Sub-harmonic resonant excitation of confined acoustic modes at GHz frequencies with a high-repetition-rate femtosecond laser

TL;DR

This paper introduces a novel sub-harmonic resonant optical excitation method using femtosecond lasers to characterize high-frequency phononic and nanomechanical systems, enabling precise measurement of vibrational properties.

Contribution

It demonstrates the application of sub-harmonic resonant excitation for detailed characterization of confined acoustic modes in semiconductor membranes, achieving high-resolution measurements.

Findings

Amplified mechanical amplitude at sub-harmonic resonance

Linewidth measured with megahertz resolution

Vibrational state lifetime and quality factor determined

Abstract

We propose sub-harmonic resonant optical excitation with femtosecond lasers as a new method for the characterization of phononic and nanomechanical systems in the gigahertz to terahertz frequency range. This method is applied for the investigation of confined acoustic modes in a free-standing semiconductor membrane. By tuning the repetition rate of a femtosecond laser through a sub-harmonic of a mechanical resonance we amplify the mechanical amplitude, directly measure the linewidth with megahertz resolution, infer the lifetime of the coherently excited vibrational states, accurately determine the system's quality factor, and determine the amplitude of the mechanical motion with femtometer resolution.