LIGO-G000309-00-D

“First Lock” for the LIGO Detectors

20 October 2000 LIGO Hanford Observatory

Stan Whitcomb

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Outline

The LIGO Detectors

What is “Locking an Interferometer”?» Why do we need to do it?

» ….and why is it so difficult?

Evidence for Locking

The Next Steps

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LIGO Interferometer (Detector)

Laser

end test mass

2 km (4 km) Fabry-Perotarm cavity

recyclingmirror input test mass

beam splitter

Power RecycledMichelsonInterferometerwith Fabry-PerotArm Cavities

Power RecycledMichelsonInterferometerwith Fabry-PerotArm Cavities

signal

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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

Laser

signal

Gravitational wave changes arm lengths and amount of light in signal

Change in arm length is 10-18 meters,

or about 2/10000000000000000 inches

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How Small is 10-18 Meter

One meter, about 40 inches

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

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LIGO Interferometers

Laser

end test mass

Light bounces back and forth along arms about 100 times

input test massLight is “recycled” about 50 times

signal

Requires test masses to be held in position to 10-10 meter (atomic diameter)“Locking the interferometer”

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Why is Locking Difficult?

One meter, about 40 inches

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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Steps to Locking an Interferometer

signal

LaserX Arm

Y Arm

Composite Video

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Watching the Interferometer Lock

signal

X Arm

Y Arm

Laser

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Lock Duration

2 Minutes

Locked

Unlocked

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Where Do We Go From Here?

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

Change to X Arm» 2/12/00 18 minutes lock

» 3/4/00 90 minutes lock

» 3/26/00 10 hours lock

Start with Y Arm» 12/1/99 Flashes of light

» 12/9/99 0.2 seconds lock

» 1/14/00 2 seconds lock

» 1/19/00 60 seconds lock

» 1/21/00 5 minutes lock

Laser

Result of : -automatic alignment system -tuning electronics -reduction of noise sources

2 km Arm

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Extend the time that the interferometer locks» Goal is 40 hours, not seconds or minutes

Increase the sensitivity (reduce the noise)» Tune each subsystem for optimal performance

Where Do We Go From Here?

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Improvements in Laser Performance

Laser stability an important contributor to LIGO sensitivity

Steady improvement in laser noise performance

» electronics» acoustics» vibrations

Required

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Where Do We Go From Here?

Extend the time that the interferometer locks» Goal is 40 hours, not seconds or minutes

Increase the sensitivity (reduce the noise)» Tune each subsystem for optimal performance

Bring two more detectors on-line» Second detector here at Hanford Observatory

» Single detector at Livingston Observatory

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Summary

“Locking the Interferometer” marks a major transition for LIGO» Commissioning a full interferometer,

not individual subsystems

“First Lock” in the HanfordObservatorycontrol room

Akin to Wright brothers’ first flight

»It doesn’t stay up that long

»It isn’t very far off the ground

»But it does fly!