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1
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)
2
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
2
h
L
L
5
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
6
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
9
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
10
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
11
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
12
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
13
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)
14
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
16
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