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Investigation of mechanical losses of 3 rd generation gravitational wave detector materials

This study aims to investigate mechanical losses in third-generation gravitational wave detector materials, specifically focusing on cryogenic techniques to reduce thermal noise and find low mechanical loss materials for optics components. The study also explores suspension materials and geometries with optimal thermal properties to achieve the required low temperatures and noise budget. Silicon is identified as the most promising material, but further measurements and analysis are needed to understand its performance at specific temperatures. The research also emphasizes the importance of knowledge about thermoelastic damping (TED) in predicting and limiting mechanical losses in the targeted temperature range. Anisotropic solutions of heat equation using COMSOL are utilized for calculating TED and improving cantilever designs. The future work includes supporting WP2 with experimental data, investigating phonon-phonon interactions at low temperatures, and calculating TED for defined geometries.

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Investigation of mechanical losses of 3 rd generation gravitational wave detector materials

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  1. Investigation of mechanical losses of 3rd generation gravitational wave detector materials Ch. Schwarz1, S. Kroker2, D. Heinert1, A. Tünnermann2, P. Seidel1 1Friedrich-Schiller-University Jena, Institute of Solid State Physics, Helmholtzweg 5, D-07743 Jena, Germany 2Friedrich-Schiller-University Jena, Institute of Applied Physics, Albert-Einstein-Straße 15, D-07745 Jena, Germany DFG / SFB TR 7

  2. Aim for WP2: • Use of cryogenic techniques to reduce thermal noise • find and understand low mechanical loss materials for optics components • (thermo elastic damping & phonon-phonon interaction) • suspension materials and geometries with best available thermal • properties (e.g. conductivity) to reach required low temperatures and noise • budget

  3. Find and understand suitable materials for optics components • Available materials: • silicon • calcium fluoride • crystalline quartz • fused silica

  4. Most promising material: silicon - several publications about silicon (e.g. McGuigan et al.) show dips in the Q-factor around 120K and 18K > No measurements done in Jena showed dips at these temperatures

  5. Loss measurements of silicon cantilevers (as suspension elements in ET) in a frequency range between 25 Hz and 250 kHz The lowest mechanical loss measured was limited by TED between 50 K and 300 K

  6. Why is the knowledge about TED so important? - Depending on several parameters ( , , …) TED limits the mechanical losses between 100 and 18K > for a prediction of TED for a defined (ET mirror, suspension) geometry it’s necessary to solve the … thermal conductivity (2nd order tensor) Heat equation with deformation … thermal expansion coefficient The equation can be solved using COMSOL or ANSYS

  7. Anisotropic solution of the heat equation using COMSOL TED limits the mechanical Losses between 20 K and 120 K

  8. New design of the cantilevers for better handling Fragile cantilever covered by a “thick” frame of the same material

  9. Measurement of thermal conductivity - exact values for of available silicon samples for mechanical loss measurements - geometry dependence of for cryogenic suspension elements (e.g. silicon cantilever as plate spring)

  10. Future: - support of WP2 with experimental data of mechanical loss measurements and thermal conductivity - Further investigations of the phonon-phonon interactions at low temperatures using experimental data of thermal conductivity - calculation of TED for defined geometries

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