Material loss angles from direct measurements of broadband thermal noise

TL;DR

This paper measures the material loss angles of key coating materials used in gravitational wave detectors through direct thermal noise measurements and introduces a predictive theory for amorphous glassy oxides.

Contribution

It provides the first direct measurements of coating thermal noise for these materials and proposes a predictive model aligning well with experimental data.

Findings

Measured loss angles for Silica, Tantala, and Ti-doped Tantala.

Developed a predictive theory for amorphous glassy oxide properties.

Validated the theory with experimental results.

Abstract

We estimate the loss angles of the materials currently used in the highly reflective test-mass coatings of interferometric detectors of gravitational waves, namely Silica, Tantala, and Ti-dop ed Tantala, from direct measurement of coating thermal noise in an optical interferometer testbench, the Caltech TNI. We also present a simple predictive theory for the material properties of amorphous glassy oxide mixtures, which gives results in good agreement with our measurements on Ti-doped Tantala. Alternative measure ment methods and results are reviewed, and some critical issues are discussed.