Nanophononic thin-film filters and mirrors studied by picosecond ultrasonics

Abstract

Optimized acoustic phonon thin-film filters are studied by picosecond ultrasonics. A broadband mirror and a color filter based on aperiodic multilayers were optimized to work in the subterahertz range, and grown by molecular beam epitaxy. Time resolved differential optical reflectivity experiments were performed with pump and probe pulses incident on opposite sides of the substrate. We provide broadband transmission curves for the phonon devices. The results are in good agreement with standard transfer matrix method simulations. In addition, we analyze the effects of the free surface and the influence of an Al capping layer on the response of the aperiodic devices.