Inhomogeneous mechanical losses in micro-oscillators with high reflectivity coating

TL;DR

This paper investigates how inhomogeneous mechanical losses affect micro-oscillators with high-reflectivity coatings, proposing strategies to reduce these losses and validating models that improve design for low-noise, high-sensitivity applications.

Contribution

It introduces a method to reduce mechanical losses by limiting coated area and incorporating an isolation stage, validated through finite-element modeling and experimental data.

Findings

Reduced coating area lowers mechanical strain and energy loss.

Isolation stage effectively uncouples mirror dynamics from support.

Finite-element models accurately predict quality factors and frequencies.

Abstract

We characterize the mechanical quality factor of micro-oscillators covered by a highly reflective coating. We test an approach to the reduction of mechanical losses, that consists in limiting the size of the coated area to reduce the strain and the consequent energy loss in this highly dissipative component. Moreover, a mechanical isolation stage is incorporated in the device. The results are discussed on the basis of an analysis of homogeneous and non-homogeneous losses in the device and validated by a set of Finite-Element models. The contributions of thermoelastic dissipation and coating losses are separated and the measured quality factors are found in agreement with the calculated values, while the absence of unmodeled losses confirms that the isolation element integrated in the device efficiently uncouples the dynamics of the mirror from the support system. Also the resonant frequencies evaluated by Finite-Element models are in good agreement with the experimental data, and allow the estimation of the Young modulus of the coating. The models that we have developed and validated are important for the design of oscillating micro-mirrors with high quality factor and, consequently, low thermal noise. Such devices are useful in general for high sensitivity sensors, and in particular for experiments of quantum opto-mechanics.