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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LIGO-G050478-00-W Commissioning and Performance of the LIGO Interferometers Reported on behalf of LIGO colleagues by Fred Raab, LIGO Hanford Observatory.
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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
• 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
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