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First Generation Interferometers

Barry Barish

30 Oct 2000

Workshop on Astrophysical Sources for Ground-Based

Gravitational Wave Detectors

Drexel University

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Detection of Gravitational Wavesprecision optical instrument

• detect a stretch (squash) of 10-18 m !! ( a small fraction of the size of a proton)

• first generation interferometers will have strain sensitivity h ~ 10-21 for 10Hz < f < 10KHz

• time frame 2001-2006, then upgrades to improve sensitivity (Fritschel)

LIGO interferometer

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Interferometers the noise floor

Interferometry is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies

Many other noise sources lurk underneath and must be controlled as the instrument is improved

Sensitive region

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Interferomersinternational network

LIGO

Simultaneously detect signal (within msec)

detection confidence locate the sources

decompose the polarization of gravitational waves

GEO VirgoTAMA

AIGO

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LIGO (Washington) LIGO (Louisiana)

Interferometersinternational network

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GEO 600 (Germany) Virgo (Italy)

Interferometersinternational network

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TAMA 300 (Japan) AIGO (Australia)

Interferometersinternational network

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Interferometers the noise floor

Interferometry is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies

Many other noise sources lurk underneath and must be controlled as the instrument is improved

Sensitive region

shot

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Phase Noisesplitting the fringe

• spectral sensitivity of MIT phase noise interferometer

• above 500 Hz shot noise limited near LIGO I goal

• additional features are from 60 Hz powerline harmonics, wire resonances (600 Hz), mount resonances, etc

shot noise

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Noise Floor40 m prototype

• displacement sensitivityin 40 m prototype. • comparison to predicted contributions from various noise sources

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Noise FloorTAMA 300

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Interferometers the noise floor

Interferometry is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies

Many other noise sources lurk underneath and must be controlled as the instrument is improved

Sensitive region

vacuum

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Vacuum Systemsbeam tube enclosures

LIGO minimal enclosures

no services

Virgopreparing arms

GEOtube in the trench

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Beam Tubes

LIGO 4 km beam tube (1998)

TAMA 300 m beam pipe

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Beam Tube Bakeout

LIGO bakeout

standard quantum limit

phase noise

residual gas

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Vacuum Chamberstest masses, optics

TAMA chambers

LIGO chambers

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Interferometers the noise floor

Interferometry is limited by three fundamental noise sources

seismic noise at the lowest frequencies thermal noise at intermediate frequencies shot noise at high frequencies

Many other noise sources lurk underneath and must be controlled as the instrument is improved

Sensitive region

seismic

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Suspension vertical transfer function measured and simulated (prototype)

Seismic IsolationVirgo

“Long Suspensions”• inverted pendulum• five intermediate filters

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Long SuspensionsVirgo installation at the site

Beam Splitter and North Input mirror

All four long suspensions for the entire central interferometer

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Suspensions GEO triple pendulum

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Test Massesfibers and bonding - GEO

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Interferometers basic optical configuration

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Opticsmirrors, coating and polishing

All optics polished & coated» Microroughness within spec.

(<10 ppm scatter)» Radius of curvature within

spec. R/R 5%)» Coating defects within spec.

(pt. defects < 2 ppm, 10 optics tested)

» Coating absorption within spec. (<1 ppm, 40 optics tested)

LIGO

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LIGOmetrology

Caltech

CSIRO

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Interferometers lasers

Nd:YAG (1.064 m) Output power > 8W in

TEM00 mode

GEO Laser

LIGO Lasermaster oscillator power amplifier

Master-Slave configuration with 12W output power

Virgo Laser

residual frequency noise

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Prestabalized Laser performance

> 18,000 hours continuous operation

Frequency and lock very robust

TEM00 power > 8 watts

Non-TEM00 power < 10%

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1 10 100 100010

-23

10-22

10-21

10-20

10-19

10-18

C85 steel wire (total) Fused Silica wire (total) FS pendulum thermal noise Mirror thermal noise

h [1

/sqr

t(H

z)]

Frequency [Hz]

Virgo sensitivity curveInterferometerssensitivity curves

TAMA 300

GEO 600

Virgo

LIGO

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Interferometerstesting and commissioning

TAMA 300» interferometer locked; noise/robustness improved; successful two week data run (Aug 00)

LIGO» subsystems commissioned; » 2 km first lock (Nov 00)

Geo 600» commissioning tests

Virgo» testing isolation systems; commissioning input optics

AIGO» setting up central facility; short arm interferometer

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TAMA Performancenoise source analysis

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TAMA Performancenoise source analysis

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• best sensitivity: 5x10-21 Hz-1/2 (~ 1kHz)

• interferometer stability; longest lock > 12 hrs

• non-stationary noise significantly reduced • auxiliary signalsapprox 100 signals including feedback and error signals and environmental signals were recorded

• planstwo-month data run planned for Jan 2001; signal recycling added next year.

TAMA2 week data run

21 Aug to 4 Sept 00

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LIGOcommissioning

Mode cleaner and Pre-Stabilized Laser 2km one-arm cavity short Michelson interferometer studies

Lock entire Michelson Fabry-Perot interferometer

“FIRST LOCK”

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Detector Commissioning: 2-km Arm Test

12/99 – 3/00

Alignment “dead reckoning” worked

Digital controls, networks, and software all worked

Exercised fast analog laser frequency control

Verified that core optics meet specs

Long-term drifts consistent with earth tides

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LIGOlocking a 2km 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

(on other arm) 2/12/00 18 minutes lock 3/4/00 90 minutes lock

(temperature stabilized laser reference cavity)

3/26/00 10 hours lock

First interference fringesfrom the 2-km arm

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2km Fabry-Perot cavity 15 minute locked stretch

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Near-Michelson interferometer

Interference fringes from thepower recycled near Michelsoninterferometer

• power recycled (short) Michelson Interferometer

• employs full mixed digital/analog servos

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LIGOfirst lock

signal

LaserX Arm

Y Arm

Composite Video

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LIGObrief locked stretch

X arm

Reflectedlight

Y arm

Anti-symmetricport

2 min

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Interferometerdata analysis

Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms » search technique: matched templates

Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in electromagnetic radiation » prompt alarm (~ one hour) with neutrino detectors

Pulsars in our galaxy: “periodic”» search for observed neutron stars (frequency, doppler shift)» all sky search (computing challenge)» r-modes

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Interferometer Data40 m

Real interferometer data is UGLY!!!(Gliches - known and unknown)

LOCKING

RINGING

NORMAL

ROCKING

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“Clean up” data stream

Effect of removing sinusoidal artifacts using multi-taper methods

Non stationary noise Non gaussian tails

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Inspiral ‘Chirp’ Signal

Template Waveforms

“matched filtering”687 filters

44.8 hrs of data39.9 hrs arms locked25.0 hrs good data

sensitivity to our galaxyh ~ 3.5 10-19 mHz-1/2

expected rate ~10-6/yr

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Detection Efficiency

• Simulated inspiral events provide end to end test of analysis and simulation code for reconstruction efficiency

• Errors in distance measurements from presence of noise are consistent with SNR fluctuations

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Setting a limit

Upper limit on event rate can be determined from SNR of ‘loudest’ event

Limit on rate:R < 0.5/hour with 90% CL = 0.33 = detection efficiency

An ideal detector would set a limit:R < 0.16/hour

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TAMA 300search for binary coalescence

• 2-step hierarchical method

• chirp masses (0.3-10)M0

• strain calibrated h/h ~ 1 %

Matched templates

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TAMA 300preliminary result

For signal/noise = 7.2

Expect: 2.5 eventsObserve: 2 events

Note: for a 1.4 M0 NS-NS inspiral this limit corresponds to a max distance = 6.2 kpc

Rate < 0.59 ev/hr 90% C.L.

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Conclusions First generation long baseline suspended mass

interferometers are being completed with h ~ 10-21

commissioning, testing and characterization of the interferometers is underway

data analysis schemes are being developed, including tests with real data from the 40 m prototype and TAMA

science data taking to begin soon – TAMA ; then LIGO (2002)

plans and agreements being made for exchange of data for coincidences between detectors (GWIC)

Second generation - significant improvements in sensitivity

(h ~ 10-22) are anticipated about 2007+