Résumé
Finite sample sizes increase the measured Brillouin scattering linewidths. This should not be mistaken for a genuine damping of sound. Using high-resolution interferometry, we show that in silica glass under ambient conditions and with visible light excitation, the additional width becomes observable for sample thicknesses below 0.2 mm. Similarly, light absorption reduces the scattering volume, producing a strong contribution to the width for excitation of bulk samples above their absorption edge. The resulting limitations are illustrated for UV Brillouin scattering from silica.