1. interferometric detector for GW: status and perspectives Giovanni Losurdo INFN Firenze-Urbino e-mail: losurdo@fi.infn.it

2. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino The ultimate goal GW astronomy: a new window on the universe GW ??

3. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Measure the space-time strain using light Principle of Detection GW acting on a ring of freely falling masses Need to measure:  L ~ 10 -18 m Target h ~ 10 -21 (NS/NS @Virgo Cluster) Big challenge for experimentalists! Interference fringes Feasible L ~ 10 3 m LIGO figures

4. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino P out depends also on P in,  L. ITF sensitive to power and frequency fluctuations, displacement noises, … A simple detector

5. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Power fluctuations limit the phase sensitivity. Ultimate power fluctuations associated to the quantum nature of light Shot noise (assuming P, stable): L = 100 km, P = 1 kW  Lengthen the detector to 100 km. Increase the light power to 1 kW. HOW? Optical Readout Noise

6. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino 100 km ITF? Effective length: Fabry-Perot cavities: amplify the length-to-phase transduction Higher finesse  higher d  dL Drawback: works only at resonance

7. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino 1 kW Power? Interferometer Ecology: recycle the wasted light! P eff = Recycling factor ·P in 20 W  1 Kwatt Shot noise reduced by a factor  7 One more cavity to be controlled

8. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Fluctuation-dissipation theorem: Thermal noise: mirrors, wires, pendulum Possible cures: reduce dissipation or cool the mirrors Thermal Noise by D.Crooks

9. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Detector scheme Laser 20 W Output Mode Cleaner 3 km long Fabry-Perot cavities: to lengthen the optical path to 100 km Input Mode Cleaner Power recycling mirror: to increase the light power to 1 kW

10. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Interferometers network TAMA 600 m 300 m 4 & 2 km 4 km AIGO 3 km False alarm rejection will require coincidences ITFs have little directionality: at least 3 detectors are necessary to reconstruct the source direction

11. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino FRANCE - CNRS ESPCI – Paris IPN – Lyon LAL – Orsay LAPP – Annecy OCA - Nice ITALY - INFN Firenze-Urbino Frascati Napoli Perugia Pisa Roma Inaugurated July 2003

12. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Sensitivity Goal seismic thermal shot Wideband detector! LIGO First attempt to extend the detection band down to a few Hz!

13. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino HIGH SENSITIVITY REQUIRES SMART TECHNOLOGY

14. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Vacuum Requirements: –10 -9 mbar for H 2 –10 -14 mbar for hydrocarbons Vacuum pipe: –1.2 m diameter –Baked at 150 °C for 1 week or more

15. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Laser 20 W, Nd:YVO 4 laser, two pumping diodes Injection locked to a 0.7 W Nd:YAG laser Required power stability:  P/P~10 -8 Hz -1/2 Required frequency stability: 10 -6 Hz 1/2 Laser cavity

16. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Input Mode Cleaner Mode cleaner cavity: filters laser noise, select TEM 00 mode Input mode-cleaner: dihedron Input mode-cleaner: curved mirror Input beam Transm. beamRefl. beam

17. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Mirrors High quality fused silica mirrors 35 cm diameter, 10 cm thickness, 21 kg mass Figures: –Substrate losses: 1 ppm –Coating losses: <5 ppm –Surface deformation: /100

18. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Output Optics Light filtering: output mode cleaner, 3.6 cm long monolithic cavity Light detection: InGaAs photodiodes, 3 mm diameter, 90% quantum efficiency Suppression of TEM 01 by a factor of 10 Length control via temperature (Peltier cell) Detection bench Output Mode-Cleaner

19. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Superattenuators Inverted pendulum pre-isolation stage Cantilever blades+magnetic antisprings for vertical isolation 3 actuation points for hierarchical control of the mirror: inverted pendulum, marionette, recoil mass First and only attempt to extend the sensitivity bandwidth down to a few Hz Blade springs Magnetic antisprings

20. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Passive Isolation performance Expected seismic displacement of the mirror (red curve) compared with natural seismic noise Thermal noise is dominant above 3 Hz Isolation sufficient also for “advanced” interferometers Active damping of the resonances at the top stage level Thermal noise

21. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino ITF Operation Conditions Keep the FP cavities in resonance –Maximize the phase response Keep the PR cavity in resonance –Minimize the shot noise Keep the output on the “dark fringe” –Reduce the dependence on power fluctuations Keep the armlength constant within 10 -12 m !

22. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Interferometer control Photodiodes Bx provide the error signals to control the 4 independent length of the interferometer Quadrant photodiodes provide the error signals to control the angular positions of the mirrors

23. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Limited dynamic range requires to split forces over more control stages Hierarchical Control DC-0.01 Hz 0.01-8 Hz 8-50 Hz 10 mN Force applied to the mirror (a.u.) without hierarchical control Force applied to the mirror with hierarchical control (same a.u.) with tidal control & re-allocation to the marionette 1 mN

24. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Towards the Target sensitivity Start of full VIRGO commissioning: July 2003 One cavity locked: autumn 2003 Recombined ITF locked: Feb 2004 Power recycling locked: Oct 2004 >10 4 1 year Extragalactic sensitivity to NS/NS coalescences 55 kpc

25. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Understanding the detector Measure the sensitivity  identify the noise sources  try to reduce the noise

26. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Inaugurated at the end of 1999 Path to target sensitivity: more than 3 years LIGO commissioning path May 01 Aug 04 More than 3 years…

27. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino GW ASTRONOMY ??

28. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino How Many Events? COALESCING COMPACT BINARIES Expected rate of coalescences: 3/yr out of 40  200 Mpc [Grishchuk et al., astro-ph/0008481] Waveform accurately predicted: VIRGO/LIGO can detect a NS/NS event at ~ 20 Mpc Detection rate (best estimates): a few/yr [Burgay et al., Nature, 2003]

29. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Expanding the Accessible Universe Where and how can we reduce the detector noise? Seismic Thermal Shot – High power laser – Better optics – QND techniques – New materials – Cryogenic interferometers No further suppression

30. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Advanced LIGO (2009+) Higher power laser (10 W  180 W) New seismic isolation system (active) Fused silica suspension wires 40 kg sapphire mirrors Signal recycling Initial LIGO Advanced Interferometers Open up wider band ~ 15 in h ~3000 in rate NS/NS detectable @300 Mpc by R.Powell from LIGO Virgo/LIGO range Adv. LIGO range LIGO figures

31. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Advanced Virgo Virgo already has “advanced” vibration isolator: feasible with minor changes to the current detector New low dissipation suspension fibers and mirrors to reduce thermal noise New laser and optics to reduce shot noise Possible use of a new optical configuration (signal recycling) Also GEO600 and TAMA are thinking about 2nd generation detector

32. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino Towards a worldwide network The trans-Atlantic side: GEO is part of LIGO Science Community, full agreement for data exchange LIGO-Virgo MOU to be signed soon –Topic driven collaboration, initially focused on two defined subjects (inspirals and bursts) –Real joint analysis will start when comparable sensitivity will be reached The European side: A collaborative effort is starting in Europe (Virgo-GEO) Common working group have been set up in the ILIAS-GWA framework

33. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino GW-WWW 3 km TAMA

34. Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino