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Absolute displacement calibration in LIGO

Absolute displacement calibration in LIGO. Rick Savage LIGO Hanford Observatory Discussion with UTB Students March 7, 2012. Laser Interferometer Gravitational-wave Observatory. What ? A new kind of astronomical observatory – sensing gravitational waves Why ?

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Absolute displacement calibration in LIGO

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  1. Absolute displacement calibration in LIGO Rick Savage LIGO Hanford Observatory Discussion with UTB Students March 7, 2012

  2. R. Savage UTB Students March 7, 2012 Laser InterferometerGravitational-wave Observatory • What ? • A new kind of astronomical observatory – sensing gravitational waves • Why ? • To observe the Universe through a new window – with a new sense. Like hearing in addition to seeing. • How ? • A network of ultra-sensitive, kilometer-scale laser interferometers measuring minute variations in photon propagation times. • When ? • Initial phase of LIGO completed on Oct. 20, 2010 • Advanced LIGO detectors currently under construction – plan to be operating by 2014. • Expect detections at least once per month – otherwise something fundamentally wrong with our understanding of physics/astrophysics

  3. R. Savage UTB Students March 7, 2012 Potential sources • Coalescing Binary Systems • neutron stars • low mass black holes • NS/BS systems • Burst Sources • galactic asymmetric core collapse supernovae • cosmic strings • ??? • Continuous Sources • spinning neutron stars • probe crustal deformations • Cosmic GW background • stochastic incoherent background Credit: AEI, CCT, LSU Credit: Chandra X-ray Observatory Casey Reed, Penn State NASA/WMAP Science Team

  4. R. Savage UTB Students March 7, 2012 LIGO detectors Power recycled Michelson interferometer with Fabry-Perot arm cavities 4 km-long Fabry-Perotarm cavity test masses recycling mirror Laser beam splitter signal

  5. R. Savage UTB Students March 7, 2012 H1 detector sensitivity – July 10, 2010 10-19 meters S6 science run – July 2009 to October 2010

  6. R. Savage UTB Students March 7, 2012 Capturing the waveform • Source localization and waveform reconstruction require absolute displacement calibration with accuracy at the level of 5% and eventually even 1% Sketch: Kip Thorne

  7. R. Savage UTB Students March 7, 2012 LIGO displacement calibration - comparison of three methods • Free-swinging Michelson • Photon calibrator • Laser frequency modulation +,- 5%

  8. R. Savage UTB Students March 7, 2012 Photon Calibrator method Use a power-modulated auxiliary laser to displace the mass via the recoil of the photons (in “Science mode” configuration). Conceptually simple, single-step, on-line method

  9. R. Savage UTB Students March 7, 2012 Absolute laser power calibration –traceable to NIST

  10. R. Savage UTB Students March 7, 2012 eLIGO Pcal Upgrade

  11. R. Savage UTB Students March 7, 2012 eLIGO Implementation

  12. R. Savage UTB Students March 7, 2012 Swept-sine Analysis Accomplishments:Actuator Stability, Swept-Sines • Stability of Actuation ±1%

  13. R. Savage UTB Students March 7, 2012 But …..Pcal forces deform the test mass Local elastic deformation P. Daveloza, N. Konverski, et al. UTB

  14. R. Savage UTB Students March 7, 2012 And excite bulk deformations Drumhead mode Butterfly mode Pablo Daveloza UTB

  15. R. Savage UTB Students March 7, 2012 Mitigation…..Precise location of Pcal forces Comsol finite element modeling(P. Daveloza) Locate two beams at radial positions that minimize excitation of the drumhead mode

  16. R. Savage UTB Students March 7, 2012 H1, H2 Optical Layouts

  17. R. Savage UTB Students March 7, 2012 H1, L1 Hardware Locations

  18. R. Savage UTB Students March 7, 2012 MechanicalIn-vacuum Hardware Transmit periscopes Receive periscopes ETM Camera periscopes

  19. R. Savage UTB Students March 7, 2012 “The devil is in the details …..”

  20. R. Savage UTB Students March 7, 2012 Pcal work here at UTB…..ask Pablo

  21. R. Savage UTB Students March 7, 2012 Free-swinging Michelson method Use laser wavelength (1064 nm) as a length reference and bootstrap ETM calibration via a series of measurements Record free-swinging (short) Michelson signal at AS port. Lock short Michelson config. and measure OLTF Measure ITM to AS signal TF Lock single arm and measure ETM/ITM TF ITM AS Now using asymmetric Michelson technique to simplify this method ITM ETM AS

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