نبذة مختصرة : International audience ; Picosecond acoustics allows for the probing of multilayered nanometric structures, with applications in various fields of fundamental research. In a recent study, Zhang et al.1 have reexamined the optical cavity effect that impacts time-domain Brillouin acoustic spectroscopy (TDBS) in such systems. This interference phenomenon arises from Fabry–Pérot cavities formed by the parallel interfaces within the stack. This has long been modeled either through a general solution based on Green’s functions or via analytical expressions derived from standard Fresnel formulas. In their study, Zhang et al. examined the Brillouin signal in a series of amorphous SiO2 layers grown on a Si wafer and capped with a metal Al transducer. This configuration had been thoroughly investigated as part of a larger effort to study high-frequency acoustic losses in silica glass by Ayrinhac et al. in Ref. 2. However, when attempting to reproduce these results, Zhang et al. failed to achieve quantitative agreement with the calculated expectations, due to poorly characterized samples and likely inadequate data processing. We show that simple optical reflectance measurements combined with appropriate data normalization can, in fact, fully account for such observations.
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