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Explore the journey from LIGO construction to scientific discoveries, highlighting seismic, thermal, and quantum noise challenges and advanced technologies enhancing sensitivity. Witness the evolution of LIGO's infrastructure, interferometer limits, test masses, and subsystem integrations.
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LIGOThe Bumpy Road from Construction to Science Barry C Barish Caltech 14-August-2018
My Goalstoday • v 1) Integration and Commissioning – Lessons learned from LIGO experience 2) Introduce AMCL and myself to the LSST community
Gravitational Waves • Ripples of spacetimethat stretch and compress spacetime itself • The amplitude of the wave is h ≈ 10-21 • Change the distance between masses that are free to move by ΔL = h x L • Spacetime is “stiff” so changes in distance are very small L ΔL
Siting LIGO LIGO Sites Project Approved 1994
LIGO Construction Began in 1994 Evolution over 22 years to Advanced LIGO
LIGOLIGO Infrastructure beam tube
LIGO Interferometer Infrastructure Queen's University Colloquium
Hanford, WA LIGO Interferometers Livingston, LA
Seismic Noise Quantum Noise Radiation pressure Residual gas scattering "Shot" noise Wavelength & amplitude fluctuations Thermal (Brownian) Noise Interferometer Noise Limits test mass (mirror) LASER Beam splitter photodiode
What Limits LIGO Sensitivity? • Seismic noise limits low frequencies • Thermal Noise limits middle frequencies • Quantum nature of light (Shot Noise) limits high frequencies • Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals Queen's University Colloquium
Advanced LIGO GOALS Better seismic isolation Higher power laser Better test masses and suspension
200W Nd:YAGLaser • Stabilized in power and frequency • Uses a monolithic master oscillator followed by injection-locked rod amplifier
Mirror / Test Masses • Mechanical requirements: bulk and coating thermal noise, high resonant frequency • Optical requirements: figure, scatter, homogeneity, bulk and coating absorption 40 kg Test Masses: 34cm x 20cm Round-trip optical loss: 75 ppm max 40 kg Compensation plates: 34cm x 10cm BS: 37cm x 6cm ITM T = 1.4%
Optics Table Interface (Seismic Isolation System) Damping Controls Hierarchical Global Controls Electrostatic Actuation Test Mass Quadruple Pendulum Suspension Final elements All Fused silica
Seismic IsolationPassive / Active Multi-Stage Queen's University Colloquium
Subsystem Installation at LIGO Sites2012 Snapshot Each subsystem installation led by subsystem leader and on-site subsystem manager, plus coordination with system engineering and commissioning teams
Subsystem Integration at LIGO Sites2013 Snapshot Each subsystem integrated and tested
Input Optics: Subsytem Tests –> Integrated Tests2014 Snapshot
Full Commissioning begins Sept 2014Sept 2014 March 2015
Sensitivity for Advanced LIGO Broadband, Factor ~3 improvement At ~40 Hz, Factor ~100 improvement Initial LIGO O1 aLIGO Design aLIGO
Finding a weak signal in noise • “Matched filtering” lets us find a weak signal submerged in noise. • For calculated signal waveforms, multiply the waveform by the data • Find signal from cumulative signal/noise PHYS. REV. X 6,041015 (2016)
hg Observed Signals – Sept 14, 2015 September 14, 2015 Queen's University Colloquium
Gravitational Wave EventGW150914 Data bandpass filtered between 35 Hz and 350 Hz Time difference 6.9 ms with Livingston first Second row – calculated GW strain using Numerical Relativity Waveforms for quoted parameters compared to reconstructed waveforms (Shaded) Third Row –residuals bottom row – time frequency plot showing frequency increases with time (chirp) Phys. Rev. Lett. 116, 061102 (2016) Queen's University Colloquium
Construction to Science • Hardware • Equipment construction and Intallation; • Integration into subsystems; • Commissioning subsystems; • Overall Commissioning • Data Handling • Data Quality (glitches, etc) • Calibrations (sensitivity, etc) • Data Pipelines (unmodeled, templates, etc) • Data Analysis • Numerical Relativity • Parameter Estimation