Overview of Advanced LIGO

March 2011

Rencontres de Moriond

Sheila RowanFor the LIGO Scientific

Collaboration

The Global Network of Gravitational Wave Detectors

GEO600Germany

VIRGOItaly

LIGO

LIGO

TAMAJapan

LIGO sites (US)

LIGO Livingston Observatory• 1 interferometer

• 4 km arms

• 2 interferometers• 4 km, 2 km arms

LIGO Hanford Observatory

LIGO Observatories are operated by Caltech and MIT

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The LIGO Scientific Collaboration (LSC)

• The LSC carries out the scientific program of LIGO – instrument science, data analysis.

• The 3 LIGO interferometers and the GEO600 instrument are analyzed as one data set(also share our data with French-Italian Virgo)

• Approximately 800 members

• ~ 50 institutions including the LIGO Laboratory

• Participation from (at least) Australia, Germany, India, China, Korea, Italy, Hungary Japan, Russia, Spain, the U.K. and the U.S.A.

Timeline of GW searches to 2011

We are here

Data analysis ongoing

1989

LIGO Proposal submitted to NSF

1995

Construction started

1999

Inauguration

Advanced LIGO construction funded

The worldwide GW roadmap for the future

We are here

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Advanced LIGO

Factor of 10 greater sensitivity than initial LIGO

Factor 4 lower start to sensitive frequency range» ~10 Hz instead of ~40 Hz» More massive astrophysical systems,

greater reach, longer observation of inspirals

Intended to start gravitational-wave astronomy

Frequent detections expected – exact rates to be determined, of course» Most likely rate for NS-NS inspirals

observed: ~40/year

100 million

light years

Advanced LIGO

Enhanced LIGO Initial LIGO

(See J. Abadie et al “Predictions for the Rates of Compact Binary Coalescences Observable by Ground-based Gravitational-wave Detectors”,arXiv:1003.2480; submitted to CQG)

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Advanced LIGO Scope

Re-use of vacuum system, buildings, technical infrastructure

Replacement of virtually all initial LIGO detector components» Re-use of a small quantity of

components where possible

Three interferometers, as for Initial LIGO All three interferometers 4km in length

» For initial LIGO, one of the two instruments at Hanford is 2km

Advanced LIGO – path to improved sensitivity

Advanced LIG

O

(See Roman Schnabel’s talk on thoughts on how to improve on quantum

noise limited sensitivities..)

Design Outline

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Recombined Fabry-Perot Michelson with Signal recycling (increase sensitivity,

add tunability) Active seismic isolation, quadruple

pendulum suspensions (seismic noise wall moves from 40Hz 10 Hz)

Fused Silica Suspension(decreased low-frequency thermal noise)

40 kg test masses (lower photon pressure noise)

Larger test mass surfaces, low-mechanical-loss optical coatings (decreased mid-band thermal noise)

~20x higher input power (lower shot noise)

Laser

Test Masses MArms of length LCavity finesse F

INITIAL LIGO LAYOUT

Power recycling mirror to increase circulating power

Michelson for sensing strain

Fabry-Perot arms to increase interaction time

GW signal

Signal Recycling Mirror to tune response

ADVANCED

aLIGO – seismic Isolation – outside and inside the tanks

aLIGO Suspension Systems – What They Need to Do

Support the optics to minimise the effects of» seismic noise acting at the support point» thermal noise in the suspension

Test mass noise requirement: 10-19 m/√Hz at 10 Hz

Provide damping of low frequency suspension resonances (local control), and

Provide means to maintain interferometer arm lengths (global control)» while not compromising low thermal noise of mirror» and not introducing noise through control loops

Provide interface with seismic isolation system and core optics system Support optic so that it is constrained against damage from earthquakes

Main suspensions

40kg fused silica mirror suspended on 4 fused silica fibres to give low-thermal-noise suspension ~£8.2M contribution from

GEO UK (Science and Technology Facilities Council)

Prototype fused silica monolithic suspension successfully installed at MIT test facility

(See talk from Angus Bell)

Most test mass suspension components at both observatories are now cleaned, baked, and assembled into sub-assemblies

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40 kg substrates of high optical quality fused silica» Available in suitably large sizes» Low optical absorption at 1064nm» Can be suitably polished and coated » Low mechanical loss

Main mirrors (test masses)

For mirrors with spatially inhomogeneous mechanical loss we should not simply add incoherently the noise from the thermally excited modes of a mirror – loss from a volume close to the laser beam dominates.

The loss of the dielectric multilayer coatings used to form highly reflective mirrors at 1064nm could be expected to be an important parameter

Thermal noise from optical mirror coatings

Current coatings in all detectors are made of alternating layers of ion-beam-sputtered SiO2 (low refractive index) and Ta2O5 (high index)

Experiments suggest: » Thermal noise from mechanical loss of the dielectric mirror coatings will limit

sensitivity of 2nd generation interferometric gravitational wave detectors

Coating thermal noise will limit

sensitivity between ~ 40 and 200 Hz

101

102

103

Frequency (Hz)

10-24

10-23

10-22

Str

ain

(1/

Hz

)

» Ta2O5 is the dominant source of dissipation in current SiO2/Ta2O5 coatings

» Doping the Ta2O5 with TiO2 can reduce the mechanical dissipation

= aLIGO baseline design

(Just one example of impact of experimental GW research on other fields:» Coating noise limits performance of laser stabilisation cavities;

frequency combs; other precision physics expts» Very active research area both for ‘beyond advanced’ GW detectors

and other apps)

Projected Advanced LIGO sensitivity curve

The aLIGO laser

2W 35W 180W 165W

(for more info on high power laser development see talk by Patrick Kwee)

~$14M contribution from GEO Germany (Max Planck Society)

3 complete laser systems, including lasers, servos, reference cavities, etc.

Installation of first article laser at Livingston Observatory has started

aLIGO thermal compensation

• Wavefront sensors for Thermal Compensation System (Adelaide)

• Cavity pre-lock length stabilization system, and ‘tip-tilt’ in-vacuum steering mirrors, for Interferometer Sensing and Control (ANU)

• ~$1.7M from Australian Research Council

‘LIGO-Australia’ (see talk from David Blair)

Goal–

• a southern hemisphere interferometer early in the Advanced LIGO & Advanced Virgo operating era

• Install one of the Advanced LIGO interferometers planned for Hanford into infrastructure in Australia provided by Australia for possible detector operation in 2017

In-principle approval from NSF Australian proposal for

construction funds submitted March 2011

IndIGO is preparing proposal for significant funding to participate in and contribute to LIGO-Australia.

Figure from: LIGO-DOC: T1000251

Status of project to date

Half way done! – excellent progress 20th October 2010 : Handoff of the LIGO Observatories

to the aLIGO project First new parts going in NOW System upgrades staggered Last IFO should realistically be back online in 2015. Tuning and optimizing to reach design sensitivity

Conclusions

Initial LIGO attained its design sensitivity and has produced astronomically important upper limits on gravitational wave production.

Advanced LIGO should increase our sensitivity by more than 10. At that sensitivity, GW detection should be a frequent occurrence.

Advanced LIGO is scheduled to be online by 2015. Collaboration in the worldwide GW community is growing. The LIGO-

Virgo Collaboration (LIGO, GEO, and Virgo) share data, analysis efforts, and technical knowledge.

Exciting (and unexpected?) physics awaits us!

Extra slides follow

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Advanced LIGO: Sensitivity

As for Initial LIGO, we specify the sensitivity of Advanced LIGO by an RMS sensitivity: 10-22 hRMS in a 100 Hz band

» A factor of 10 improvement over Initial LIGO

Flexibility of tuning will allow a range of responses

Anticipated performance is better than above – roughly 3x10-23 hRMS in a 100 Hz band, around 250 Hz, tuned for NS -NS inspirals