Pushing the limits of acoustics at the nanoscale using femtosecond transient interferometry

摘要

Picosecond acoustics is the perfect technique for measuring elastic properties at nanoscale. But there still are some limitations to reach in-plane properties of ultra-thin films related to optical detection of ultra-high frequency surface acoustic waves. Here, we demonstrate that it is possible to push the limits of the technique using an interferometric detection instead of a usual reflectometry scheme. The experimental observations are supported by a simple model which explains from where comes the previous limitations and why it is possible to overcome it using the interferometric setup. Thanks to those results, it is possible to excite and detect very high frequency surface acoustic waves confined in ultra-thin layer using conventional femtosecond laser and optical setup.