Nergis Mavalvala MIT IAU214, August 2002 Status of LIGO Laser Interferometer Gravitational-wave Observatory Hanford, WA Livingston, LA Nergis Mavalvala MIT IAU214, August 2002

Gravitational wave Interferometers: the principle General Relativity (Einstein 1916) predicts freely propagating transverse space-time distortions h ~ 10-21 DL = h L Pirani ‘56, Gerstenshtein and Pustovoit, Weber, Weiss ’72 Michelson Interferometer IAU214 - August 2002

Why an Observatory? Two sites Long lifetime First detector (LIGO I) Three interferometers Coincidence Long lifetime Facilities limits First detector (LIGO I) Now This talk Advanced detectors (LIGO II and beyond) 2006++ Initial Advanced IAU214 - August 2002

Past…Future 1996 Construction underway (mostly civil) 1997 Facilities Construction (vacuum system) 1998 Interferometer Construction (facilities completed) 1999 Construction Completed (interferometers installed in vacuum) 2000 Detector Installation (commissioning subsystems) 2001 Commission Interferometers (first coincidences) 2002 Sensitivity Studies (initial LIGO I Science Run) 2003+ LIGO I Data Run (one year integrated data at h ~ 10-21) 2006++ Begin advanced LIGO installation IAU214 - August 2002

Initial LIGO Sensitivity Goal Strain sensitivity < 3x10-23 1/Hz1/2 at 200 Hz Displacement Noise Seismic motion Thermal Noise Radiation Pressure Sensing Noise Photon Shot Noise Residual Gas Facilities limits much lower IAU214 - August 2002

Detector Overview Vacuum 20 kW 10 W Laser 4 km 300 W Input Optics IAU214 - August 2002

Seismic Isolation Seismic isolation stacks Stainless steel masses  600 kg each stage Helicoil springs with lossy viscoelastic layer  Q ~ 40 3 to 4 stages  10-6 to 10-8 for f > 10 Hz IAU214 - August 2002

Core Optics 25 cm diameter, 10 kg fused silica optics Polished substrates Micro-roughness  < 10 ppm scatter Optical coatings < 2 ppm scatter < 1 ppm absorption Metrology  Surface uniformity ~1 nm rms IAU214 - August 2002

Suspensions Single wire loop suspensions Four electromagnetic actuators Four ‘shadow’ sensors for local position sensing Small optic Large optic IAU214 - August 2002

Optical Design of the Interferometers Requires test masses to be held in position to 10-10-10-13 meter: “Locking the interferometer” Light bounces in arm cavities ~130 times a increased phase sensitivity Light is “recycled” ~30 to 50 times Input Optics Laser Dark fringe signal IAU214 - August 2002

Interferometer Sensing and Control Pre-Mode Cleaner Laser IAU214 - August 2002

Engineering Run 7 (E7): LIGO + GEO + ALLEGRO IAU214 - August 2002

Strain Sensitivity during E7 IAU214 - August 2002

Evolution of strain sensitivity Major improvements Front-end electronics (ADC) noise  whiten signal Laser frequency noise  common-mode servo Output electronics (DAC) noise  whiten signal Sensing electronics noise  increase light level IAU214 - August 2002

LIGO I Status Summary: What works All three interferometers locked for hours at a time in power-recycled configuration a Grec ~ 15 – 45 Lock acquisition is done using sys id methods a MTTL ~ 1 – 2 minute Optical parameters consistent with lab metrology a mirror losses < 70 ppm Tidal feedback systems operational a range of 200 mm pk-pk Mechanical (internal) modes of test masses excited a 104 < Q < 107 Laser input power 1 – 5 W but all light power not detected (PD saturations) Coupling to environment, e.g. Aircrafts flying by can be seen (heard?) Earthquakes Trains twice a day at Livingston Anthropogenic noise IAU214 - August 2002

LIGO I Status Summary: What doesn’t (yet) Seismic pre-isolation system At LLO 10x reduction in rms displacement of optics desired Active sensing and piezoelectric actuation system installed Hydraulic actuation prototyping underway for installation in 2003 Digital controls for optics suspension systems Greater flexibility for tuning servos Easier to orthogonalize displacement and angles of optic Installed/tested on Hanford 4km L4k, e.g., limited by coil driver noise at low frequencies Alignment control systems Partially operational (feedback loops closed on 2 – 4 of 12 degrees of freedom) Necessary to reduce spurious signals at AS port that causes photodiode saturations Increase detected light levels  overcome sensing noise at high frequencies Electronics improvements New system layout being designed (EMI/RFI mitigation) Lower noise A/D converters IAU214 - August 2002

The Task Ahead Engineering runs Science runs Characterize and improve detector sensitivity and reliability Exercise data analysis system end-to-end pipeline Science runs Upper limits (E7 and beyond) Scientific searches (S1 begins 08/23/02) Commissioning remaining subsystems Factor of 100 (above 400 Hz) to 100000 (at 40 Hz) improvement needed to reach design sensitivity LIGO II R&D already underway IAU214 - August 2002

Detection Strategy: Coincidences Two sites – three interferometers Single interferometer  50/hr (non-gaussian level) Hanford 4km + 2km  1/day (correlated rate) Hanford + Livingston  0.1/yr (uncorrelated) Data recording (time series) Gravitational wave signal = 0.2 MB/sec Total data = 16 MB/sec On-line filters, diagnostics, data compression Off-line data analysis, archiving… Signal extraction Signal from noise (vetoes, noise analysis) Templates, wavelets… IAU214 - August 2002