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Study of optomechanical parametric instabilities in the Advanced Virgo detector

Abstract : On 14 September 2015, the LIGO-Virgo collaboration performed the very first direct detection of a gravitational wave, emitted from a binary black hole merger. This detection demonstrated the existence of black holes and that of the gravitational waves. It required to detect an exceptionally weak signal — the order of 10⁻²² Hz⁻½ in terms of strain amplitude. This tour de force was made possible thanks to several detector upgrades for over a decade. Increasing the laser power is a way to improve the sensitivity of interferometric gravitational wave detectors for it reduces even more the relative quantum shot noise at high frequency. However, optomechanical parametric instabilities can set a limit to that power. This thesis presents the simulations that we have performed to compute the parametric gain of each mechanical mode of the four suspended 3km-arm-cavity mirrors of Advanced Virgo during the Observing run O3 (04/2019--03/2020). We study the influence of mirror finite size effects, and deformation due to thermal absorption, on optical modes and parametric gains. Finally, this thesis also gives a prediction on the potential unstable mechanical modes in Advanced Virgo's configuration during the next Observing run O4, which is expected to start in mid-2022.
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Submitted on : Monday, June 14, 2021 - 1:59:08 PM
Last modification on : Thursday, July 1, 2021 - 4:46:48 PM


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  • HAL Id : tel-03259687, version 1


David Cohen. Study of optomechanical parametric instabilities in the Advanced Virgo detector. Astrophysics [astro-ph]. Université Paris-Saclay, 2021. English. ⟨NNT : 2021UPASP031⟩. ⟨tel-03259687⟩



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