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First Generation Interferometers

Learn about the detection of gravitational waves using interferometers, noise sources, sensitive regions, and vacuum systems discussed at Drexel University workshop. Discover advancements in Astrophysical Sources and Precision Instruments.

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First Generation Interferometers

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  1. Workshop on Astrophysical Sources for Ground-Based Gravitational Wave Detectors Drexel University First Generation Interferometers Barry Barish 30 Oct 2000

  2. Detection of Gravitational Waves precision 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

  3. Interferometersthe 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

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

  5. Interferometers international network LIGO (Washington) LIGO (Louisiana)

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

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

  8. Interferometersthe 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

  9. 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

  10. Noise Floor40 m prototype • displacement sensitivity • in 40 m prototype. • comparison to predicted contributions from various noise sources

  11. Noise Floor TAMA 300

  12. Interferometersthe 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

  13. Vacuum Systemsbeam tube enclosures LIGO minimal enclosures no services Virgo preparing arms GEO tube in the trench

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

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

  16. Vacuum Chamberstest masses, optics LIGO chambers TAMA chambers

  17. Interferometersthe 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

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

  19. Long Suspensions Virgo installation at the site Beam Splitter and North Input mirror All four long suspensions for the entire central interferometer

  20. SuspensionsGEO triple pendulum

  21. Test Masses fibers and bonding - GEO

  22. Interferometersbasic optical configuration

  23. Opticsmirrors, coating and polishing LIGO • 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)

  24. LIGOmetrology • Caltech • CSIRO

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

  26. Prestabalized Laserperformance • > 18,000 hours continuous operation • Frequency and lock very robust • TEM00 power > 8 watts • Non-TEM00 power < 10%

  27. Interferometers sensitivity curves TAMA 300 Virgo LIGO GEO 600

  28. 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

  29. TAMA Performance noise source analysis

  30. TAMA Performance noise source analysis

  31. TAMA 2 week data run 21 Aug to 4 Sept 00 • best sensitivity: • 5x10-21 Hz-1/2 (~ 1kHz) • interferometer stability; • longest lock > 12 hrs • non-stationary noise • significantly reduced • auxiliary signals • approx 100 signals including feedback and error signals and environmental signals were recorded • plans • two-month data run planned for Jan 2001; signal recycling added next year.

  32. LIGOcommissioning • Mode cleaner and Pre-Stabilized Laser • 2km one-arm cavity • short Michelson interferometer studies • Lock entire Michelson Fabry-Perot interferometer “FIRST LOCK”

  33. 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

  34. 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 LIGOlocking a 2km arm First interference fringes from the 2-km arm

  35. 2km Fabry-Perot cavity 15 minute locked stretch

  36. Near-Michelson interferometer • power recycled (short) Michelson Interferometer • employs full mixed digital/analog servos Interference fringes from the power recycled near Michelsoninterferometer

  37. Composite Video LIGO first lock Y Arm Laser X Arm signal

  38. 2 min LIGObrief locked stretch Y arm X arm Reflected light Anti-symmetricport

  39. 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

  40. Interferometer Data40 m Real interferometer data is UGLY!!! (Gliches - known and unknown) LOCKING NORMAL RINGING ROCKING

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

  42. 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

  43. 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

  44. 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

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

  46. TAMA 300 preliminary result For signal/noise = 7.2 Expect: 2.5 events Observe: 2 events Rate < 0.59 ev/hr 90% C.L. Note: for a 1.4 M0 NS-NS inspiral this limit corresponds to a max distance = 6.2 kpc

  47. 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+

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