPI, increase the suspension point motion at 1.5 Hz by a factor of 5
DARM noise increases by a factor of ~5 over a wide band
Effect first seen at LHO, & measured recently at LLO:
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Scattered light fringe wrappingB
RT
ITMETM
Esc~10 -10 E0
)sin( sct
Data looks a lot like what you’d expect from scattered light Don’t know where light is scattering off Beam tube baffles were made to cut stray rays: 270 mm
aperture May be possible to use feedback to reduce optical table motion
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Closing remarks…
Progressive sensitivity improvements have achieved design goals
Early implementation of Advance LIGO techniques helped achieve goals» HEPI for duty-cycle boost
» Thermal compensation of mirrors for high-power operation
Some technical issues being worked to improve long-term robustness and reliability» Loss-of-lock protection for photodiodes
» Upconversion mitigation
Believe still room for post-S5 improvements
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