title: Probing thermomechanics at the nanoscale: impulsively excited pseudosurface acoustic waves in hypersonic phononic crystals.
abstract: High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system's initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system's excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths.
authors.affiliation: JILA, University of Colorado at Boulder , Boulder, Colorado 80309, United States. dnardi@dmf.unicatt.it
authors.forename: Damiano
authors.initials: D
authors.lastname: Nardi
authors.forename: Marco
authors.initials: M
authors.lastname: Travagliati
authors.forename: Mark E
authors.initials: ME
authors.lastname: Siemens
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Murnane
authors.forename: Henry C
authors.initials: HC
authors.lastname: Kapteyn
authors.forename: Gabriele
authors.initials: G
authors.lastname: Ferrini
authors.forename: Fulvio
authors.initials: F
authors.lastname: Parmigiani
authors.forename: Francesco
authors.initials: F
authors.lastname: Banfi