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Institute for Gravitational Research

Director: Jim Hough + 4 Academic Staff

(Norna Robertson, Harry Ward, Ken Strain, Geppo Cagnoli) + Joint academic staff member with Astronomy Group (Graham

Woan) + 8 Research Assistants / Hon Research Fellow + 6 Postgraduate Research Students (1 joint with Astronomy Group) + 7 Technical, Engineering and Research Associate support staff + Secretary

Aim:

To observe gravitational waves using laser interferometric

techniques on earth (GEO 600, Advanced LIGO, EURO), and in space (LISA)

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Gravitational waves

Propagating ripples in the curvature of spacetime causing time-varying strains in space

Produced in the form of Bursts

Compact binary coalescences: NS/NS, NS/BH, BH/BH Stellar collapse (asymmetric) to NS or BH  Black hole interactions

Continuous waves Pulsars Binary orbits long before coalescence Low mass X-ray binaries (e.g. SCO X1) Modes and Instabilities of neutron stars 

Stochastic background Interactions in the early Universe

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The gravitational waves spectrum

As in the electromagnetic case, gravitational wave signals cover a wide range of frequencies. Ground-based detectors are noise-limited to operation above ~10 Hz ; space-based detectors are required for lower frequency observations

Gravity gradient wall

ADVANCED GROUND - BASED DETECTORS

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Effect of a gravitational wave

Modulation of the proper distance between free test particles

A gravitational wave of amplitude h, will produce a strain

between masses a distance L apart

Detection conveniently done by monitoring the distance between

“free” masses using laser interferometry to measure the fluctuations

in relative length of two approximately orthogonal arms formed

between suitably “isolated” mirrors

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h

L

L

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Detectability ?

The 1st generation detectors under construction are optimised for the

“audio band” – above 10Hz

These may well make the first detections

Plans for 2nd generation interferometers (2006?) are well advanced, and

plans for 3rd generation detectors (2010?) are now being considered

Each generation is planned to have improved by 10 in amplitude, 100 in

energy and 1000 in volume of space searched

These should make frequent detections

LISA is being developed for a launch around 2011 as a joint ESA-NASA

mission

LISA will open the low-frequency window (below 1Hz), where it must make

many detections, some of which will be at very high signal-to-noise ratios

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Interferometrically sensed gravitational wave detectors

5 detector systems approved / now being developed worldwide:

LIGO (USA) 2 detectors of 4km arm length + 1 detector of 2km

arm length Washington State and Louisiana

VIRGO (Italy/France) 1 detector of 3km arm length Cascina, near

Pisa

GEO 600 (UK/Germany) 1 detector of 600m arm length

Hannover

TAMA 300 (Japan) 1 detector of 300m arm length Tokyo

LISA Spaceborne detector of 5 x 106 km arm length

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GEO 600

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GEO 600

Initial GEO 600 strategy: to build a low cost detector of comparable sensitivity to the

initial LIGO and VIRGO detectors to take part in gravitational wave searches in coincidence with

these systems

Unique GEO 600 design technology to make this possible:

Advanced suspension technology for low thermal noise

Advanced optics configuration – signal recycling

Disadvantage: for geographical reasons the GEO armlength (600m) cannot be

extended to the 3/4kms of VIRGO/LIGO

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Monolithic silica suspensions

GEO600 is the first interferometer to use such suspensions to reduce thermal noise

The technology offers ~10 x lower noise than the alternative designs that are used in the other initial interferometers

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Advanced interferometry

One of the fundamental limits to interferometer sensitivity is photon shot noise

Power recycling effectively increases the laser power

Signal recycling – a Glasgow invention – trades bandwidth for improved sensitivity

detector

mirror

laser and injection

optics

beamsplitter

mirror

With signal recycling the frequency and bandwidth of the optimum sensitivity are easily adjustable

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Timescales first detectors

GEO and LIGO Main interferometer under development during 2001 / 2002 First coincident run took place over New Year 2002 Further runs planned for summer and autumn 2002 Data exchange with LIGO agreed : GEO is a member of the

LIGO I Consortium based on data exchange

TAMA some data taking for periods over past year and coincidence

with LIGO and GEO soon

VIRGO First operation scheduled for 2003 Data exchange agreement being discussed

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GEO and LIGO begin to work!

Preliminary snapshots of GEO and LIGO noise spectra

As expected, the initial performance of GEO and of LIGO is still some way from their design sensitivities, but noise studies and improvements are progressing well

Strain sensitivity of GEO interferometer

GEO not yet configured with final optics and signal recycling still to be installed

Preliminary result from Glasgow analysis of GEO data: upper limit for GW from PSR - J1939+2134

h0 < 10-20

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From initial to Advanced LIGO

Kip S. Thorne

California Institute of Technology

used with permission

Initial interferometers

Advanced interferometers

Open up wider band

Reshape noise

15 in h ~3000 in

rate

hrms = h(f) f ~10 h(f) Signal recycling is added to

upgrade the interferometer

configuration

GEO 600 style silica

suspension technology and

multiple stage pendulums

replace the current wire-

loop single stage

suspensions

Sapphire optics are

proposed for low thermal

noise (small mechanical

dissipation) and high optical

power handling (high ratio

of conductivity to dn/dT)

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The Glasgow rôle in Advanced LIGO

Technologies under development in GEO are essential ingredients of Advanced LIGO

In recognition of this, LIGO have offered GEO partnership in Advanced LIGO for a very modest financial contribution

Glasgow is undertaking key elements of the enabling research for Advanced LIGO, with the IGR R&D programme being coordinated by the LIGO Scientific Collaboration working with the LIGO laboratory

The IGR: was invited to undertake an experimental investigation of signal recycling

applied to suspended-optics interferometers (based in our new JIF-funded laboratory)

is centrally involved in the development of GEO fused-silica suspension technology for application in Advanced LIGO

cooperates in the investigations into mechanical losses in fused-silica and sapphire mirrors for use in Advanced LIGO

LIGO Hanford

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Preparing for post-Advanced LIGO

The IGR plans research in materials/Thermal Noise research for future detectors – e.g. Euro

silicon at low temperature direct measurement of thermal noise in samples with

inhomogeneous loss

novel interferometry

new signal recycling interferometer topologies all reflective interferometer systems

… and is also engaged on ESA TRP-funded contracts on optical bench design and construction for SMART 2 phase readout systems for LISA

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Timescales

Advanced LIGO 2003-2009 £6M Suspensions developed from GEO Interferometry developed from GEO

GEO upgrade 2006-2009 £4M Silicon test masses at low temperature All reflective interferometry

EURO development 2008 onwards £12M+ Long baseline, based on GEO upgrade?

SMART 2 and LISA 2006/2011 £12M+ Optical design and construction

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Conclusion

The IGR has a clear 15 year strategy for the initiation and development of the field of gravitational wave astronomy

GEO proves advanced technology and takes part in initial gw searches

The contribution of GEO technology buys the UK a pivotal position in the development and use of Advanced LIGO

Glasgow expertise in high precision interferometry and in ultra-stable optical construction techniques ensures a prominent rôle in the space gravitational wave detector, LISA, and in its precursor demonstrator mission, SMART 2

The evolution of GEO to an upgraded system allows proving of emerging technologies and materials

An upgraded GEO places the UK in a compelling position to play a lead rôle in a large scale European detector in the post-Advanced LIGO era