Gravitational Wave Detectors

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Gravitational Wave Detectors

• Course in Inflation, Structure formation and CMB
• 7 November 2002
• Silvio Orsi

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GW My presentation

• GW production
• Upper bounds on GW background
• Frequency range
• Detectors for GW
• Under construction future detectors
• Frequency range sensitivity
• Noise
• Examples

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GW Production

• GW background from amplification of vacuum
  fluctuations
• Standard inflation
• Pre-Big Bang cosmology
• Other models
• Known astrophysical sources
• Noise (unresolved astrophysical sources)
• On Earth Seismic noise

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GW Background

• Origin
• Characteristics isotropic, stationary,
  unpolarized
• Main property frequency spectrum
• 3 useful characterizations
• Energy density
• Spectral density
• Characteristic amplitude

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GW Background (ex.)
http//www.ba.infn.it/gasperin/
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Upper bounds on Energy Density
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Frequency range

• From theories
• Measurable

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GW spectrum
http//www.its.caltech.edu/esp/lisa/gwspectrum.gi
f
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GW Detectors

• Existing detectors give upper bounds
• Resonant mass experiments EXPLORER (CERN),
  NAUTILUS (I), AURIGA (I), ALLEGRO (Louisiana),
  NIOBE (Aus)
• Interferometers
• Large-scale (under construction) LIGO, VIRGO
  (I,F), GEO600 (D), TAMA300 (Jap), AIGO (Aus)
• Second generation (planned) LISA (space
  interf.), Advanced LIGO
• Two-interferometer correlation
• (Pulsars)

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Binary Pulsar (GW discovery)
Pulsars are very good detectors for GW for their
stability
http//zebu.uoregon.edu/imamura/talks/gravity_wav
es/psr1913.html
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Resonant mass experiments

• Bars are narrow-band detectors and work at two
  resonances
• f 1kHz
• Half-heigth bandwiths 1Hz
• Strain sensitivity 5x interferometers
• Optimization (Quality factor x Mass) /
  Temperature
• AURIGA

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AURIGA

• Ultracryogenic Resonant Antenna for the
  Gravitational Astronomical Investigation
• Resonant acoustic detector
• Resonator Aluminium bar (length3m,
  diameter60cm, mass2.3t, T100mK, TeffmK,
  quality factor Q106)
• Signals _at_ 1kHz

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AURIGA
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AURIGA
NEW!

• Sensitivity Improvement
• with Optical
• Read-out

OLD
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Other Resonance-Projects

• Projects at a preliminary stage
• TIGA (Truncated Icosahedral Gravitational Wave
  Antenna), Louisiana first resonant mode 3.2kHz
• SFERA (Rome) large spherical detector (40-100t)
  competing with interferometers (h10-24 !)

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Interferometer principles

• Wide-band detectors (few Hz ? kHz)
• Description (see fig.)
• Sensitivity
• Noise (seismic, resonances, laser shot)

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Typical sensitivity curve
RESONANCE REGION
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Interferometer Location on Earth
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Two-interferometer correlation

• Dramatic increase in sensitivity
• Interf-interf
• Interf-res. mass
• Not applicable to LISA

5x10-11
Advanced LIGO
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VIRGO

• Pisa (Italy)
• Arm length 3km
• Large collaboration 11 laboratories (I,F) 200
  people
• Sensitivity

http//www.virgo.infn.it
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VIRGO
http//wwwlapp.in2p3.fr/virgo/gwf.html
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VIRGO Sensitivity
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First VIRGO engineering run (2001)
Michelson-interferometer configuration
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LIGO
Laser Interferometer Gravitational Wave
Observatory

• Will evolve into LIGOIII with a sensibility 10x
  better than LIGOI

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Smaller interferometers

• GEO600 (Hannover) L600m, smaller than VIRGO,
  LIGO new techniques (signal recycling mirror)
  are used for 2nd generation interf.
• TAMA300 (Japan), L300m evolution into LGRT
  (Laser Gravitational Radiation Telescope) near
  SuperKamiokande detector (?)
• AIGO (Aus) southern emisphere (!)

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LISA
Laser Interferometer Space Antenna

• Proposed by ESA (1993)
• NASA/ESA collaboration
• Launch estimated 2010-2020
• Mission 2yrs (up to 10)
• 3 arms (redundancy)
• Common noise (3 non-indep. interf.)
• NSR (noise to signal ratio) negligible
• Info on GW polarization direction

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LISA (2)
Laser Interferometer Space Antenna

• Better discrimination of GW stochastic bg,
  binaries, cosmological effects instrumental
  noise
• No seismic gravity-gradient noise
• Frequency range 10-4 Hz ? 1 Hz
• Very long length (L5x106 km)
• Strain sensitivity_at_1mHz 4x10-21 Hz 1/2

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LISA (3)
Laser Interferometer Space Antenna

• Frequency range 10-4 Hz ? 1 Hz
• Best sensitivity 3?30 mHz
• fgt30mHz ?GWlt2L
• flt3mHz spurious forces on test masses
• Low f expected bg from white-dwarfs binaries

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LISA (sensitivity)
Laser Interferometer Space Antenna