Low Thermal Noise Coating for New Generation Gravitational-Wave Detectors

Abstract : The work of this thesis is the study of mechanical and optical properties of coatings (mainly deposited by IBS technique at LMA), with the purpose of finding a new possible material with the aim of reduce the coating thermal noise in current and in future gravitational-wave detectors (GWDs). The mechanical characterization done at LMA regards measurements of internal friction and elastic constants by the ring-down method using a Gentle Nodal Suspension (GeNS) system. The optical characterization has been done using spectroscopic ellipsometry (SE). Thanks to a collaboration with the OPTMATLAB of the University of Genova, I was able to characterize the samples using SE in a wide-range energy region (from UV to NIR). The first analysed samples are the coatings currently used in GWDs, SiO2, Ta2O5 and Ti:Ta2O5. Then, Nb2O5, Nb:TiO2, Zr:Ta2O5, SiC and SiNx have been characterize as high-refractive index coatings, whereas MgF2 and AlF3 have been studied with the purpose of replace the low-refractive index, reducing the total coating thickness, hence the coating thermal noise. Among the investigated coatings, Zr:Ta2O5 and SiNx provided the most promising results in term of internal friction. Important finding have been achieved regarding the theory of the internal friction of amorphous oxides and the optical and mechanical characterization of the samples
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Alex Amato. Low Thermal Noise Coating for New Generation Gravitational-Wave Detectors. Material chemistry. Université de Lyon, 2019. English. ⟨NNT : 2019LYSE1245⟩. ⟨tel-02475821⟩

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