Thermal noise of gram-scale cantilever flexures

TL;DR

This paper measures thermal noise in niobium and aluminium flexures across a relevant frequency range for gravitational wave detectors, demonstrating a model that explains the interplay of structural and thermoelastic loss.

Contribution

It provides the first detailed measurements of thermal noise in these flexures in the audio frequency band relevant to gravitational wave detection.

Findings

Thermal noise measurements match the simple loss model.

Structural and thermoelastic loss both influence thermal noise.

Results inform quantum noise investigations in precision measurement.

Abstract

We present measurements of thermal noise in niobium and aluminium flexures. Our measurements cover the audio frequency band from 10Hz to 10kHz, which is of particular relevance to ground-based interferometric gravitational wave detectors, and span up to an order of magnitude above and below the fundamental flexure resonances at 50Hz - 300Hz. Our results are well-explained by a simple model in which both structural and thermoelastic loss play a role. The ability of such a model to explain this interplay is important for investigations of quantum-radiation-pressure noise and the standard quantum limit.