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Innovative Technologies for the Gravitational-Wave Detectors LIGO and Virgo
Jan Harms

INFN, Sezione di Firenze On behalf of LIGO and Virgo
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Global Network of Detectors
LIGO GEO

VIRGO
KAGRA

LIGO

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Commissioning of the LIGO Detector
NS/NS Inspiral range
S1 ~ 100 kpc S2 ~ 0.9Mpc S3 ~ 3 Mpc

S4 ~ 8 Mpc
S5 ~ 15 Mpc

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Instrumental Noise
Seismic Suspension thermal Terrestrial gravity

Quantum noise Terrestrial gravity Suspension thermal Quantum noise
Quantum noise Coating thermal

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New Technology for the Advanced Detectors

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Seismic Isolation for Advanced LIGO
Suspension system Internal seismic isolation
Matichard et al., MIT

4 stages

Rowan et al., Glasgow Robertson et al., Caltech
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Optics and Suspension Improvements (aVirgo and aLIGO)
Substrates (SiO2) · Main goal: minimize light scattering · Polishing quality: about 0.1nm rms · RoC errors around 0.1% Coatings (SiO2,Ta2O5) · Main goals: minimize scattering and thermal noise · Can be produced without significantly deteriorating mirror profile · High purity, few point defects Suspensions (SiO2) · Main goal: minimize thermal noise · Monolithic implementation · Diameter: 0.4mm
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Thermal Compensation
Laser Ring heater Reduced deformation

Ring heaters aVirgo aLIGO

V.Malvezzi, Rome A.Brooks, Caltech
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Feed-Forward Noise Cancellation
Ground motion shakes mirrors, and therefore cavity length changes.

No improvement below some frequency since sensor SNR is insufficient to resolve small differential ground motion.
Rev.Sci.Instr. 83, 024501, 2012
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Beyond Advanced: Quantum Noise Reduction

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Quantum Noise
Squeezing and filter cavities can be used to reduce quantum noise at all frequencies.
Filter cavity

Quantum noise of laser does not limit detector sensitivity.

squeezing out squeezing in

Photon statistics at output port are mainly determined by vacuum fields incident at output port.
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Counting photons
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Improving Quantum-Noise Reduction
Quantum-noise reduction by squeezing has been first demonstrated in large-scale detectors at GEO600.
Since then, scientists at GEO600 have been trying to improve the performance by characterizing and minimizing optical loss.

A. Khalaidovski, GEO600
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K. Dooley, GEO600 (2012)
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Squeezing at LIGO Hanford
Nature Photonics, 177 (2013)

Strain sensitivity [Hz-1/2]

10-22

Squeezing applied to LIGO interferometer led to best sensitivity for a gravitational-wave detector to date!

10-23 100 1000

Frequency [Hz]
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Beyond Advanced: Cryogenics

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How to Make GW Detectors Cryogenic?
New Laser wavelength:1560nm Adjusted suspension design New material for optics and suspensions: Si

Cryogenic infrastructure

Shapiro, Stanford
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Decreasing Thermal Noise
Decreasing thermal noise efficiently is an optimization problem that includes the cooling process.

Smith, Caltech, 2013
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Materials at Cryogenic Temperatures
Mechanical loss measurements on silicon wafers
Mechanical loss of crystalline coatings is significantly better than in amorphous coatings

Prohorov and Mitrofanov, MSU, 2013
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Cole et al, Vienna, 2013
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Beyond Advanced: Terrestrial Gravity Noise

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Terrestrial Gravity Noise
Anthropogenic noise Ocean waves

Rivers

Wind and atmosphere To understand Newtonian noise, you need to understand the sources and propagation effects.

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Newtonian Noise at LIGO
Estimated NN Budget
10-20

· Seismic surface waves · Vibrations of buildings · Vibrations of water pipes · Vibrating vacuum chambers · Exhaust fans · Sound inside and outside buildings
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Strain sensitivity [Hz-1/2]

10-21

10-22
10-23 10-24 10-25 1

Frequency [Hz]
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Phys. Rev. D 86, 102001 (2012)
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Gravity Noise Cancellation

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Seismic Underground Array
· Stations equipped with broadband seismometers (T240, STS-2) · Infrasound microphones installed at almost all stations. · Stations at depths between 90m and 1250m

x x x

4100ft level

Microphone

Seismometer

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Closing the Circle
Davis chamber, 2009 Outside

Inside

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