  Brillouin light spectroscopy is a powerful and robust technique for measuring
the interfacial Dzyaloshinskii-Moriya interaction in thin films with broken
inversion symmetry. Here we show that the magnon visibility, i.e. the intensity
of the inelastically scattered light, strongly depends on the thickness of the
dielectric seed material - SiO$_2$. By using both, analytical thin-film optics
and numerical calculations, we reproduce the experimental data. We therefore
provide a guideline for the maximization of the signal by adapting the
substrate properties to the geometry of the measurement. Such a boost-up of the
signal eases the magnon visualization in ultrathin magnetic films, speeds-up
the measurement and increases the reliability of the data.
