Fiber-integrated microcavities for efficient generation of coherent acoustic phonons

TL;DR

This paper presents fiber-integrated microcavities that enable stable, low-power generation and detection of coherent acoustic phonons, simplifying experimental setup and improving reproducibility for nanoscale acoustic studies.

Contribution

It introduces a fiber-integrated approach to microcavities that overcomes focalization challenges, allowing stable, reproducible phonon experiments without focusing optics.

Findings

Achieved at least 66% reflectivity contrast in samples.

Observed stable phonon signals over a full day.

Detected phonon signals at excitation powers as low as 1 μW.

Abstract

Coherent phonon generation by optical pump-probe experiments has enabled the study of acoustic properties at the nanoscale in planar heterostructures, plasmonic resonators, micropillars and nanowires. Focalizing both pump and probe on the same spot of the sample is a critical part of pump-probe experiments. This is particularly relevant in the case of small objects. The main practical challenges for the actual implementation of this technique are: stability of the spatio-temporal overlap, reproducibility of the focalization and optical mode matching conditions. In this work, we solve these three challenges for the case of planar and micropillar optophononic cavities. We integrate the studied samples to single mode fibers lifting the need for focusing optics to excite and detect coherent acoustic phonons. The resulting excellent reflectivity contrast of at least 66% achieved in our samples allows us to observe stable coherent phonon signals over at least a full day and signals at extremely low excitation powers of 1uW. The monolithic sample structure is transportable and could provide a means to perform reproducible plug-and-play experiments.