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

Abstract

The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nanodisks 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.

Femtosecond laser-induced optical anisotropy in a two-dimensional lattice of magnetic dots

“…As ξ < 1, the discrepancy between the experimental and theoretical values becomes even greater. This indicates that we are probably observing a higher harmonic of the acoustic wave, whereas the speed of sound on the silica interface appears to be modified by the Co nanodots load [20,59].…”

“…A conventional approach to studying arrays of nanoobjects deals with optical reflectivity [20,21] or nonlinear-optical conversion [22][23][24], allowing us to find such interesting phenomena as coherent control of optical transmission [25], enhancement of the up-conversion luminescence intensity [26], and periodicity-induced pulse splitting [27]. On the other hand, much less attention is drawn towards polarization effects which are capable of revealing the dynamics of the optical anisotropy induced by a fs laser pulse.…”

Finite element analysis of surface modes in phononic crystal waveguides

“…20,21 Periodic nanostructures are used to modify the properties of SAWs, perturbing the stress and velocity fields associated with SAW propagation. 22,23 The published studies show that the filling factor, the ratio of the slab thickness to the lattice period, and the height of the pillar are the key parameters for the existence of complete bandgaps. 24,25 When the substrate's surface acoustic modes strongly couple to the periodic overlayer, the SAW will evolve into a pseudo-SAW which is partially localized in the nanostructures and radiates mechanical energy into the substrate due to the scattering introduced by the periodic overlayer.…”

Optical generation of surface acoustic waves guided at the linear boundary between two thin films

“…Recently, laser-generated SAWs in patterned thin film microstructures comprised of different materials have also attracted attention. [3][4][5][6] This activity is stimulated by the proliferation of photoacoustic techniques in process control applications in silicon microelectronics, 7,8 where patterned thin film structures play a crucial role.…”