[en] We quantitatively study interfacial adhesion in a two-layer membrane system consisting of Al and Si with femtosecond time-resolved laser spectroscopy. High-frequency acoustic pulses in the sub-THz regime are utilized to characterize the membrane system. In order to explain the distinct features of the measured data, a spring model for the Al/Si interface is employed. We show that acoustic dissipation in this system needs to be included for accurate modeling of the interface adhesion over a broad frequency range. This modeling approach yields a spring constant of ${\mathrm{\eta <!--\; ??\; -->}}_{\mathrm{A}\mathrm{l}-<!--\; ???\; -->\mathrm{S}\mathrm{i}}=17$ $\mathrm{k}\mathrm{g}{\mathrm{n}\mathrm{m}}^{-<!--\; ???\; -->2}{\mathrm{s}}^{-<!--\; ???\; -->2}$, an acoustic phonon lifetime of ${\mathrm{\tau <!--\; ??\; -->}}_{\mathrm{A}\mathrm{l}}=68$ ps at 240 GHz in polycrystalline Al and a frequency dependence of the lifetime in Si $\propto <!--\; ???\; -->{\mathrm{\omega <!--\; ??\; -->}}^{-<!--\; ???\; -->1}$ in the frequency range from 50–800 GHz. (paper)