ï¿½ï¿½ï¿½first Lockï¿½ï¿½ï¿½ For The Ligo Detectors

“First Lock” for the LIGO Detectors
20 October 2000
LIGO Hanford Observatory
Stan Whitcomb
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Outline
l The LIGO Detectors
l What is “Locking an Interferometer”?
» Why do we need to do it?
» ….and why is it so difficult?
l Evidence for Locking
l The Next Steps
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LIGO Interferometer (Detector)
Power Recycled
Power Recycled
end test mass
Michelson
Michelson
Interferometer
Interferometer
with Fabry
with Fabry -
- Perot
Perot
2 km (4 km) Fabry-Perot
Arm Cavities
Arm Cavities
arm cavity
recycling
mirror
input test mass
Laser
signal
beam splitter
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Suspending the Test Masses (Mirrors)
vibration-isolated platform
initial alignment
test mass suspended on fine wire
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Sensing the Effect of a Gravitational Wave
Gravitational
wave changes
Change in arm length is
arm lengths
10-18 meters,
and amount of
or about
light in signal
2/10000000000000000 inches
Laser
signal
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How Small is 10-18 Meter
One meter, about 40 inches
÷ ,
10 000
Human hair, about 100 microns
÷100
Wavelength of light, about 1 micron
÷ ,
10 000
Atomic diameter, 10-10 meter
÷
,
100 000
Nuclear diameter, 10-15 meter
÷ ,
1 000
LIGO sensitivity, 10-18 meter
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LIGO Interferometers
Requires test masses to be
end test mass
held in position to 10-10
meter (atomic diameter)
“Locking the interferometer”
Light bounces back
and forth along arms
about 100 times
Light is “recycled”
about 50 times
input test mass
Laser
signal
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Why is Locking Difficult?
One meter, about 40 inches
÷ ,
10 000
Human hair, about 100 microns
Earthtides, about 100 microns
÷100
Wavelength of light, about 1 micron
Microseismic motion, about 1 micron
÷ ,
10 000
Atomic diameter, 10-10 meter
Precision required to lock, about 10-10 meter
÷
,
100 000
Nuclear diameter, 10-15 meter
÷ ,
1 000
LIGO sensitivity, 10-18 meter
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Steps to Locking an Interferometer
Composite Video
Y Arm
Laser
X Arm
signal
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Watching the Interferometer Lock
Y Arm
Laser
X Arm
signal
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Lock Duration
Locked
Unlocked
2 Minutes
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Where Do We Go From Here?
l Extend the time that the interferometer locks
» Goal is 40 hours, not seconds or minutes
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Extending the Lock on a Single Arm
2 km Arm
Laser
l Start with Y Arm
l Change to X Arm
» 12/1/99
Flashes of light
» 2/12/00 18 minutes lock
» 12/9/99
0.2 seconds lock
» 3/4/00
90 minutes lock
» 1/14/00
2 seconds lock
» 3/26/00
10 hours lock
» 1/19/00
60 seconds lock
» 1/21/00
5 minutes lock
Result of : -automatic alignment system
-tuning electronics
-reduction of noise sources
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Improvements in Laser Performance
l
Laser stability an
important contributor
Required
to LIGO sensitivity
l
Steady improvement
in laser noise
performance
» electronics
» acoustics
» vibrations
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Where Do We Go From Here?
l Extend the time that the interferometer locks
» Goal is 40 hours, not seconds or minutes
l Increase the sensitivity (reduce the noise)
» Tune each subsystem for optimal performance
l Bring two more detectors on-line
» Second detector here at Hanford Observatory
» Single detector at Livingston Observatory
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Summary
l “Locking the Interferometer” marks a
major transition for LIGO
“First Lock”
in the Hanford
» Commissioning a full interferometer,
Observatory
not individual subsystems
control room
lAkin to Wright brothers’
first flight
»It doesn’t stay up that long
»It isn’t very far off the ground
»But it does fly!
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