  Coherent sub-THz phonons incident on a gold grating that is deposited on a
dielectric substrate undergo diffraction and thereby induce an alteration of
the surface plasmon-polariton resonance. This results in efficient
high-frequency modulation (up to 110 GHz) of the structure's reflectivity for
visible light in the vicinity of the plasmon-polariton resonance. High
modulation efficiency is achieved by designing a periodic nanostructure which
provides both plasmon-polariton and phonon resonances. Our theoretical analysis
shows that the dynamical alteration of the plasmon-polariton resonance is
governed by modulation of the slit widths within the grating at the frequencies
of higher-order phonon resonances.
