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The Status of Gravitational-Wave Detectors, Especially LIGO

The Status of Gravitational-Wave Detectors, Especially LIGO. "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA). Reported on behalf of LIGO colleagues by Fred Raab, LIGO Hanford Observatory. LIGO’s Mission is to Open a New Portal on the Universe.

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The Status of Gravitational-Wave Detectors, Especially LIGO

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  1. The Status of Gravitational-Wave Detectors, Especially LIGO "Colliding Black Holes"Credit:National Center for Supercomputing Applications (NCSA) Reported on behalf of LIGO colleagues by Fred Raab, LIGO Hanford Observatory

  2. LIGO’s Mission is to Open a New Portal on the Universe • In 1609 Galileo viewed the sky through a 20X telescope and gave birth to modern astronomy • LIGO’s quest is to create a radically new way to perceive the universe, by directly listening to the vibrations of space itself • LIGO consists of large, earth-based, detectors that will act like huge microphones, listening for “spacequakes” from the most violent events in the universe Raab: Status of GW Detectors, Especially LIGO

  3. Different Frequency Bands of Detectors and Sources space terrestrial Audio band • EM waves are studied over ~20 orders of magnitude • (ULF radio -> HE  rays) • Gravitational Wave coverage planned to cover ~8 orders of magnitude • (terrestrial + space) Raab: Status of GW Detectors, Especially LIGO

  4. Gravitational Collapse and Its Outcomes Present LIGO Opportunities fGW > few Hz accessible from earth fGW < several kHz interesting for compact objects Raab: Status of GW Detectors, Especially LIGO

  5. Catching Waves FromOrbiting Black Holes and Neutron Stars Sketches courtesy of Kip Thorne Raab: Status of GW Detectors, Especially LIGO

  6. Gravitational Waves the evidence Emission of gravitational waves Neutron Binary System – Hulse & Taylor PSR 1913 + 16 -- Timing of pulsars 17 / sec · · ~ 8 hr • Neutron Binary System • separated by 106 miles • m1 = 1.4m; m2 = 1.36m; e = 0.617 • Prediction from general relativity • spiral in by 3 mm/orbit • rate of change orbital period Raab: Status of GW Detectors, Especially LIGO

  7. How does LIGO detect spacetime vibrations? Leonardo da Vinci’s Vitruvian man

  8. Basic Signature of Gravitational Waves for All Detectors Raab: Status of GW Detectors, Especially LIGO

  9. AURIGA II Resonant Bar Detector LHe4 vessel Al2081 holder Electronics wiring support Main Attenuator Thermal Shield Sensitive bar Compression Spring Transducer Original Terrestrial Detectors (Continue to be Improved) • Efforts to broaden frequency range and reduce noise • Size limited by sound speed Courtesy M. Cerdonnio Raab: Status of GW Detectors, Especially LIGO

  10. New Generation of “Free-Mass” Detectors Now Online suspended mirrors mark inertial frames antisymmetric port carries GW signal Symmetric port carries common-mode info Intrinsically broad band and size-limited by speed of light. Raab: Status of GW Detectors, Especially LIGO

  11. The International Interferometer Network Simultaneously detect signal (within msec) Virgo GEO LIGO TAMA detection confidence locate the sources decompose the polarization of gravitational waves AIGO Raab: Status of GW Detectors, Especially LIGO

  12. The Laser Interferometer Gravitational-Wave Observatory LIGO (Washington) (4-km and 2km) LIGO (Louisiana) (4-km) Funded by the National Science Foundation; operated by Caltech and MIT; the research focus for more than 500 LIGO Scientific Collaboration members worldwide. Raab: Status of GW Detectors, Especially LIGO

  13. Interferometers in Europe GEO 600 (Germany) (600-m) Virgo (Italy) 3-km Raab: Status of GW Detectors, Especially LIGO

  14. Interferometers in Asia, Australia TAMA 300 (Japan) (300-m) AIGO (Australia) (80-m, but 3-km site Raab: Status of GW Detectors, Especially LIGO

  15. Bar Network: Int’l Gravitational Event Collaboration Network of the 5 bar detectors almost parallel ALLEGRO NFS-LSUhttp://gravity.phys.lsu.edu AURIGA INFN-LNL http://www.auriga.lnl.infn.it NIOBE ARC-UWA http://www.gravity.pd.uwa.edu.au EXPLORER INFN-CERN http://www.roma1.infn.it/rog/rogmain.html NAUTILUS INFN-LNF Raab: Status of GW Detectors, Especially LIGO

  16. Spacetime is Stiff! => Wave can carry huge energy with miniscule amplitude! h ~ (G/c4) (ENS/r) Raab: Status of GW Detectors, Especially LIGO

  17. Some of the Technical Challenges • Typical Strains < 10-21 at Earth ~ 1 hair’s width at 4 light years • Understand displacement fluctuations of 4-km arms at the millifermi level (1/1000th of a proton diameter) • Control arm lengths to 10-13 meters RMS • Detect optical phase changes of ~ 10-10 radians • Hold mirror alignments to 10-8 radians • Engineer structures to mitigate recoil from atomic vibrations in suspended mirrors Raab: Status of GW Detectors, Especially LIGO

  18. What Limits Sensitivityof Interferometers? • Seismic noise & vibration limit at low frequencies • Atomic vibrations (Thermal Noise) inside components limit at mid frequencies • Quantum nature of light (Shot Noise) limits at high frequencies • Myriad details of the lasers, electronics, etc., can make problems above these levels Raab: Status of GW Detectors, Especially LIGO

  19. 1999 2003 2000 2002 2001 4Q 3Q 2Q 2Q 2Q 2Q 4Q 4Q 4Q 4Q 1Q 1Q 1Q 1Q 3Q 3Q 3Q 3Q Full Lock all IFO's First Lock Inauguration 10-22 10-21 S1 S2 S3 Science Time Line Now strain noise density @ 200 Hz [Hz-1/2] 10-17 10-18 10-19 10-20 E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 Engineering Runs First Science Data Raab: Status of GW Detectors, Especially LIGO

  20. Despite a few difficulties, science runs started in 2002. Raab: Status of GW Detectors, Especially LIGO

  21. Vibration Isolation Systems • Reduce in-band seismic motion by 4 - 6 orders of magnitude • Little or no attenuation below 10Hz • Large range actuation for initial alignment and drift compensation • Quiet actuation to correct for Earth tides and microseism at 0.15 Hz during observation BSC Chamber HAM Chamber Raab: Status of GW Detectors, Especially LIGO

  22. damped springcross section Seismic Isolation – Springs and Masses Raab: Status of GW Detectors, Especially LIGO

  23. 102 100 10-2 10-6 Horizontal 10-4 10-6 10-8 Vertical 10-10 Seismic System Performance HAM stack in air BSC stackin vacuum Raab: Status of GW Detectors, Especially LIGO

  24. Core Optics Suspension and Control Optics suspended as simple pendulums Shadow sensors & voice-coil actuators provide damping and control forces Mirror is balanced on 30 micron diameter wire to 1/100th degree of arc Raab: Status of GW Detectors, Especially LIGO

  25. Feedback & Control for Mirrors and Light • Damp suspended mirrors to vibration-isolated tables • 14 mirrors  (pos, pit, yaw, side) = 56 loops • Damp mirror angles to lab floor using optical levers • 7 mirrors  (pit, yaw) = 14 loops • Pre-stabilized laser • (frequency, intensity, pre-mode-cleaner) = 3 loops • Cavity length control • (mode-cleaner, common-mode frequency, common-arm, differential arm, michelson, power-recycling) = 6 loops • Wave-front sensing/control • 7 mirrors  (pit, yaw) = 14 loops • Beam-centering control • 2 arms  (pit, yaw) = 4 loops Raab: Status of GW Detectors, Especially LIGO

  26. Suspended Mirror Approximates a Free Mass Above Resonance Blue: suspended mirror XF Cyan: free mass XF Data taken using shadow sensors & voice coil actuators Raab: Status of GW Detectors, Especially LIGO

  27. Background Forces in GW Band = Thermal Noise ~ kBT/mode xrms  10-11 m f < 1 Hz xrms  210-17 m f ~ 350 Hz xrms  510-16 m f  10 kHz Strategy: Compress energy into narrow resonance outside band of interest  require high mechanical Q, low friction Raab: Status of GW Detectors, Especially LIGO

  28. Pre-stabilized laser delivers light to the long mode cleaner Start with high-quality, custom-built Nd:YAG laser Improve frequency, amplitude and spatial purity of beam Actuator inputs provide for further laser stabilization Wideband Tidal IO Frequency Stabilization of the Light Employs Three Stages 4 km 15m 10-Watt Laser Interferometer PSL Raab: Status of GW Detectors, Especially LIGO

  29. Pre-stabilized Laser (PSL) Custom-built 10 W Nd:YAG Laser, joint development with Lightwave Electronics (now commercial product) Cavity for defining beam geometry, joint development with Stanford Frequency reference cavity (inside oven) Raab: Status of GW Detectors, Especially LIGO

  30. Digital Interferometer Sensing & Control System Raab: Status of GW Detectors, Especially LIGO

  31. Digital Controls screen example Digital calibration input Analog In Analog Out Raab: Status of GW Detectors, Especially LIGO

  32. Nuclear diameter, 10-15 meter Why is Locking Difficult? One meter Human hair, about 100 microns Earthtides, about 100 microns Wavelength of light, about 1 micron Microseismic motion, about 1 micron Atomic diameter, 10-10 meter Precision required to lock, about 10-10 meter LIGO sensitivity, 10-18 meter Raab: Status of GW Detectors, Especially LIGO

  33. Tidal Compensation Data Tidal evaluation on 21-hour locked section of S1 data Predicted tides Feedforward Feedback Residual signal on voice coils Residual signal on laser Raab: Status of GW Detectors, Especially LIGO

  34. Microseism Microseism at 0.12 Hz dominates ground velocity Trended data (courtesy of Gladstone High School) shows large variability of microseism, on several-day- and annual- cycles Reduction by feed-forward derived from seismometers Raab: Status of GW Detectors, Especially LIGO

  35. LIGO Science Run S1 • 17 days in Aug-Sep 2002 • 3 LIGO interferometers in coincidence with GEO600 and ~2 days with TAMA300 • Joint analyses with GEO reported at Spring APS meeting, papers appearing soon in Phys. Rev. D • Remember: All performance data for all detectors are snapshots that reflect work in progress, not ultimate detector capability. Raab: Status of GW Detectors, Especially LIGO

  36. Thermal Noise Observed in 1st Violins on H2, L1 During S1 ~ 20 millifermi RMS for each free wire segment Raab: Status of GW Detectors, Especially LIGO

  37. Binary Neutron Stars:S1 Range Raab: Status of GW Detectors, Especially LIGO Image: R. Powell

  38. LIGO Science Run S2 • Feb 14 – Apr 14, 2003 • 3 LIGO interferometers in coincidence with TAMA300; GEO600 not available for science running Raab: Status of GW Detectors, Especially LIGO

  39. Binary Neutron Stars:S2 Range S1 Range Raab: Status of GW Detectors, Especially LIGO Image: R. Powell

  40. LIGO Science Run S3 • Oct 31, 2003 – Jan 9, 2004 • 3 LIGO interferometers in coincidence with periods of operation of TAMA300, GEO600 and Auriga Raab: Status of GW Detectors, Especially LIGO

  41. Raab: Status of GW Detectors, Especially LIGO

  42. Binary Neutron Stars:Initial LIGO Target Range S2 Range Raab: Status of GW Detectors, Especially LIGO Image: R. Powell

  43. Future Plans for Terrestrial Detectors • Improve reach of initial LIGO to run 1 yr at design sensitivity • Virgo has made steady progress commissioning components in vertex, now commissioning long arms and due to come on line in ~ 1 year • GEO600, TAMA300, striving for design sensitivity • IGEC expects to network with interferometers for future runs • Advanced LIGO technology under development with intent to install by 2009 Raab: Status of GW Detectors, Especially LIGO

  44. Open up wider band What’s next? Advanced LIGO… Major technological differences between LIGO and Advanced LIGO 40kg Quadruple pendulum Sapphire optics Silica suspension fibers Initial Interferometers Active vibration isolation systems Reshape Noise Advanced Interferometers High power laser (180W) Raab: Status of GW Detectors, Especially LIGO Advanced interferometry Signal recycling

  45. Binary Neutron Stars:AdLIGO Range LIGO Range Raab: Status of GW Detectors, Especially LIGO Image: R. Powell

  46. …and opening a new channel with a detector in space. Planning underway for space-based detector, LISA, to open up a lower frequency band ~ 2011-ish Raab: Status of GW Detectors, Especially LIGO

  47. Summary • We are currently experiencing a rapid advance in the sensitivity of searches for gravitational waves • Elements of world-wide networks of interferometers and bars have been exercised • The near future will see the confrontation of theory with many fine observational results Raab: Status of GW Detectors, Especially LIGO

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