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Gravitational Waves Laser Interferometric Detectors: 

Gravitational Waves Laser Interferometric Detectors Barry Barish 5 July 2000 The Ninth Marcel Grossmann Meeting University of Rome “La Sapienza” Rome, July 2 - 8, 2000

Slide2: 

Suspended mass Michelson-type interferometers on earth’s surface detect distant astrophysical sources International network (LIGO, Virgo, GEO, TAMA and AIGO) enable locating sources and decomposing polarization of gravitational waves. Interferometers terrestrial Suspended test masses

Interferomersinternational network: 

Interferomers international network LIGO Simultaneously detect signal (within msec) detection confidence locate the sources decompose the polarization of gravitational waves GEO Virgo TAMA AIGO

Slide4: 

LIGO (Washington) LIGO (Louisiana) Interferometers international network

Slide5: 

GEO 600 (Germany) Virgo (Italy) Interferometers international network

Slide6: 

TAMA 300 (Japan) AIGO (Australia) Interferometers international network

Astrophysics Sourcesfrequency range: 

Astrophysics Sources frequency range EM waves are studied over ~20 orders of magnitude (ULF radio -> HE  rays) Gravitational Waves over ~8 orders of magnitude (terrestrial + space) Audio band space groundbased

Interferometers the noise floor: 

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

Noise Floor40 m prototype: 

Noise Floor 40 m prototype displacement sensitivity in 40 m prototype. comparison to predicted contributions from various noise sources

Slide10: 

Noise Floor TAMA 300

Vacuum Systemsbeam tube enclosures: 

Vacuum Systems beam tube enclosures LIGO minimal enclosures no services Virgo preparing arms GEO tube in the trench

Beam Tubes: 

Beam Tubes LIGO 4 km beam tube (1998) TAMA 300 m beam pipe

Beam Tube Bakeout: 

Beam Tube Bakeout LIGO bakeout standard quantum limit phase noise residual gas

BakeoutLIGO performance: 

Bakeout LIGO performance Achieved Design Requirements (< 10-9 torr) partial pressures during bakeout

Vacuum Chamberstest masses, optics: 

Vacuum Chambers test masses, optics TAMA chambers LIGO chambers

Interferometers the noise floor: 

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

Slide17: 

Suspension vertical transfer function measured and simulated (prototype) Seismic Isolation Virgo “Long Suspensions” inverted pendulum five intermediate filters

Slide18: 

Long Suspensions Virgo installation at the site Beam Splitter and North Input mirror All four long suspensions for the entire central interferometer will be complete by October 2000.

Slide19: 

Suspensions GEO triple suspension lower cantilever stage (view from below)

Suspensions GEO triple pendulum : 

Suspensions GEO triple pendulum

Slide21: 

Test Masses fibers and bonding - GEO

Interferometers basic optical configuration: 

Interferometers basic optical configuration

Opticsmirrors, coating and polishing: 

Optics mirrors, coating and polishing All optics polished & coated Microroughness within spec. (<10 ppm scatter) Radius of curvature within spec. (dR/R < 5%) Coating defects within spec. (pt. defects < 2 ppm, 10 optics tested) Coating absorption within spec. (<1 ppm, 40 optics tested) LIGO

LIGOmetrology: 

LIGO metrology Caltech CSIRO

Slide25: 

Corrective Coating Virgo

Slide26: 

Corrective Coating results 6 nm R.M.S. 1,5 nm R.M.S. Before After 80 mm high reflectivity mirror @633 nm

Interferometers the noise floor: 

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

Interferometers Lasers: 

Interferometers Lasers Nd:YAG (1.064 mm) Output power > 8W in TEM00 mode GEO Laser LIGO Laser master oscillator power amplifier Master-Slave configuration with 12W output power Virgo Laser residual frequency noise

Laser pre-stabilization: 

Laser pre-stabilization intensity noise: dI(f)/I <10-6/Hz1/2, 40 Hz<f<10 KHz frequency noise: dn(f) < 10-2Hz/Hz1/2 40Hz<f<10KHz

Phase Noisesplitting the fringe: 

Phase Noise splitting 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

Slide31: 

Interferometers sensitivity curves TAMA 300 GEO 600 Virgo LIGO

Interferometerstesting and commissioning : 

Interferometers testing and commissioning TAMA 300 interferometer locked; noise studies LIGO input optics commissioned; 2 km single arm locked/tested Geo 600 commissioning tests Virgo testing isolation systems; input optics AIGO setting up central facility

Slide33: 

TAMA 300 optical configuration

Slide34: 

TAMA Commissioning control error signals

Slide35: 

TAMA Performance noise source analysis

LIGOschematic of interferometer system: 

LIGO schematic of interferometer system LASER Mode Cleaner 2 km cavity

2km Fabry-Perot cavity: 

2km Fabry-Perot cavity Includes all interferometer subsystems many in definitive form; analog servo on cavity length for test configuration confirmation of initial alignment ~100 microrad errors; beams easily found in both arms ability to lock cavity improves with understanding 0 sec 12/1 flashes of light 0.2 sec 12/9 2 min 1/14 60 sec 1/19 5 min 1/21 (and on a different arm) 18 min 2/12 1.5 hrs 3/4 (temperature stabilize pre modecleaner)

2km Fabry-Perot cavity: 

2km Fabry-Perot cavity models of environment temperature changes on laser frequency tidal forces changing baselines seismometer/tilt correlations with microseismic peak mirror characterization losses: ~6% dip, excess probably due to poor centering scatter: appears to be better than requirements figure 12/03 beam profile

Slide39: 

2km Fabry-Perot cavity 15 minute locked stretch

Interferometersastrophysical sources: 

Interferometers astrophysical sources Compact binary mergers Sensitivity to coalescing binaries Binary inspiral ‘chirp’ signal 2002 2007 future

Interferometerdata analysis: 

Interferometer data 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

Interferometer Data40 m : 

Interferometer Data 40 m Real interferometer data is UGLY!!! (Gliches - known and unknown) LOCKING RINGING NORMAL ROCKING

The Problem: 

The Problem How much does real data degrade complicate the data analysis and degrade the sensitivity ?? Test with real data by setting an upper limit on galactic neutron star inspiral rate using 40 m data

“Clean up” data stream: 

“Clean up” data stream Effect of removing sinusoidal artifacts using multi-taper methods Non stationary noise Non gaussian tails

Inspiral ‘Chirp’ Signal: 

Inspiral ‘Chirp’ Signal Template Waveforms “matched filtering” 687 filters 44.8 hrs of data 39.9 hrs arms locked 25.0 hrs good data sensitivity to our galaxy h ~ 3.5 10-19 mHz-1/2 expected rate ~10-6/yr

Detection Efficiency: 

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

Setting a limit: 

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 e = 0.33 = detection efficiency An ideal detector would set a limit: R < 0.16/hour

Slide48: 

TAMA 300 search for binary coalescence 2-step hierarchical method chirp masses (0.3-10)M0 strain calibrated dh/h ~ 1 % Matched templates

Slide49: 

TAMA 300 preliminary result For signal/noise = 7.2 Expect: 2.5 events Observe: 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.

Interferometersastrophysical sources: 

Interferometers astrophysical sources SN1987A sensitivity to burst sources

LIGOastrophysical sources: 

LIGO astrophysical sources Pulsars in our galaxy non axisymmetric: 10-4 < e < 10-6 science: neutron star precession; interiors narrow band searches best Continuous wave sources

Conclusions: 

Conclusions a new generation of 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 (see Tsubono) science data taking to begin within two years plans and agreements being made for exchange of data for coincidences between detectors (GWIC) significant improvements in sensitivity (h ~ 10-22) are anticipated about 2007+ (see Danzmann)