Institute for Gravitational Research

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

3
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

4
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

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

7
GEO 600
8
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

mirror
beamsplitter
laser and injection optics
mirror
detector

• 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

• 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 - J19392134
• h0 lt 10-20

13
From initial to Advanced LIGO

• 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)

Kip S. Thorne California Institute of
Technology used with permission
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
  RD programme being coordinated by the LIGO
  Scientific Collaboration working with the LIGO
  laboratory

LIGO Hanford

• 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

15
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

17
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