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. Gravity gradient wall ADVANCED GROUND - BASED DETECTORS 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” massesusing 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. 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 - J1939+2134 h0 < 10-20 Strain sensitivity of GEO interferometer GEO and LIGO begin to work!

13. 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) Initial interferometers hrms = h(f) f ~10 h(f) 15 in h ~3000 in rate Open up wider band Reshape noise Advanced interferometers From initial to Advanced LIGO Kip S. Thorne California Institute of Technology used with permission

14. 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 Glasgow rôle in Advanced LIGO 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