Surface optomechanics: Calculating optically excited acoustical whispering gallery modes in microspheres

TL;DR

This paper calculates and analyzes surface acoustic whispering gallery modes in microspheres, revealing diverse vibrational types and their potential for environmental sensing, advancing understanding of optomechanical interactions.

Contribution

It provides a detailed theoretical calculation of surface acoustic modes in microspheres, including their structure, frequency, and dependence on mode parameters, which was previously unexplored.

Findings

Identified various surface vibration modes including longitudinal, transverse, and Rayleigh types.

Demonstrated how mode structure varies with azimuthal, radial, and polar mode orders.

Showed that some modes are localized near the surface, useful for sensing applications.

Abstract

Stimulated Brillouin scattering recently allowed experimental excitation of surface acoustic resonances in micro-devices, enabling vibration at rates in the range of 50 MHz to 12 GHz. The experimental availability of such mechanical whispering gallery modes in photonic-MEMS raises questions on their structure and spectral distribution. Here we calculate the form and frequency of such vibrational surface whispering gallery modes, revealing diverse types of surface vibrations including longitudinal, transverse, and Rayleigh-type deformations. We parametrically investigate these various modes by changing their orders in the azimuthal, radial, and polar directions to reveal different vibrational structures including mechanical resonances that are localized near the interface with the environment where they can sense changes in the surroundings.