LIGO Document G1800300-v2

Inhibition of the Cryogenic Mechanical Loss in Thin Films by Thickness Reduction

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Through the amorphous multi-layer stacks of TiO2/SiO2, we
demonstrated that the cryogenic mechanical loss can be inhibited
beyond the prediction of the existing equation by reducing the film thickness. The cryogenic mechanical loss, mainly the loss of the SiO2 film, decreased and the loss peak shifted to lower temperature as the thickness decreased. We attributed the effect to the elimination of the long-range TLS transitions, i.e. transitions of groups of atoms larger than the film thickness, by the reduced film thickness. We propose a new HR coatings that has blocking layers in between the ultra thin SiO2 layers to replace the QW SiO2 in the conventional coatings.Same effect could occur in the H-layer as well.
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