Thermo-mechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near infrared pump-probe diffraction experiments

TL;DR

This study investigates the ultrafast thermal and mechanical dynamics of metallic nano-disk arrays, demonstrating the excitation of surface acoustic waves and analyzing their interaction with the substrate using experiments and simulations.

Contribution

It provides new insights into the excitation and damping mechanisms of 2D surface acoustic waves in nano-disk arrays through combined experimental and numerical approaches.

Findings

2DSAW can be excited by ~120 fs laser pulses in nano-disk arrays.

The observed velocity shift is due to mechanical interaction between 2DSAWs and nano-disks.

Damping of 2DSAWs results from energy radiation into the substrate.

Abstract

The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nano-disks has been studied by near infrared pump-probe diffraction measurements, over a temporal range spanning from 100 fs to several nanoseconds. The experiments demonstrate that, in these systems, a two-dimensional surface acoustic wave (2DSAW), with a wavevector given by the reciprocal periodicity of the array, can be excited by ~120 fs Ti:sapphire laser pulses. In order to clarify the interaction between the nanodisks and the substrate, numerical calculations of the elastic eigenmodes and simulations of the thermodynamics of the system are developed through finite-element analysis. At this light, we unambiguously show that the observed 2DSAW velocity shift originates from the mechanical interaction between the 2DSAWs and the nano-disks, while the correlated 2DSAW damping is due to the energy radiation into the substrate.