Quasimodes of a chaotic elastic cavity with increasing local losses

TL;DR

This study measures and analyzes the transition of elastic resonances from real to complex states in a chaotic silicon wafer as local losses increase, revealing how absorption affects mode properties.

Contribution

It provides the first direct measurement of elastic quasimodes' complex field distributions and introduces a simple model linking mode complexness to line broadening.

Findings

Complexness parameter is proportional to non-homogeneous line broadening.

Transition from real to complex modes occurs with increasing local absorption.

Two-level model supports experimental observations.

Abstract

We report non-invasive measurements of the complex field of elastic quasimodes of a silicon wafer with chaotic shape. The amplitude and phase spatial distribution of the flexural modes are directly obtained by Fourier transform of time measurements. We investigate the crossover from real mode to complex-valued quasimode, when absorption is progressively increased on one edge of the wafer. The complexness parameter, which characterizes the degree to which a resonance state is complex-valued, is measured for non-overlapping resonances and is found to be proportional to the non-homogeneous contribution to the line broadening of the resonance. A simple two-level model based on the effective Hamiltonian formalism supports our experimental results.