LIGO The Bumpy Road from Construction to Science
LIGO The Bumpy Road from Construction to Science Barry C Barish Caltech LIGO-G 1602199 14 -August-2018
My Goals today • v 1) Integration and Commissioning – Lessons learned from LIGO experience 2) Introduce AMCL and myself to the LSST community
Gravitational Waves • Ripples of spacetime that 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
Suspended Mass Interferometry ~ ~
LIGO Sites Siting Project Approved 1994
LIGO Construction Began in 1994 Evolution over 22 years to Advanced LIGO
LIGO Infrastructure beam tube
LIGO Interferometer Infrastructure 3 -March-2018 Queen's University Colloquium
LIGO Interferometers Hanford, WA Livingston, LA
Interferometer Noise Limits Seismic Noise test mass (mirror) Quantum Noise Residual gas scattering "Shot" noise LASER Wavelength & amplitude fluctuations Beam splitter photodiode Radiation pressure Thermal (Brownian) Noise
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
Evolution of LIGO Sensitivity
Initial LIGO Performance (Final)
Advanced LIGO GOALS Better seismic isolation LIGO-G 1602199 Better test masses and suspension Higher power laser
How to obtain a x 10 sensitivity improvement? Parameter Initial LIGO Advanced LIGO Input Laser Power 10 W (10 k. W arm) 180 W (>700 k. W arm) 10 kg 40 kg Power-recycled Fabry-Perot arm cavity Michelson Dual-recycled Fabry-Perot arm cavity Michelson (stable recycling EO cavities) Mirror Mass Interferometer Topology Laser M GW Readout Method RF heterodyne DC homodyne Optimal Strain Sensitivity 3 x 10 -23 / r. Hz Tunable, better than 5 x 10 -24 / r. Hz in broadband flow ~ 50 Hz flow ~ 13 Hz Seismic Isolation Performance Mirror Single Pendulum 3 -March-2018 Suspensions Quadruple pendulum
200 W Nd: YAG Laser • 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: 34 cm x 20 cm Round-trip optical loss: 75 ppm max 40 kg Compensation plates: 34 cm x 10 cm BS: 37 cm x 6 cm ITM T = 1. 4%
Test Mass Quadruple Pendulum Suspension Optics Table Interface (Seismic Isolation System) Damping Controls Hierarchical Global Controls Electrostatic Actuation Final elements All Fused silica
Seismic Isolation Passive / Active Multi-Stage Queen's University Colloquium
Subsystem Installation at LIGO Sites 2012 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 Sites 2013 Snapshot Each subsystem integrated and tested
Input Optics: Subsytem Tests –> Integrated Tests 2014 Snapshot
Full Commissioning begins Sept 2014 March 2015
Sensitivity for Advanced LIGO At ~40 Hz, Factor ~100 improvement Broadband, Factor ~3 improvement Initial LIGO O 1 a. LIGO Design a. LIGO
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)
Observed Signals Sept 14, 2015 hg– 14, September 2015 Queen's University Colloquium
Gravitational Wave Event GW 150914 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) Queen's University Colloquium. Phys. Rev. Lett. 116, 061102 (2016)
• Hardware – – Construction to Science 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
Thanks!
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