Interferometric detector for GW: status and perspectives Giovanni Losurdo INFN Firenze-Urbino...
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Transcript of Interferometric detector for GW: status and perspectives Giovanni Losurdo INFN Firenze-Urbino...
interferometric detector for GW:status and perspectives
Giovanni LosurdoINFN Firenze-Urbino
e-mail: [email protected]
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
The ultimate goal
GW astronomy: a new window on the universe
GW ??
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
1
2L hL
Need to measure: L ~ 10-18 m
Target h ~ 10-21
(NS/NS @Virgo Cluster)
Big challenge for experimentalists!
Interference fringes
Feasible L ~ 103 m
LIGO figures
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
Pout depends also on Pin , L.
ITF sensitive to power and frequency fluctuations, displacement noises, …
A simple detector
4gw L h
20cos ( )out in gwP P
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
2 1 shot shot
ch
P L P
23
21
3 10 / Hz
10
shot
shot
h
h
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 ddL• Drawback: works only at
resonance
2'
FL L
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
1 kW Power?
Interferometer Ecology: recycle the wasted light!
• Peff= Recycling factor ·Pin 20 W 1 Kwatt
• Shot noise reduced by a factor 7• One more cavity to be controlled
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
)(4)(~2 fTkfF B
by D.Crooks
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
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
Interferometers network
TAMA600 m
300 m4 & 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
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
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!
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
HIGH SENSITIVITY
REQUIRES
SMART TECHNOLOGY
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
Vacuum• Requirements:
– 10-9 mbar for H2
– 10-14 mbar for hydrocarbons• Vacuum pipe:
– 1.2 m diameter– Baked at 150 °C for 1 week or more
1.00E-14
1.00E-13
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
0 10 20 30 40 50 60 70 80 90 100
mass/charge
pa
rtia
l pre
ssu
re,
mb
ar
After bake
before bake
Residual Gases in tube900m - 1500m N
October 2001 Ptot=3E-8 mbar
Ptot=2E-10 mbar
2: hydrogen18: water12,28: carbon monoxide44: carbon dioxide55, 57: hydrocarbon contamination
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
Laser• 20 W, Nd:YVO4 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 Hz1/2
Lasercavity
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
Input Mode Cleaner• Mode cleaner cavity: filters laser
noise, select TEM00 mode
Input mode-cleaner: dihedron
Input mode-cleaner: curved mirror
refbeaminbeam outbeam
Input beam Transm. beam Refl. beam
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
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 TEM01 by a factor of 10
• Length control via temperature (Peltier cell)
Detection bench
Output Mode-Cleaner
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
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
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 !
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
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 with tidal control & re-allocation to
the marionette
1 mN
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
>104
1 yearExtragalactic sensitivity to NS/NS coalescences
55 kpc
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
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 04More than 3 years…
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
GW ASTRONOMY ??
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]
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
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
Advanced LIGO (2009+)• Higher power laser (10 W180 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 M
pc
by R.Powell
from LIGO
Virgo/LIGO range
Adv. LIGO rangeLIGO figures
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
1 10 100 1000 1000010-24
10-23
10-22
10-21
10-20
10-19
10-18
10-17
h(f)
[1/s
qrt(H
z)]
Frequency [Hz]
Virgo Adv Virgo
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
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino
GW-WWW
3 km
TAMA
Physics 2005 – Warwick, Apr. 13, 2005 G.Losurdo – INFN Firenze-Urbino