1 / 45

Stefan Ballmer Fermilab May 14, 2013

Experimental Challenges in Gravitational-Wave Astronomy. Stefan Ballmer Fermilab May 14, 2013. Outline. Introduction: The sensitivity of Advanced LIGO What can we achieve in the next 2 decades? Science case: GW astrophysics Technological challenges & required R&D. Gravitational Waves.

gautam
Download Presentation

Stefan Ballmer Fermilab May 14, 2013

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Experimental Challenges in Gravitational-Wave Astronomy Stefan Ballmer Fermilab May 14, 2013

  2. Outline • Introduction: The sensitivity of Advanced LIGO • What can we achieve in the next 2 decades? • Science case: GW astrophysics • Technological challenges & required R&D

  3. Gravitational Waves “Curvature ofSpace-Time” “Matter” NASA/Dana Berry, Sky Works Digital

  4. The wave’s field “Ripples in Space-Time” Measureable effect: Stretches/contracts distance between test masses perpendicular to propagation Amplitude: dL/L = h Image credit: Google + polarization x polarization 4

  5. The weakness of Gravity Gravitational waves produced by orbiting masses: For 2 1.4MSun Neutron stars, at 1 Mpc (3 million light years): NASA/Dana Berry, Sky Works Digital

  6. The beginning of LIGO • Electromagnetically coupled broad-band gravitational wave antenna, R.Weiss, MIT RLE QPR 1972 • NSF funding andconstruction inthe 1990’s

  7. LIGO Livingston Observatory LIGO Hanford Observatory

  8. Currently installing Advanced LIGO…

  9. Michelson Interferometer + Fabry-Perot Arm Cavities + Power Recycling + Signal Recycling 1064 nm ~2x10-12Hz-1/2 200 4000 m Laser Interferometer Sensitivity:Quantum noise end test mass 4 km Fabry-Perot cavity recycling mirror input test mass 800kW 6kW 125 W 50/50 beam splitter GW signal (Numbers for aLIGO design)

  10. Advanced LIGONoise Budget

  11. NS-NS standard candle(sky-averaged distances) Initial LIGO:20 Mpc Advanced LIGO: 200Mpc Expect ~40 / year From population synthesis (Class.Quant.Grav.27:173001,2010 ) Or from SHGRB rate, taking into account beaming TypicalShort-HardGRBs

  12. Outline Introduction: The sensitivity of Advanced LIGO What can we achieve in the next 2 decades? Science case: GW astrophysics Technological challenges & required R&D

  13. GW Astronomy Science Goals • Fundamental Physics • Is GR the correct theory of gravity? • Do black holes really have “no hair” ? • What is the neutron star equation of state? • Astrophysics • What is the black hole mass distribution? • How did supermassive BHs grow? • What are the progenitors of GRBs? • Cosmology • Can we directly see past the CMB?

  14. What is needed to achieve this? • Advanced LIGO will observe NS/NS mergers, but it is a detection machine • SNR = 10  signal fidelity ~10% • Many interesting science goals out of reach • We want to see NS/NS mergers to cosmological distances • …that is where we observe GRB’s… • We need better sensitivity… • …probably in 2 stages… G. Galilei

  15. NS-NS standard candle(sky-averaged distances) Initial LIGO:20 Mpc Advanced LIGO: 200Mpc Expect ~40 / year Future aLIGO upgrade Observe NS-NS mergers up toredshift ~0.2 Expect O(2)/week Multi-messenger observationson a regular basis TypicalShort-HardGRBs

  16. The science case for the next generation GW detector • aLIGO • Upgrade to aLIGO • Next generation • Observe NS-NS mergers larger than redshift 1 • Expect O(10)/day

  17. Expected noise in context Initial LIGO Advanced LIGO Facility upgrade Ultimate goal(new facility, Einstein class)

  18. What about IMBHs? Exploring the Early Relativistic Universe with Intermediate Mass Black Holes. The existence of intermediate-mass black holes (IMBHs) is an open question in astrophysics. M

  19. Outline Introduction: The sensitivity of Advanced LIGO What can we achieve in the next 2 decades? Science case: GW astrophysics Technological challenges & required R&D

  20. Advanced LIGONoise Budget

  21. Key technological hurdles Quantum noise (radiation pressure/shot) Quantum mechanical measurement limitations Thermal noise (coating) Thermal motion of the mirror surface Newtonian (Gravity Gradient) noise Newtonian gravity short-circuits suspensions(not this talk)

  22. Quantum Noise Go heavy… Squeezing External squeezed light injection Filter cavities

  23. Squeezed light source • Quantum trade-off between phase and amplitude noise • Strain sensing is only sensitive to one of them Ep-quadrature Schematic representationof Electric field, various states Ex-quadrature

  24. Why does squeezing work? Laser Readout quadrature

  25. Filter cavities Concept: A cavity operatedin reflection: frequency dependent phase shift No delay above cavity pole Used on squeezed light: frequency dependent rotation on squeezing ellipse Keep squeezing ellipse in correct orientation Draw-back: very sensitive to optical losses Φ(f)

  26. Thermal Noise - basics Fluctuation-dissipation theorem: It’s the loss! Equipartition theorem.: Fluctuation-dissipation theorem The energy loss per cycle (normalized by the driving force squared) is proportional to the velocity power spectrum vs.

  27. Types of Thermal Noise 2 types of losses: Mechanical loss  Brownian noise direct coupling to elastic strain Thermal loss  Thermo-optic noise thermo-elastic (coupling through thermal expansion) thermo-refractive (coupling through dn/dT) ...are coherent

  28. Thermal Noise - basics Two main sources: Suspension Thermal Noise Due to mechanical losses in suspension wires Use long monolithic suspensions Coating thermal noise Due to mechanical loss in optical coating Hard to fix…

  29. Mitigating Thermal Noise… Arm length ( pricy ) Beam size ( instability ) Increase sampled mirror area: Laguerre-Gaussian modes Effective beam area larger (Noise averages) But mode degenerate Or…

  30. Realizing multiple spots • Use multiple spots… • Coating thermal noise becomes (mostly) uncorrelated (Nakagawa et. al. PRD, vol 65, 082002) • An idea with a twist: • … closed as FB cavity after N-bounces (N<10) (APPLIED OPTICS, Vol. 4, No. 8 (1965) ) Example: 4.5-spot standing-wave cavity

  31. Cryogenic operation • Thermal Noise? Cool! • Young’s modulus, mech. loss, thermalconductivity and capacity need to bewell-behaved at low T. • New substrate materiale.g. crystalline Si (aLIGO uses SiO2) • Implications: • Need to change laser wavelength to 1.6u (band edge) • Affects coating choice • Technical integration challenge • Vibrations, cooling beam pipes, etc.

  32. Crystal coatings Switch from amorphous to crystalline coating Lower mechanical loss ~10-5 lower Brownian noise(aLIGO: Ta2O5 has loss angle ~2.3e-4) Options: AlGaAs: grows on GaAs Requires lift-off & bonding AlGaP: Lattice-matched Grows on Si

  33. Crystal coatings - AlGaAs Recent result: Tenfold reduction of Brownian noise in optical interferometry (G. Cole et. al.,arXiv:1302.6489) Loss angle < 4e-5 G.Cole, W. Zhang, M. Martin, J. Ye,M. Aspelmeyer

  34. Crystal coatings:Remaining Issues Dominated by thermo-optic noise in LIGO band Cancellation mechanisms betweenthermo-elastic and thermo-refractivecan be exploited Lift-off and bonding forLIGO-size optics non-trivial Phys.Rev.D78:102003,2008Evans, Ballmer, Fejer, Fritschel, Harry, Ogin G.Cole, VCQ,M.Martin, C. Benko, J. Ye JILA G.Cole, W. Zhang, M. Martin, J. Ye,M. Aspelmeyer

  35. So what can we expect? Where can we get to with these ideas?

  36. ‘’RGB’’ design study Simple design studiesfor aLIGO upgrades. 3 teams formed: Blue (headed by R.Adhikari) Red (headed by S.Hild) Green (headed by myself) Constraints: Use existing LIGO vacuum systems Keep as many existing aLIGO systems as possible LIGO Hanford Observatory

  37. ‘’RGB’’ design study Questions: How much improvement over aLIGO is possible? What is the budget? What are the trade-offs? Can the upgrade happen incrementally? When do we need to be ready? What R&D needs to be carried out?

  38. An upgrade for Advanced LIGO

  39. The answer is 42…

  40. Mirror Thermal Noise

  41. Parameters aLIGO coatings! 4-spot standing wave resonant delay line 1.5x spot radius increase Mass: 160kg Suspension and Newtonian noise: Copy RB Laser input: 125Watt (arm power lower…) 10dB frequency dependent squeezing

  42. RGB comparison

  43. Conclusion • Advanced LIGO will observe NS/NS mergers, and whet our appetite for more • A factor of 10x of sensitivity improvement (z=1 for NS/NS) seems possible, but requires research • A factor of 3x is possible at existing sites • The scientific pay-off would be enormous

  44. Thank you!

More Related