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Physics of LIGO Lecture 4

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Physics of LIGO Lecture 4 Physics of LIGO Lecture 4 40KG § Advanced LIGO SAPPHIRE, 31.4CMf SILICA, HERAEUS SV 35CMf INPUT MODE SILICA, LIGO I GRADE § LIGO Data analysis CLEANER ~26CMf ACTIVE THERMAL CORRECTION T=0.5% 125W 830KW LASER MOD. BS PRM ITM ETM time T~6% SRM T=7% OUTPUT MODE CLEANER PD Ringdowns GW READOUT Broadband Background Bursts frequency CW (quasi-periodic) Chirps LIGO-G000165-00-R AJW, Caltech, LIGO Project 1 Initial LIGO Þ Advanced LIGO schedule 1995 NSF Funding secured ($360M) 1996 Construction Underway (mostly civil) 1997 Facility Construction (vacuum system) 1998 Interferometer Construction (complete facilities) 1999 Construction Complete (interferometers in vacuum) 2000 Detector Installation (commissioning subsystems) 2001 Commission Interferometers (first coincidences) 2002 Sensitivity studies (initiate LIGO I Science Run) 2003+ Initial LIGO data run (one year integrated data at h ~ 10-21) 2007 Begin Advanced LIGO installation 2008 Advanced LIGO science run (2.5 hours ~ 1 year of Initial LIGO) LIGO-G000165-00-R AJW, Caltech, LIGO Project 2 Advanced LIGO incremental improvements § Reduce shot noise: higher power CW-laser: 12 watts Þ120 watts § Reduce shot noise: Advanced optical configuration: signal recycling mirror (7th suspended optic) to tune shot-noise response in frequency § Reduce seismic noise: Advanced (active) seismic isolation. Seismic wall moved from 40 Hz Þ ~ 12 Hz. § Reduce seismic and suspension noise: Quadrupal pendulum suspensions to filter environmental noise in stages. § Reduce suspension noise: Fused silica fibers, silica welds. § Reduce test mass thermal noise: Last pendulum stage (test mass) is controlled via electrostatic or photonic forces (no magnets). § Reduce test mass thermal noise: High-Q material (40 kg sapphire). § To handle thermal distortions due to beam heating: advanced mirror materials, coatings, thermal de-lensing compensation (heating mirror at edges) LIGO-G000165-00-R AJW, Caltech, LIGO Project 3 LIGO II predicted noise curves LIGO-G000165-00-R AJW, Caltech, LIGO Project 4 AdvLIGO configuration 40KG SAPPHIRE, 31.4CMf SILICA, HERAEUS SV 35CMf INPUT MODE SILICA, LIGO I GRADE CLEANER ~26CMf ACTIVE THERMAL CORRECTION T=0.5% 125W 830KW LASER MOD. BS PRM ITM ETM T~6% SRM T=7% OUTPUT MODE CLEANER PD GW READOUT LIGO-G000165-00-R AJW, Caltech, LIGO Project 5 Arm cavity parameters and LIGO sensitivity As rITM is increased, Garm is increased, fpol-arm fpol-arm is decreased. hdc ~ 1/ GarmPlaser Given other noise sources (seismic, thermal), choose rITM to optimize Sensitivity to binary inspirals LIGO-G000165-00-R AJW, Caltech, LIGO Project 6 Signal recycling, RSE § Problem: the transmissivity of the ITM (TITM) governs both the arm cavity gain (power available for sensing DL at f=0) and the light storage time / cavity pole farm § Need the ability to optimize these independently § The shot noise frequency dependence can be optimized (for fixed laser power) by adding one (or more) suspended optics at the dark port (signal recycling or RSE) § This permits independent control of cavity gain for the carrier and for the signal sidebands (audio frequencies of GW signal) § Make the arms high finesse to store lots of carrier light (allowing one to reduce gain in PRC), but low finesse for the GW signal sidebands to increase bandwidth: RSE § Combine power recycling (PR) and signal recycling (SR): Dual recycling (DR) LIGO-G000165-00-R AJW, Caltech, LIGO Project 7 Coupled cavity response Simplified analysis: • fold beam splitter + arms together • model as a single FP cavity • adding SM produces a coupled cavity • ITM+SM forms a compound mirror, with reflectivity 2 -if tITM rSM e rcm = rITM - -if With f = 2kls = 4pls(fcarr+fsig)/c 1- rITM rSM e LIGO-G000165-00-R AJW, Caltech, LIGO Project 8 Tuning the signal response By choosing the phase advance of the signal (fcarr+fsig) in the signal recycling cavity, can get longer (SR) or shorter (RSE) storage of the signal in the arms: f = 2kls = 4pls(fcarr+fsig)/c rCC rITM RSE tuned RSE SR (narrow band) SR The red curve corresponds to r = rITM, ie, no SR mirror LIGO-G000165-00-R AJW, Caltech, LIGO Project 9 Using DR to optimize sensitivity Now we can independently tune hDC and fpolarm to optimize sensitivity (eg, hug the thermal noise curve) LIGO-G000165-00-R AJW, Caltech, LIGO Project 10 Controlling the signal mirror § The other 6 mirrors (LIGO-I configuration) are controlled by reflection-locking: beat carrier (resonant in all cavities) off of RF sidebands § Here, with no GW, there is no carrier in signal cavity! § One solution: add another RF sideband; make one RF sideband resonant in signal cavity, the other isn’t; then, reflection locking will work. § Both RF sidebands must be resonant in PRC; and both must pass through the MC § Want to change the tune f = 2kls at will § This is a difficult, constrained problem. One reasonable solution will be prototyped at Glasgow and at the 40m. LIGO-G000165-00-R AJW, Caltech, LIGO Project 11 Control topology for Advanced LIGO ETMperp Carrier RF Sidebands f1 RF Sidebands f2 ITMperp Input Symm Port PRM ITMinline ETMinline Pickoff SRM Asym Port LIGO-G000165-00-R AJW, Caltech, LIGO Project 12 AdvLIGO controls LIGO-G000165-00-R AJW, Caltech, LIGO Project 13 LIGO II Active seismic isolation and multiple pendulum suspension • Must support LIGO test mass optic at the beamline. • Must fit inside existing vacuum chambers, and be fully vacuum compatible. • Must provide full control system. • Must satisfy specs: LIGO-G000165-00-R AJW, Caltech, LIGO Project 14 Active control of SEI system Coarse hydraulic actuators in air Optical table Sensors: seismometers, relative-position sensors Actuators: EM non-contacting forcers Two active stages: cages, masses, springs, S/A pairs. All DOF under active control. LIGO-G000165-00-R AJW, Caltech, LIGO Project 15 GEO multiple pendulum design • 3 or 4 pendulum stages; each 2 provides 1 / f filtering for f > f0 • Top stage has 6 OSEMs for 6-dof control (“marionetta”), relative to support cage. • Normal modes of the multiple pendulum (~24) must not have nodes at the top, so they can be controlled from the top. • Blade springs at the very top provide tuned vertical isolation. • Lower stages must control w.r.t. stage above it; so the actuators must push against a “reaction mass” which is as quiet as the stage above it • lowest stage (test mass optic) is attached to stage above it with fused silica fibers. Fused silica fibers LIGO-G000165-00-R AJW, Caltech, LIGO Project 16 COC, SEI, SUS R&D LIGO-G000165-00-R AJW, Caltech, LIGO Project 17 SEI + SUS Put them together; Test in LASTI LIGO-G000165-00-R AJW, Caltech, LIGO Project 18 Thermal compensation (de-lensing) methods • Beam heating at center of optic distorts the optic due to thermal expansion, changing ROC, index of refraction, etc. • Compensate by heating the optic from the circumference in, to give uniform and constant-in- time thermal loading as the IFO is operated. LIGO-G000165-00-R AJW, Caltech, LIGO Project 19 LIGO III… § More advanced optical design (Sagnac?) § non-transmissive optics (Sagnac)? § Cryogenically-cooled mirrors? § Different IFOs optimized for different frequency bands? § Beating the standard quantum limit: squeezed light; speed meter; frequency-dependent demodulation phase § Photon drive mirror actuation? LIGO-G000165-00-R AJW, Caltech, LIGO Project 20 The polarization Sagnac IFO § All reflective optics to minimize thermal distortions § Common path for interfering beams § Grating beam splitter (double- pass, to null dispersion) § Delay line arms § Heroic efforts to minimize noise due to scattered light § Polarization allows the light to exit the IFO at the symmetric port of the beam splitter § Many clever tricks to ensure robust control, low noise LIGO-G000165-00-R AJW, Caltech, LIGO Project 21 Prototype IFOs § Several table-top (non-suspended) IFOs for development of RSE/DR – Caltech (Jim Mason), UFla, ANU, TAMA 3 § 40 meter (Caltech) : full engineering prototype for optical and control plant for AdvLIGO § Thermal Noise Interferometer (TNI, Caltech) : measure thermal noise in AdvLIGO test masses (sapphire) § LIGO Advanced Systems Testbed IFO (LASTI, MIT) : full-scale prototyping of AdvLIGO seismic isolation & suspensions § Engineering Test Facility (ETF, Stanford) : Initial seismic isolation prototype; advanced IFO configs (Sagnac) § 10 meter IFO at Glasgow : prototype optics and control of RSE § TAMA 30 meter (Tokyo) : Advanced technologies (SAS, RSE, control schemes, sapphire, cryogenic mirrors) § AIGO 80m IFO at Gingin : high powered laser, thermal effects, control stability LIGO-G000165-00-R AJW, Caltech, LIGO Project 22 LIGO Data analysis § LIGO is a broad-band amplitude detector, measures waveforms. § The experimentalist thinks not in terms of astrophysical sources, but in terms of waveform morphologies. § Specific astrophysical sources suggest specific waveforms, but we don’t want to miss the unexpected! § Waveform morphologies being considered: » Bursts (of limited duration), for which we have models (chirps, ringdowns) » Bursts, for which we have no reliable models (supernovas, …) » Continuous waves, narrow bandwidth - periodic (pulsars) » Continuous waves, broad bandwidth - stochastic (BB background) § Each requires radically different data analysis techniques. § Algorithms, implementation development is in its infancy. LIGO-G000165-00-R AJW, Caltech, LIGO Project 23 Waveforms of Gravitational Waves § “Chirps” (reasonably known waveforms) » Neutron star (NS/NS) binary pairs » Black hole (BH/BH) binaries; NS/BH binaries § Periodic
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