Status of the Laser Interferometer Gravitational-Wave Observatory

1. Status of the Laser Interferometer Gravitational-Wave Observatory Reported on behalf of LIGO colleagues by Fred Raab, LIGO Hanford Observatory

2. Laser Interferometer Gravitational-wave Observatory LIGO Mission: To sense the distortions of spacetime, known as gravitational waves, created by cosmic cataclysms and to exploit this new sense for astrophysical studies Over nearly 400 years, astronomy has developed many clever ways to “see” and study the universe; LIGO hopes to add a “sound track” using interferometers that function like large terrestrial microphones, listening for vibrations of space. Status of LIGO

3. Gravitational Collapse and Its Outcomes Present LIGO Opportunities fGW > few Hz accessible from earth fGW < several kHz interesting for compact objects Status of LIGO

4. Potential LIGO Sources • Supernovae, with strength depending on asymmetry of collapse • Inspirals and mergers of compact stars, like black holes, neutron stars • Starquakes and wobbles of neutron stars and black holes • Stochastic waves from the early universe, cosmic strings, etc. • Unknown phenomena Status of LIGO

5. Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy Rendering of space stirred by two orbiting black holes: Gravitational Waves Status of LIGO

6. Catching WavesFrom Black Holes Sketches courtesy of Kip Thorne Status of LIGO

7. In 1974, J. Taylor and R. Hulse discovered a pulsar orbiting a companion neutron star. This “binary pulsar” provides some of the best tests of General Relativity. Theory predicts the orbital period of 8 hours should change as energy is carried away by gravitational waves. Taylor and Hulse were awarded the 1993 Nobel Prize for Physics for this work. Energy Loss Caused By Gravitational Radiation Confirmed Status of LIGO

8. How does LIGO detect spacetime vibrations?

9. Important Signature of Gravitational Waves Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction. Status of LIGO

10. End Mirror End Mirror Beam Splitter Laser Screen Sketch of a Michelson Interferometer Viewing Status of LIGO

11. The Laser Interferometer Gravitational-Wave Observatory LIGO (Washington) LIGO (Louisiana) Supported by the U.S. National Science Foundation; operated by Caltech and MIT; the research focus for more than 400 LIGO Scientific Collaboration members worldwide. Status of LIGO

12. Observatories at Hanford, WA (LHO) & Livingston, LA (LLO) Support Facilities @ Caltech & MIT campuses The Four Corners of the LIGO Laboratory LHO LLO Status of LIGO

13. Part of Future International Detector Network Simultaneously detect signal (within msec) Virgo GEO LIGO TAMA detection confidence locate the sources decompose the polarization of gravitational waves AIGO Status of LIGO

14. Spacetime is Stiff! => Wave can carry huge energy with miniscule amplitude! h ~ (G/c4) (ENS/r) Status of LIGO

15. Some of the Technical Challenges • Typical Strains less than ~ 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 • Engineer structures to mitigate recoil from atomic vibrations in suspended mirrors • Provide clear optical paths within 4-km UHV beam lines Status of LIGO

16. Fabry-Perot-Michelson with Power Recycling 4 km or Optical Cavity 2-1/2 miles Beam Splitter Recycling Mirror Photodetector Laser Status of LIGO

17. Vacuum Chambers Provide Quiet Homes for Mirrors View inside Corner Station P < 10-6 Torr in chambers to reduce acoustics & molecular Brownian motion Standing at vertex beam splitter Status of LIGO

18. Beam Tube Provides Distortion-Free 4-km Pathway for Light • Requires P ~ 10-9 Torr H2 Equivalent • Baked out by insulating tube and driving ~2000 amps from end to end Status of LIGO

19. 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 Status of LIGO

20. Design for Low Background Spec’d From Prototype Operation For Example: Noise-Equivalent Displacement of 40-meter Interferometer (ca1994) Status of 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 Status of LIGO

22. damped springcross section Seismic Isolation – Springs and Masses Status of 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 Status of LIGO

24. Core Optics Suspension and Control Optics suspended as simple pendulums Local sensors/actuators provide damping and control forces Mirror is balanced on 1/100th inch diameter wire to 1/100th degree of arc Status of LIGO

25. Suspended Mirror Approximates a Free Mass Above Resonance Status of LIGO

26. 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 Status of LIGO

27. Interferometer Control System • Multiple Input / Multiple Output • Three tightly coupled cavities • Ill-conditioned (off-diagonal) plant matrix • Highly nonlinear response over most of phase space • Transition to stable, linear regime takes plant through singularity • Employs adaptive control system that evaluates plant evolution and reconfigures feedback paths and gains during lock acquisition • But it works! Status of LIGO

28. Composite Video Steps to Locking an Interferometer Y Arm Laser X Arm signal Status of LIGO

29. Watching the Interferometer Lock Y Arm Laser X Arm signal Status of LIGO

30. Nuclear diameter, 10-15 meter Why is Locking Difficult? One meter, about 40 inches 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 Status of LIGO

31. 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 Status of LIGO

32. 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 Status of LIGO

33. 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 Status of LIGO

34. Thermal Noise Checked in 1st Violins on H2, L1 During S1 Almost good enough for tracking calibration. Status of LIGO

35. Chronology of Detector Installation & Commissioning • 7/98 Begin detector installation • 6/99 Lock first mode cleaner • 11/99 Laser spot on first end mirror • 12/99 First lock of a 2-km Fabry-Perot arm • 4/00 Engineering Run 1 (E1) • 10/00 Recombined LHO-2km interferometer in E2 run • 10/00 First lock of LHO-2km power-recycled interferometer • 2/01 Nisqually earthquake damages LHO interferometers • 4/01 Recombined 4-km interferometer at LLO • 5/01 Earthquake repairs completed at LHO • 6/01 Last LIGO-1 mirror installed • 12/01 Power recycling achieved for LLO-4km • 1/02 E7: First triple coincidence run; first on-site data analysis • 1/02 Power recycling achieved for LHO-4km • 9/02 First Science Run (S1) completed • 2/03 Second Science Run (S2) begun Status of LIGO

36. LIGO Sensitivity Livingston 4km Interferometer May 01 Jan 03 Status of LIGO

37. S1 Analysis Working Groups • Data from S1 is being analyzed by LSC working groups for: • Detector Characterization – monitors of data quality, instrument diagnostics, tuning displays • Binary Inspirals – modeled chirps from BH’s, NS’s, MACHO’s • Bursts – unmodeled deviations from stationarity; independent searches; searches triggered on GRB’s, SN’s • Periodic Sources – known pulsar search; work toward all-sky search for unknown pulsars • Stochastic Background – early universe Status of LIGO

38. Summary • First triple coincidence run completed (17 days with ~23% triple coincidence duty factor) • On-line data analysis systems (Beowulf parallel supercomputer) functional at LHO and LLO • S1 coincidence analyses with GEO & TAMA are first science analyses with international laser-GW network • First science data analysis ongoing • Interferometer control system still being commissioned and tuned • Working to increase immunity to high seismic noise periods (especially important at LLO) • S2 running 14Feb03 – 14Apr03 Status of LIGO

39. Future Plans • Improve reach of initial LIGO to run 1 yr at design sensitivity • Advanced LIGO technology under development with intent to install by 2008 • Planning underway for space-based detector, LISA, to open up a lower frequency band ~ 2015 Status of LIGO

40. Despite a few difficulties, science runs started in 2002. Status of LIGO