Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics Christian Schwarz 15 th September Genoa 1 Investigation of mechanical losses of 3 rd generation gravitational wave detector materials Ch. Schwarz 1, S. Kroker 2, D. Heinert 1, A. Tünnermann 2, P. Seidel 1 1 Friedrich-Schiller-University Jena, Institute of Solid State Physics, Helmholtzweg 5, D Jena, Germany 2 Friedrich-Schiller-University Jena, Institute of Applied Physics, Albert-Einstein-Straße 15, D Jena, Germany DFG / SFB TR 7

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 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

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 3 Find and understand suitable materials for optics components Available materials: - silicon - calcium fluoride - crystalline quartz - fused silica

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 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

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 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

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 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 Heat equation with deformation … thermal conductivity (2 nd order tensor) … thermal expansion coefficient The equation can be solved using COMSOL or ANSYS

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 7 Anisotropic solution of the heat equation using COMSOL TED limits the mechanical Losses between 20 K and 120 K

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 8 New design of the cantilevers for better handling Fragile cantilever covered by a “thick” frame of the same material

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 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)

Friedrich-Schiller-University Jena Institute of Solid State Physics – Low Temperature Physics 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