Advanced LIGO David Shoemaker Aspen at Elba 23 May 2002 Advanced LIGO G020243-00-D 1 Core notions for the LIGO Lab future Evolution intrinsic to LIGO mission: to enable the development of gravitational wave astronomy Next step in detector design: Should be of astrophysical significance if it observes GW signals or if it does not Should be at the limits of reasonable extrapolations of detector physics and technologies Should lead to a realizable, practical instrument Much effort is inextricably entwined with LSC research LIGO Lab and other LSC members in close-knit teams R&D and designs discussed here are from the Community including the Lab Advanced LIGO G020243-00-D 2 Choosing an upgrade path
Wish to maximize astrophysics to be gained in the coming decade Must fully exploit initial LIGO Any change in instrument leads to lost observing time at an Observatory Studies based on LIGO I installation and commissioning indicate 11.5 years between decommissioning one instrument and starting observation with the next Want to make one significant change, not many small changes Technical opportunities and challenges Can profit from evolution of detector technologies since the freezing of the initial LIGO design Fundamental limits: quantum noise, thermal noise, Newtonian background provide point of diminishing returns (for now!) Advanced LIGO G020243-00-D 3 Present, Advanced, Future limits to sensitivity Advanced LIGO Seismic noise 4010 Hz Thermal noise 1/15 Shot noise 1/10, tunable Initial Advanced: factor <1000 in rate
Facility limits Gravity gradients Residual gas (scattered light) Beyond Adv LIGO Seismic noise: Newtonian background suppression Thermal noise: cooling of test masses Quantum noise: quantum non-demolition Advanced LIGO G020243-00-D 4 Top level performance & parameters Parameter LIGO I LIGO II Equivalent strain noise, minimum 3x10-23/rtHz 2x10-24/rtHz Neutron star binary inspiral range 19 Mpc 300 Mpc
Stochastic background sensitivity 3x10-6 1.5-5x10-9 Interferometer configuration Power-recycled MI w/ FP arm cavities LIGO I, plus signal recycling Laser power at interferometer input 6W 125 W Test masses Fused silica, 11 kg Sapphire, 40 kg Seismic wall frequency 40 Hz 10 Hz Beam size 3.6/4.4 cm 6.0 cm
Test mass Q Few million 200 million Suspension fiber Q Few thousand ~30 million Advanced LIGO G020243-00-D 5 Anatomy of the projected detector performance Seismic cutoff at 10 Hz Suspension thermal noise Internal thermal noise Unified quantum noise dominates at most frequencies technical noise (e.g., laser frequency) levels held, in general, well below these fundamental noises Optical noise Int. thermal
Advanced LIGO G020243-00-D 6 Design overview 40 KG SAPPHIRE TEST MASSES ACTIVE ISOLATION QUAD SILICA SUSPENSION 200 W LASER, MODULATION SYSTEM Advanced LIGO G020243-00-D 7 Advanced LIGO Development Team Group CIT MIT LLO LHO Seismic Suspension Isolation (SEI) (SUS) Core Optics Input Optics (COC) (IO)
Pre-Stab. Aux. Optics Ifo Sense & Laser (PSL) (AOS) Control (ISC) Systems Engineering requirements requirements; leads design; requirements; Fiber & bonding coordinates materials develop.; research; final design; TNI noise polishing; inhomogeneity requirements; intensity measure compensation; metrology stabilization feedback to PSL requirements; engin support & epics integration; performance requirements; photon eval. actuation; requirements; electronics; system identification; 40m experiment/controls testbed requirements; standards; extend E2E simulation; system trade studies; optical layout; FFT studies requirements; LASTI prototype testing requirements; measure coating effect on Q; LASTI prototype testing
requirements; integrated IO/PSL system test requirements; LASTI prototype requirements; active thermal & IO/PSL integrated sys test compensation requirements; system trade studies; bench top DC read-out exp.; PD testing; ISC design lead requirements; define noise budget, define shared signal port power allocation, etc. high power system testing injection-locked, stable/unstable resonator requirements engineering support Stanford/HP ACIGA Melody code welding; coating effect on mech Q; local control studies; triple performance in GEO-600; prelim design lead GEO/ Glasgow GEO/ Hannover
IAP PS Iowa LSU MSU Stanford 10m signal recycling exp.; lock acq. & sensing matrix guidance Rod pumped system; leads PSL system design in-situ figure metrology high power Faraday isolator development Bench code coating mech modeling MIMO control; SEI design lead transient (excess) noise measure; mode coupling study & diagnostics chem & flame polishing effect on Q; surface charge measure hydraulic pre-isolation; ETF controls welding, bonding & coating effect low absorption sapphire testbed on mech Q; bonding strength development MOPA system with LIGO 20W MO high mech Q, low absorption coatings direct loss measure; effect of
polishing, coating, bonding IO system design; high power component tests Advanced LIGO G020243-00-D back-illuminated InGaAs detectors trace element identification; absorption Southern U SMA/Lyon Syracuse UFL cavity test of active thermal compensation 8 Interferometer Sensing & Control Signal and power recycling Considering DC (fringe offset) readout GEO 10m proof of concept experiment: Preparation proceeding well Results for 40m Program in early 2003 (lock acquisition experience, sensing matrix selection, etc.) 40m Lab for Precision Controls Testing:
Infrastructure has been completed (i.e. PSL, vacuum controls & envelope, Data Acquisition system, etc.) Begun procurement of CDS and ISC equipment Working on the installation of the 12m input MC optics and suspensions, and suspension controllers by 3Q02 Advanced LIGO G020243-00-D 9 Seismic Isolation Choice of 10 Hz for seismic wall Allows Newtownian background to dominate Low Frequency regime may pursue suppression Achieved via high-gain servo techniques, passive multiple-pendulum isolation Isolation design has 3 stages: External pre-isolator: reduces RMS, 0.1 10 Hz Two in-vacuum 6 DOF stages, ~5 Hz natural resonant frequency, ~50 Hz unity gain Hierarchy of sensors (position, Streckeisen seismometers, L4-C geophones) Second-generation prototype in assembly and test at Stanford Advanced LIGO
G020243-00-D 10 Seismic Isolation: Pre-Isolator External pre-isolator development has been accelerated for possible deployment in initial LIGO to address excess noise at LLO Feedback and feed-forward to reduce RMS Hydraulic, electro-magnetic variants Prototype to be tested in LASTI mid-2002 BSC Initial LIGO passive SEI stack built in the LASTI BSC Plan to install pre-isolator at LLO 1Q/2003 HAM Advanced LIGO G020243-00-D 11 Suspensions Adaptation of GEO/Glasgow fused-silica suspension Quad to extend operation to ~10 Hz Suspension fibers in development Development of ribbons at Glasgow
Modeling of variable-diameter circular fibers at Caltech allows separate tailoring of bending stiffness (top and bottom) vs. stretch frequency Choosing vertical bounce frequency 12 Hz Can observe below (to Newtonian limit) Investigating 12 line removal techniques to observe to within a linewidth of bounce frequency Attachment of fibers to sapphire test masses Hydroxy-catalysis bonding of dissimilar materials Silica-sapphire tested, looks workable Advanced LIGO G020243-00-D 12 LASTI Laboratory LIGO-standard vacuum system, 16-m L Enables full-scale tests of Seismic Isolation and Test Mass Suspension Allows system testing, interfaces, installation practice. Characterization of non-stationary noise, thermal noise. Pre-stabilized laser in commissioning, 1m in-vacuum test cavity Pursuing wider-bandwidth fast loop configuration Will also be used for Adv LIGO intensity stabilization work
Pre-isolator work for initial LIGO has taken upper hand Initial LIGO isolation system installed Advanced LIGO seismic isolation to arrive in 2003, suspensions to follow Advanced LIGO G020243-00-D 13 Sapphire Core Optics Developing information for Sapphire/Fused silica choice Mechanical Q (Stanford, U. Glasgow) Q of 2 x 108 confirmed for a variety of sapphire substrate shapes Thermoelastic damping parameters Measured room temperature values of thermal expansion and conductivity by 2 or 3 (or four!) methods with agreement Optical Homogeneity (Caltech, CSIRO) New measurements along a crystal axis are getting close to acceptable for Adv LIGO (13 nm RMS over 80mm path) Some of this may be a surface effect, under investigation Advanced LIGO
G020243-00-D 14 Homogeneity measurements Measurement data: m-axis and a-axis Advanced LIGO G020243-00-D 15 Sapphire Core Optics Effort to reduce bulk absorption (Stanford, Southern University, CS, SIOM, Caltech) LIGO requirement is <10 ppm/cm Recent annealing efforts are encouraging Stanford is pursuing heat treatments with forming gas using cleaner alumina tube ovens; with this process they saw reductions from 45ppm/cm down to 20ppm/cm Higher temperature furnace commissioned at Stanford Demonstration of super polish of sapphire by CSIRO (150mm diameter, m-axis) Effectively met requirements Optical Homogeneity compensation
Ion beam etching, by CSIRO 10 nm deep, 10 mm dia, 90 sec Microroughness improved by process! Also pusuing pencil eraser approach with Goodrich, good results Advanced LIGO G020243-00-D 16 Coatings Mechanical losses of optical coatings leading to high thermal noise starting to understand where losses are SMA/Lyon (France) pursuing a series of research coating runs to understand mechanical loss multi-layer coating interfaces are not significant sources of loss most significant source of loss is probably within the Ta2O5 (high index) coating material; investigating alternative now investigating, with SMA/Lyon, the mechanical loss of different optical coating materials Optical absorption in coating leading to heating & deformation in substrate, surface Can trade against amount, complexity of thermal compensation; initial experimental verification near completion MLD (Oregon) pursuing a series of research coating runs targeting optical losses Sub-ppm losses (~0.5 ppm) observed in coatings from both MLD and from SMA Lyon Advanced LIGO G020243-00-D
17 Light source: Laser, Mode Cleaner Input Optics Modulator with RTA shows no evidence of thermal lensing at 50W RTA-based EOMs are currently being fabricated Demonstrated 45 dB attenuation and 98% TEM00 mode recovery with a thermally compensated Faraday Isolator design (-dn/dT materials) Pre-Stabilized Laser (PSL) Three groups pursuing alternate design approaches to a 100W demonstration Master Oscillator Power Amplifier (MOPA) [Stanford] Stable-unstable slab oscillator [Adelaide] Rod systems [Hannover] Concept down select Aug 2002 Advanced LIGO G020243-00-D 18 High Power Testing: Gingin Facility ACIGA progressing well with high power test facility at Gingin Test high power components (isolators, modulators, scaled thermal compensation system, etc.) in a systems test Explore high power effects on control length, alignment impulse upon locking Investigate the cold start optical coupling problem (e.g, pre-heat?) Compare experimental results with simulation (Melody, E2E)
Status: LIGO Lab delivering two characterized sapphire test masses and a prototype thermal compensation system The facility and a test plan are being prepared Advanced LIGO G020243-00-D 19 Development Plan R&D, distributed throughout LSC, well underway No showstoppers found yet! Integrated Systems Tests of all new aspects of design Seismic Isolation Test at Stanford ETF, LASTI; Pre-Stabilized Laser (PSL), Input Mode Cleaner, Suspensions at LASTI High power testing at ACIGA Gingin facility Configurations, Servo Control Electronics Testing at the GEO Glasgow 10m lab, and in the LIGO 40m Lab Major Research Equipment (MREFC) funding proposal, Fall 02 Could be in force by early 05 Fabrication, installation, commissioning of installable hardware May upgrade one observatory, then second system upon proof
of success; or all at once depending upon observations, network at that time, and technical readiness Advanced LIGO G020243-00-D 20 Schedule: Installation A variety of options, driven by availability of major funding, any observations in the interim, status of other observatories, technical progress Start with all systems tested, fabricated commissioning might go faster than anticipated Upper (Feb 11) and lower (Nov 07) bounds on when observing proposal MRE $ start 1st Obs 2nd Obs submission available install on-line on-line Options -1 0 1 2 3 4 Aug/2001 LSC Mar/2002 LSC both oservatories in parallel + purchase core optics early + parallel (or no) first article test at LASTI
A significant step forward Exciting astrophysical sensitivity Challenging but not unrealistic technical goals Advances the art in materials, mechanics, optics, lasers, servocontrols A tight and rich collaboration NSF-funded research International contributors Program planned to mesh with fabrication of interferometer components leading to installation of new detectors starting in 2006 or 2007 Lessons learned from initial LIGO Thorough testing at LSC facilities to minimize impact on LIGO observation Coordination with other networked detectors to ensure continuous global observation Advanced LIGO G020243-00-D 22
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