The Virgo Experiment Michele Punturo INFN Perugia 3rd VESF School on Gravitational Waves Build up the interferometer h 2 h 10 21 L L0 “Kilometric” detector L0 103 m L 10 18 m NS/NS collapse @ Virgo cluster Quadrupolar nature of the gravitational wave: •A Michelson interferometer seems a very appropriate detector Eout t E1 t E2 t E1 Ein E2 Ein cost k L1 t cost k L2 t 2 Interference term Eout L2 t L1 t L2 t L1 t cos t k 2 2 2 Ein cos - k 3rd VESF school - Michele Punturo Virgo … Build up the interferometer • Let suppose that TGW>>2L/c: 2 n P 2 n Pout t Pin cos 2 L ht in 1 cos 2 L ht laser 2 laser Pout t 2 nt Pin t 1 cos 2 L h t 2 t laser • The largest high vacuum system in Europe: – About 7000 m3 – 1.2 m diameter pipe @ 10-7mbar (H2 partial pressure) • Reduction of light fluctuation given by air flux – 7 long towers (9m long) with differential vacuum: • Usual 10-7 mbar vacuum in the upper part • 10-9 mbar in the lower part 3rd VESF school - Michele Punturo Virgo 3 Why a Fabry-Perot? • In a Michelson the sensitivity to an arm length difference L=h·L is given by the slope, in the gray fringe, of Mich t 2L rt c 4 Lopt 4 1 L h Laser rt ht Resonant cavity: I t I 0 e s rt t s P( x ) 0.5 r1r2 F , F 2 1 r1r2 0 t12 r2 e 2ikL rFP r1 1 r1r2 e 2ikL 0 /26 5 10 6 4 2 [rad] FP 8 F 2 F Mich Lopt Lopt laser 1 00 x 6 /2 5 10 FP100 FP25 Michelson 0 -2 -4 -0.10 3rd VESF school - Michele Punturo Virgo -0.05 0.00 L/ 0.05 0.10 4 6 Why power recycled? • The gray fringe working point is not the right choice: – The ITF is not a “Null Instrument”, that is the output is not null when the input is null: large DC – We want to operate in the dark fringe: no DC if zero input – What to do with the light wasted in the input port? Recycle it! Shot noise reduced by the recycling factor, but how to extract the GW signal if we work at the dark fringe, where laser Pout 0 L 3rd VESF school - Michele Punturo Virgo 5 Modulation-Demodulation • To operate in the dark fringe, but converting the FP in a linear instrument we need to adopt a modulation-demodulation scheme: – Pound-Drever technique EOM PBS /4 Ein t E0 cosct cos mod t E0 cosct cos cos mod t sin ct sin cos mod t E0 cosct sin ct cos mod t PHD LO Out E E E0 cos c t 0 sin c mod t 0 sin c mod t 2 3rd VESF school - Michele Punturo Virgo carrier 2 sidebands 6 …modulation-demodulation • The carrier is resonant in the cavity, but not the sidebands ( shift). Hence, the reflected beam is Erefl t E0 cos c t sin c t cos mod t • Let suppose that there is a GW signal that modulates the phase of the incoming field. Its effect is present only in the carrier, because it is resonant in the cavity Erefl t E0 cos c t GW t sin c t cos mod t E0 cos ct cos GW t sin ct sin GW t E0 sin ct cos mod t E0 cos ct cos GW t E0 cos mod t sin GW t sin ct • At the output of the interferometer, the photodiode reads the power, averaged over c, hence we must evaluate the square of • The mixed product term gives: sin GW t cos mod t GW t cos mod t • Demodulating the mod disappears and the output is proportional to the gravitational signal: – We build a linear null instrument 3rd VESF school - Michele Punturo Virgo 7 GW interferometer as a Double-Superheterodyne Receiver GW h(gw) Antenna ITF mechanical part Laser E(laser) Parametric L(gw) transducer E(lasergw) i(mod gw) Sig. Photodiode ITF optical part E(lasermod) Preamp RF Sig. Mixer L.O. V(gw) Out L.O. V(mod) L(mod) Pockel cell V(mod gw) V(mod) R.F. Oscillator mod 3rd VESF school - Michele Punturo Virgo Sig. = Signal L.O. = Local Oscillator 8 Virgo simplified Optical Scheme 140m 3km 3rd VESF school - Michele Punturo Virgo 9 The injection system: The Laser 20 W, Nd:YVO4 laser, two pumping diodes Injection locked to a 0.7 W Nd:YAG laser Required power stability: P/P~10-8 Hz-1/2 Required frequency stability: 10-6 Hz1/2 Mode Cleaner L = 143 m • • • • Diode pump Slave Nd:YVO4 Laser Injection bench 1W master laser Telescope ITF Nd:YAG =1.064 mm ULE monolithic 22 W slave laser Reference cavity 10 Gaussian beams • Until now we considered, for the light, the plane wave approximation • But the beam, coming from a laser, shows a finite size and a approximately gaussian shape • In effect the propagation law of an electromagnetic field in an homogeneous medium gives: 2 y 2 z i m n 1 w0 n e Emn x, y, z, t E0 m e wx wx wx ik • Where n are the Hermite-gaussian functions: n H n e y2 z2 2 Rx 2 2 H 0 1 H1 • w(x) represents the beam size: • • x 2 x 2 w02 1 2 w2 x w02 1 2 w0 x0 x 2 x02 R(x) represents the curvature radius of the beam: Rx x x and is defined by: tan x0 3rd VESF school - Michele Punturo Virgo e i kx t H 2 4 2 2 ... w0 Minimum beam waist 11 Transverse Modes 00 and 01 3rd VESF school - Michele Punturo Virgo 12 Transverse Modes 11 and 22 3rd VESF school - Michele Punturo Virgo 13 Fabry Perot as mode cleaner • The Fabry-Perot cavity is a resonator that can be tuned to select the desired resonant frequency • In fact, the resonance condition is defined by the request that the complete round trip phase delay of the light inside the cavity is a integer multiple of 2. L • Let suppose for simplicity: xM xM 2 2 1 • The resonance conditions becomes: k L L L L k m n 1 tan 1 p , m n 1 tan 1 2 2 2 x0 2 x0 mnp m n 1 1 L 2L p 2 tan 2 x0 3rd VESF school - Michele Punturo Virgo p 1,2,... 1 14 … FP as mode cleaner mnp m n 1 1 L 2L p 2 tan 2 x0 1 • If we want to select the gaussian mode 00, we choose the length of the cavity in such a way exists a p1 index satisfying the previous resonance condition: 00p1 resonant • The mode 00 is then transmitted by the cavity 3rd VESF school - Michele Punturo Virgo 15 Input Mode Cleaner • Mode cleaner cavity: filters laser noise, selects TEM00 mode Input beam inbeam Transm. beam Input mode-cleaner: curved mirror Refl. beam • Mode cleaner cavity: filters laser noise, select TEM00 mode outbeam refbeam Input mode-cleaner: dihedron 16 Output Optics • Light filtering: output mode cleaner, 3.6 cm long monolithic cavity • Light detection: InGaAs photodiodes, 3 mm diameter, 90% quantum efficiency • Suppression of TEM01 by a factor of 10 • Length control via temperature (Peltier cell) 3rd VESF school - Michele Punturo Virgo Detection bench 17 Output Mode-Cleaner OMC filtering effect before OMC after OMC 3rd VESF school - Michele Punturo Virgo 18 Seismic Noise • The correct and usual way to realize an interferometer in an University Lab is to rigidly clamp the optics to the table • We cannot adopt this solution, mainly, because of the seismic f 0.1Hz A noise: x (f) m Hz , seism A 10 7 f2 xseism ( f ) xGW f f 105 Hz x • The simplest seismic filter is an harmonic oscillator, for frequencies larger than the resonant one: x x xseism 0 ~ x 2 0 02 ~ xseism 02 2 xseism • A pendulum is an harmonic oscillator of natural frequency: f0 1 2 g L • A cascade of N pendulums is a multistage filter whose transfer 2N function is: ~ f0 x 19 ~ xseism f Virgo “Superattenuators” XYZ pendulum chains to reduce seismic motion by a factor 1014 above 10 Hz Magnetic anti-springs Blades 20 Passive Isolation performance • Expected seismic displacement of the mirror (TF measured stage by stage): • Thermal noise is dominant above 4 Hz Isolation sufficient also for “advanced” interferometers • 2 ~ f0 x f 2 ~ xseism f f 2 f 2 i f 0 0 Q ~ x f0 N Q ~ xseism f 0 N Residual motion too high at the resonances (tens of microns): could be a problem for the ITF operation 3rd VESF school - Michele Punturo need of damping! Virgo 21 Working conditions • A FP is mainly a non-linear device. It can be used only at resonance where it is sensitive and linear: Pr_B8_DC -5 1.8 x 10 1.6 1.4 Power [W] 1.2 1 0.8 0.6 • Keep the main cavity locked to enhance the phase response 0.4 0.2 0 0 1 2 3 4 5 Samples (@20kHz) 6 7 8 4 4 seconds x 10 3rd VESF school - Michele Punturo Virgo 22 … working conditions 2 • The power recycling cavity must be kept locked to reduce the shot noise • Keep the ITF in the dark fringe to reduce the dependence on the power fluctuation 3rd VESF school - Michele Punturo Virgo 23 Interferometer Control • To push the ITF in the working conditions we need to know the status of the cavities • Mainly, we need to know 4 length and the angles of the mirrors respect to the beams • • Photodiodes Bx provide the error signals to control the 4 independent length of the interferometer Quadrant photodiodes provide the error signals to control the angular positions of the mirrors 3rd VESF school - Michele Punturo Virgo 24 Locking a cavity NI NE BS correction B7 B1p error NE correction B7 (Cavitypower) Locking trials Locked 3rd VESF school - Michele Punturo Virgo 25 Locking the ITF B8_phase/B8_DC West arm Michelson B5 B2 B1_quad North arm B5_phase/B7_DC 3rd VESF school - Michele Punturo Virgo 26 How the correction is applied? • Three application points – Top of the inverted pendulum (Filter 0) – Marionette – Mirror DC-0.01 Hz • Locking requirement: L 10-12 m • Tidal strain over 3 km: L 10-4 m • Resonant motions of the mirrors 0.01-8 Hz L 10-4 m 8-50 Hz Need to control the mirror position in a large range of frequency and displacement: •Need of hierarchical control 3rd VESF school - Michele Punturo Virgo 27 Mirror Actuators 3rd VESF school - Michele Punturo Virgo 28 Tides • Tides stretch Virgo arms up to 200 mm in 6 hours • The coils at the mirror level can support up to 10V corresponding to 100 mm displacement – The tide displacement causes a saturation of the coil voltage and a consequent delock of the ITF Tide prediction cavity power Coil voltage Tide effect saturation Loss of lock 29 Tide compensation • Example of hierarchical strategy: – The mirror level coil drivers haven’t enough dynamical range to compensate the tidal effect – This effect is very low frequency – Moving the inverted pendulum (IP) is easy and soft – Use the low frequency part of the interferometer signal as error signal 3rd VESF school - Michele Punturo Virgo 30 Designing the detector sensitivity ~ f 02 x ~ xseism f 2 f 2 i f 02 0 Q • Best seismic damping with low Q suspension • But not all the stages can be highly dissipative because of the suspension thermal noise • The ITF mirrors are suspended by an oscillator (the pendulum) that vibrates (Brownian motion) because of its finite temperature • The mirror mass itself is a system of oscillators (internal modes) that oscillate because T>0 • How to evaluate the thermal noise contribution? • You surely know the Nyquist theorem that defines the voltage noise at the end of a resistor of impedance R: V 4kBT R • Translating the electrical impedance into mechanical one we have the fluctuationdissipation 2theorem: Ftherm 4k BT Z 31 N Fluctuation-Dissipation theorem • The previous formulation of the FD theorem is equivalent to: 2 xtherm 4 k BT 2 Y where Y 1 Z • Introducing the transfer function of a mechanical system H(): x 4k T F 2 xtherm B H F F Z x i x H • For an harmonic oscillator: 2 therm x 4k BT 02 m 02 2 2 02 2 4k BT 02 5 0 m ; Q 0 • Thermal noise issues require mechanical Q as high as possible 3rd VESF school - Michele Punturo Virgo 1 32 L3 Special feature of a Pendulum • A pendulum is an harmonic oscillator where the restoring force is mainly given by the gravitation (lossless force). The dissipation is, instead, due to the elastic force of the suspension wire. k P k P 1 i P y k P k grav kel k grav kel 1 iw L2 L1 P Qy Qz kelw k el w kP k grav 1 P 2 Lw EI w n mg mg EI n 2 L2w 1 mg w n Lw I 4 •Very thin (and strong) suspension wires •Low loss steel wires Qx x z 33 r4 Contribution to the pendulum Q • The loss angle that enters in the thermal noise formula is not only due to the “intrinsic” material loss, but other excess losses must be taken in account: – Clamping losses – Frictional losses / eddy currents – Residual gas losses 3rd VESF school - Michele Punturo Virgo 34 Mirror thermal Noise • In the modal expansion approximation we can consider the Virgo mirrors as composed by an infinite number of oscillators. • In the limit <<1 the thermal noise displacement power spectrum is given by: 1 x 4k BT i 1 M ii2 • A better estimation of that power spectrum can be obtained by a direct application of the FD theorem (Levin et al.): 2 x 8k BT U wbeam ,... 2 • Where U is the strain energy in the mirror due to a static pressure having the distribution of the beam profile • Other dissipation should be taken in account: – – – – Coatings Thermo-elastic effects Excess losses due to the clamping and control system 3rd VESF school - Michele Punturo … Virgo 35 Virgo Mirrors • The Virgo mirrors are the largest (and more expensive) mirrors in the current GW detectors • Since the substrate specifications are very stringent a special fused silica (Suprasil 311 SV) have been realized on purpose for Virgo: – Low absorption: 0.7 ppm/cm – Low OH content (<< 50ppm) – Low birefringence (<5·10-4 rad/cm) • The coating specifications are still more stringent • @1064nm the nominal absorption should be about 1 ppm • The scattering should be lower than 5ppm • As usual the effective realization is more difficult than expected: • Excess optical losses in the mounted mirrors (pollution?) • Thermal effects 3rd VESF school - Michele Punturo Virgo 36 350 mm 100 mm 3rd VESF school - Michele Punturo Virgo 37 Optical read-out noise • Optical read-out noise is the (incoherent) sum of the shot noise and radiation pressure • In the current ITFs only the shot noise plays a relevant role, but it is instructive to see a formalism (KLMTV) that reports the two noises in a single expression: hor hSQL 2 1 Shot noise Radiation pressure 4 PBS 2 FP 2 PSQL FP 2 2 PSQL 4 M m L2arm FP 4 2 c FP 2 f knee 2 PBS is the power impinging the beam splitter: PBS Plaser Recycling 3rd VESF school - Michele Punturo Virgo hSQL c 4 Larm F 8 M m 2 L2arm 38 Virgo Nominal Sensitivity -18 10 (a) Seismic noise (b) Thermal pendulum (c) Thermal Mirror (d) Optical Read-Out (e) Newtonian noise (f) Nominal Virgo (b) -19 h(f) [1/sqrt(Hz)] 10 -20 10 (a) (f) -21 10 (e) (c) -22 10 (f) (d) -23 10 1 10 100 1000 10000 Frequency [Hz] 3rd VESF school - Michele Punturo Virgo 39 The real life! • The design of a GW interferometric detector is an hard job, but the attainment of the design sensitivity is even harder • In fact, a GW detector is a complex machine that needs a deep tuning of many parameters – Methods and technologies are completely new – 5 years of commissioning needed in LIGO – Similar time spent in Virgo 3rd VESF school - Michele Punturo Virgo 40 Commissioning evolution Phase A: Commissioning of interferometer arms • Test all aspects of control systems with a simple optical configuration - locking, automatic alignment, second stage of frequency stabilization and suspension hierarchical control (tidal and marionette) • First shake of the sub-systems 3rd VESF school - Michele Punturo Virgo 41 Commissioning evolution Phase A: Commissioning of interferometer arms • Test all aspects of control systems with a simple optical configuration - locking, automatic alignment, second stage of frequency stabilization and suspension hierarchical control (tidal and marionette) • First shake of the sub-systems 3rd VESF school - Michele Punturo Virgo 42 Commissioning evolution Phase A: Commissioning of interferometer arms • Test all aspects of control systems with a simple optical configuration - locking, automatic alignment, second stage of frequency stabilization and suspension hierarchical control (tidal and marionette) • First shake of the sub-systems Phase B: Commissioning of interferometer in ‘recombined mode’ • Useful intermediate step towards full interferometer lock • Verify functioning of BS longitudinal control • Re-run all aspects of control system in a more complex configuration • Start noise investigations 3rd VESF school - Michele Punturo Virgo 43 Commissioning evolution Phase A: Commissioning of interferometer arms • Test all aspects of control systems with a simple optical configuration - locking, automatic alignment, second stage of frequency stabilization and suspension hierarchical control (tidal and marionette) • First shake of the sub-systems Phase B: Commissioning of interferometer in ‘recombined mode’ • Useful intermediate step towards full interferometer lock • Verify functioning of BS longitudinal control • Re-run all aspects of control system in a more complex configuration • Start noise investigations Phase C: Commissioning of Recycled Fabry-Perot interferometer • Run full locking acquisition process • Verify functioning of PR mirror longitudinal control • Re-run SSFS, tidal control and marionette control • Implement complete wave-front sensing control • Continue noise investigations 3rd VESF school - Michele Punturo Virgo 44 Commissioning evolution Phase A: Commissioning of interferometer arms • Test all aspects of control systems with a simple optical configuration - locking, automatic alignment, second stage of frequency stabilization and suspension hierarchical control (tidal and marionette) • First shake of the sub-systems Phase B: Commissioning of interferometer in ‘recombined mode’ • Useful intermediate step towards full interferometer lock • Verify functioning of BS longitudinal control • Re-run all aspects of control system in a more complex configuration • Start noise investigations Phase C: Commissioning of Recycled Fabry-Perot interferometer • Run full locking acquisition process • Verify functioning of PR mirror longitudinal control • Re-run SSFS, tidal control and marionette control • Implement complete wave-front sensing control • Continue noise investigations Phase D: Noise hunting 3rd VESF school - Michele Punturo Virgo 45 Sensitivity Improvement 3rd VESF school - Michele Punturo Virgo 46 Sensitivity of the global network NSNS detection distance 3rd VESF school - Michele Punturo ~6Mpc Virgo 47 Noise Budget Unclear excess noise sources Residual light scattering Shot noise dominated 48 Scientific case: Thermal effects in the Virgo mirrors • The 3km Virgo arms are a long Fabry Perot cavity: LM LA AR HR ~10-3 – 10-4 • Hence, actually, each arm is a double FP cavity: 2 rHRe 2ikL • Etalon effect r r t AR M M AR 1 rAR rHRe 2ikLM 3rd VESF school - Michele Punturo Virgo tM2 rend e 2ikLA rFP rM 1 rM rend e 2ikLA 49 Etalon Effect • Hence, the Finesse of the cavity and all the fundamental parameters of the ITF are affected by the input mirror optical thickness variation • But, why the mirror optical thickness fluctuates? • Temperature!! 2 d 2 dn dx kx n x dT T xn T dT dT 2 dn x (n 1) T dT • Hence, knowing the mirror temperature it is possible to predict some of the ITF performances • OK, but how to measure the mirror temperature? 3rd VESF school - Michele Punturo Virgo 50 Resonant mode technique • Obviously the resonant frequencies of a body depend on the temperature of the body • For a Virgo mirror we evaluated this dependence with a ANSYS based FEM Frequency Variation [Hz] 5 4 3 2 1 Drum mode: 0.61 Hz/K ButterxM ButtertM DrumM 0 -1 -2 -3 Butterfly mode(s): 0.28 Hz/K -4 282 284 286 288 290 292 294 296 298 300 302 Temperature [K] 51 Calibration crosscheck 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 -0,9 -1,0 -1,1 -1,2 -1,3 dTWIn WIoven Scientific run 30 days 23,8 23,7 23,6 23,5 23,4 23,3 23,2 23,1 23,0 22,9 22,8 22,7 22,6 22,5 22,4 22,3 22,2 22,1 22,0 21,9 T [C] T resonant mode [K] • To crosscheck the FEM calibration we compared the prediction with the temperature measured just outside the towers 000 000 000 000 000 000 728 320 912 504 096 688 5 8 0 3 6 8 6 6 7 7 7 7 8 8 8 8 8 8 Time [GPStime] 52 Evidence of the Etalon effect • The confidence in the resonant mode is critical in this evaluation. – Could we find an independent confirmation? • Etalon effect in the input mirrors AR HR HR B7/B8 phd LB r2 dn dT r3 0 0 AR coating LA 0.02 P/P r1 varPot ( x) 0.04 0.06 0.067846 0.08 0 0 0.2 0.4 0.6 x T 0.8 53 1 1 VSR1 BNS horizon • During the VSR1 the horizon grown from 3.7 to 4 Mpc thanks to the limited commissioning activity – Now we are at about 6Mpc • The fluctuation in the horizon was caused by – Bad weather – Alignment fluctuation – Etalon effect combined with control issues 3rd VESF school - Michele Punturo Virgo 54 The dark side of the experiment! • The photodiode that contains the GW signal is “just one”. • We are sensible up to few kHz: – A sampling rate of 20kHz is “correctly oversized” – 20kHz 8Bytes = 160kB/s of expected data recording • Instead we write about 7-8MB/s…… why? • Many control channels: – Secondary beams – Actuation and error signals – Environmental monitoring N I W I B S S R D B P R Temperature probes, 88, 1 Hz Episensors, 6, 1 kHz Humidity probes, 4, 1 Hz Accelerometers, 9, 10 kHz Pressure probes, 4, 1 Hz Magnetometers, 3, 20 kHz Microphones, 3, 10 kHz I B B 55 The online architecture Front-End Data Collection Fast Digitization , Environment Local Servo-Loop Monitoring Fast Digitization Locking and Alignment Servo-Loops Photodiodes Readout Global Control Damping and Control suspensions Calibration Frame Builder, Local Control Slow Monitoring Station GPS Timing Crate Fast Frame Builder Main Frame Builder Detector Monitoring Timing System Slow Frame Builder Frame Building Frame Processing Data GPS signals Archiving Timing Information Servo-Loop DOL (Optical Fibers) DOL (Optical Fibers) SMS format (Ethernet) Frame format (Ethernet) H Reconstruction 3rd VESF school - Michele Punturo Virgo Data Quality On-line Processing Offline data analysis 56 The evolution • Virgo concluded its first long run (VSR1) in parallel with the LIGO-S5 run the 1st of October 2007 • During the winter we had an intense commissioning and upgrade activity that reduced the noise level mainly at low frequency and improved our sensitivity and detector understanding • In the next summer a long shutdown is scheduled to install a powerful laser (reduction of the shot noise), an improved injection optical system and new control and DAQ electronics Virgo+ project 3rd VESF school - Michele Punturo Virgo 57 Detection Probability • The Initial LIGO and Virgo detectors are often called 1st generation ITF detectors • What is the detection probability with them? – It depends by the typical merger rate in a galaxy times the number of galaxies “visible” by our detector – The merger rate is quite uncertain (CBC group) Source NS-NS (MWEG-1 Myr-1) Rmin Rre Rpl Rup 0.1 100 1000 2000 Hence the detection rate is not well defined (but low!): Source NS-NS initial LIGO (yr-1) Rmin Rre Rpl Rup 1.5×10-5 0.015 0.15 0.3 Abbreviation Rate statement Physical significance Up Upper limit Rates should be no higher than … Pl Plausible optimistic estimate Rates could be as high as Re Realistic estimate Min Rates are likely to be 3rd VESF school - Michele Punturo Expected minimal estimate Virgo Rates should be at least 58 Let suppose that the distribution of the galaxies in the universe is uniform: Basic Idea R 3 Nevents Vdetectionsphere Rdetection Increasing the detection distance by 2 (10), a factor 8 (1000) in event rate could be expected In effect the galaxies density is not constant: Credit: R.Powell 3rd VESF school - Michele Punturo Virgo 59 Detector Evolution program • Current detectors: – 1st generation: Virgo & LIGO • <15MPc • Enhanced detectors: – 1.5 generation: • Virgo+ & enhanced LIGO – 20-40 MPc • Advanced detectors: – 2nd generation: • Advanced Virgo & Advanced LIGO LIGO - Virgo LIGO+ - Virgo+ Credit: R.Powell – ~150 MPc – 3rd generation: • E.T. FP7 Design Study – ??? MPc 3rd VESF school - Michele Punturo Virgo AdvLIGO - AdvVirgo 60 Detector evolution timeline ´06 ´07 ´08 ´09 ´10 ´11 ´12 ´13 ´14 ´15 ´16 ´17 ´18 ´19 ´20 ´21 ´22 Virgo+ Virgo GEO HF GEO LIGO Advanced Virgo Hanford Livingston LIGO+ Advanced LIGO Launch LISA E.T. DS PCP Construction 3rd VESF school - Michele Punturo Virgo Transfer data Commissioning data 61 Key points of the advanced detectors • Reduction of the shot noise: – – – – Higher laser power (160W laser) Higher cavity finesse DC detection Signal recycling • Reduction of the mirror thermal noise – – – – Improved materials for the substrates Heavier substrates Improved coatings materials and geometries Improved beam geometries (Virgo) • Reduction of the suspension thermal noise – Monolithic fused silica suspensions • Reduction of seismic noise – Active suspensions (LIGO) 3rd VESF school - Michele Punturo Virgo 62 Sensitivity evolution 10 -18 h(f) [1/sqrt(Hz)] st 10 -19 10 -20 10 -21 10 -22 10 -23 10 -24 1 generation: Virgo LIGO 1.5 generation: Virgo+ eLIGO nd 2 generation advVirgo advLIGO 10 100 1000 10000 Frequency [Hz] 3rd VESF school - Michele Punturo Virgo 63 rd 3 generation: ET • Advanced detectors are an evolution “in situ” of the current detectors • To gain a further factor 10 in sensitivity the current infrastructures are insufficient • We need: – Underground sites • Reduction of the seismic and Newtonian noise – Cryogenic infrastructures • Reduction of the thermal noise and of the optics lensing • GEO and Virgo collaborators started, with the European Commission support, a design study of a 3rd generation GW observatory: ET 3rd VESF school - Michele Punturo Virgo 64 3rd VESF school - Michele Punturo Virgo 65