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 ??


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


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


• 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


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


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


• 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


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


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


FRANCE - CNRS

• ESPCI – Paris

• IPN – Lyon

• LAL – Orsay

• LAPP – Annecy

• OCA - Nice

ITALY - INFN

• Firenze-Urbino

• Frascati

• Napoli

• Perugia

• Pisa

• Roma

Inaugurated July 2003


Sensitivity Goal

seismic

thermal

shot

Wideband detector!

LIGO

First attempt to extend the detection band down to a few Hz!


HIGH SENSITIVITY

REQUIRES

SMART TECHNOLOGY


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


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


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


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


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


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


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


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 !


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


• 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


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


Understanding the detector• Measure the sensitivity identify the noise sources try to reduce the

noise


• Inaugurated at the end of 1999• Path to target sensitivity: more than 3 years

LIGO commissioning path

May 01

Aug 04More than 3 years…


GW ASTRONOMY ??


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]


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


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


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


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


GW-WWW

3 km

TAMA

interferometric detector for gw: status and perspectives giovanni losurdo infn firenze-urbino...

Documents

light power

output mode cleaner

ultimate power fluctuations

kwattshot noise

dihedroninput modecleaner

filters laser noise

tem00 modeinput modecleaner

length control