High-Frequency Surface Acoustic Wave Propagation in Nanostructures Characterized by Coherent Extreme Ultraviolet Beams

We study ultrahigh frequency surface acoustic wave propagation in nickel-on-sapphire nanostructures. We make use of high-order harmonic generation to obtain ultrafast, coherent, beams in the extreme ultraviolet (EUV) region of the spectrum. The short wavelengths $\sim $30 nm allow us to measure propagation dynamics of surface acoustic waves to frequencies of nearly 50 GHz, corresponding to wavelengths as short as 125 nm. We repeat the measurement on a sequence of nanostructured samples to quantify dispersion of surface acoustic waves in a nanostructure series for the first time [1]. These measurements are critical for accurate characterization of interfaces beneath very thin films using this technique. [1] M. E. Siemens, et al. Applied Physics Letters, 94(9):093103, 2009.