Excess Mechanical Loss Associated with Dielectric Mirror Coatings on Test Masses in Interferometric Gravitational Wave Detectors

TL;DR

This paper investigates how dielectric mirror coatings increase mechanical loss in fused silica and sapphire test masses, affecting thermal noise in gravitational wave detectors.

Contribution

It provides measurements of excess mechanical loss due to dielectric coatings on fused silica and sapphire, and analyzes their impact on thermal noise in interferometric detectors.

Findings

Dielectric coatings increase mechanical loss in test masses.

Excess loss impacts the thermal noise floor.

Results inform future mirror material choices.

Abstract

Interferometric gravitational wave detectors use mirrors whose substrates are formed from materials of low intrinsic mechanical dissipation. The two most likely choices for the test masses in future advanced detectors are fused silica or sapphire. These test masses must be coated to form mirrors, highly reflecting at 1064nm. We have measured the excess mechanical losses associated with adding dielectric coatings to substrates of fused silica and calculate the effect of the excess loss on the thermal noise in an advanced interferometer.