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Understanding Advanced Virgo noise
Michał W ˛ as
LAPP/IN2P3 - Annecy
Michał W ˛ as (LAPP) 2018 Jun 19 1 / 15
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Advanced Virgo full noise budget
Michał W ˛ as (LAPP) 2018 Jun 19 2 / 15
Understanding Advanced Virgo noise Micha W as LAPP/IN2P3 - Annecy - - PowerPoint PPT Presentation
Understanding Advanced Virgo noise Micha W as LAPP/IN2P3 - Annecy - - PowerPoint PPT Presentation
def Understanding Advanced Virgo noise Micha W as LAPP/IN2P3 - Annecy Micha W as (LAPP) 2018 Jun 19 1 / 15 def Advanced Virgo full noise budget Micha W as (LAPP) 2018 Jun 19 2 / 15 def Noise budget basics Usually
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Noise budget basics
Usually consider linear coupling noise contribution to strain = TFcoupling function × Snoise level Coupling function TFcoupling function
◮ modeled ◮ modeled with factors measured online - frequency noise (losses & assymetry) ◮ measured through noise injections - angular noise
Noise level Snoise level
◮ modeled - shot noise ◮ measured offline - DAC noise ◮ measured online with auxiliary channels - angular noise
Add in quadrature all the noise contributions
Michał W ˛ as (LAPP) 2018 Jun 19 3 / 15
SLIDE 4
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Building a complete interferometer model
Optickle model Suspension response & noise From PD to DOF From DOF to feedback Frequency and amplitude ad-hoc model An IMC model not used
Construct a simulink diagram of the interferometer Double pendulum to model suspensions Use simulation to compute optical response Include many degrees of freedom:
◮ DARM: differential arm length ◮ CARM: common arm length / laser frequency ◮ MICH: Michelson ◮ PRCL: power recycling cavity length Michał W ˛ as (LAPP) 2018 Jun 19 4 / 15
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ITF model → a rough calibration of DARM into h(t)
Matches well proper data calibration
Michał W ˛ as (LAPP) 2018 Jun 19 5 / 15
SLIDE 6
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Advanced Virgo full noise budget
Michał W ˛ as (LAPP) 2018 Jun 19 6 / 15
SLIDE 7
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Advanced Virgo main limitations
Michał W ˛ as (LAPP) 2018 Jun 19 7 / 15
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Demodulation phase noise - a bilinear coupling
Phase fluctuation I phase Q phase Projected noise
δI(t) = Q(t) × δφ(t) Large offset an issue ⇒ Uncontrolled degrees of freedom are an issue
Michał W ˛ as (LAPP) 2018 Jun 19 8 / 15
SLIDE 9
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Scattered light
300mW 300mW 300mW 70mW 13W
beam splitter photo-detector laser resonant cavity power recycling mirror mirrors 13 W 500 W 70 kW 3 km
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>90% of injected light lost inside the interferometer
◮ absorption in mirrors (causes thermal lensing) ◮ mirror imperfection ⇒ scattered light
⇒ put absorbing materials everywhere
Difficult, measure light phase with 10−12 precision
⇒ ∼ 1 photon per second in 100 kW
Michał W ˛ as (LAPP) 2018 Jun 19 9 / 15
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Scattered light - a non linear coupling
∼ 10% of light detected at various ports Non linear coupling of scattering surface motion x(t) n(t) = K sin 4π λ x(t)
- ◮ Move in a controlled way different benches to locate coupling
◮ In bad weather ground motion at 0.3Hz leads to noise up to 50Hz Michał W ˛ as (LAPP) 2018 Jun 19 10 / 15
SLIDE 11
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Brute force coherence to understand noise drifts
Observed wandering line Found correlation Track frequency of a moving line Correlate with slow monitoring, e.g. temperature Automated blind search on thousands of channels
Michał W ˛ as (LAPP) 2018 Jun 19 11 / 15
SLIDE 12
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GW sensitivity
smallest observable GW amplitude ∝ S(f) × S/Nthreshold Astrophysical triggers, GW models, etc ... changes search parameter space ⇒ S/Nthreshold depends on the search hypothesis
Michał W ˛ as (LAPP) 2018 Jun 19 12 / 15
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Modeled inspiral search
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X: 11 Y: 6.2e−05 X: 9.2 Y: 6.9 coherent SNR Rate [yr−1] inspiral Gaussian
For modeled search noise is close to Gaussian
Michał W ˛ as (LAPP) 2018 Jun 19 13 / 15
SLIDE 14
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Non stationary noise impact depends on GW search type
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X: 13 Y: 0.18 X: 8.3 Y: 32 coherent SNR Rate [yr−1] Gaussian inspiral burst >200Hz burst <200Hz
Unmodeled transient searches are more affected by transient noise
Michał W ˛ as (LAPP) 2018 Jun 19 14 / 15
SLIDE 15
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Summary
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X: 13 Y: 0.18 X: 8.3 Y: 32 coherent SNR Rate [yr−1] Gaussian inspiral burst >200Hz burst <200Hz
Both stationary spectrum and short transients limit detector sensitivity Global instrument simulations help understanding cross-coupling Shaking instrument in different ways allows to measure coupling Looking for time correlations helps finding origin of issues
Michał W ˛ as (LAPP) 2018 Jun 19 15 / 15