  We demonstrate a real-space imaging of a heterodyne signal of light that is
produced as a result of the Brillouin light scattering by coherently driven
magnons in magnetostatic modes. With this imaging technique, we characterize
surface magnetostatic modes (Damon-Eshbach modes) in a one-dimensional magnonic
crystal, which is formed by patterned aluminum strips deposited on the
ferromagnetic film. The modified band structures of the magnonic crystal are
deduced from the Fourier transforms of the real-space images. The heterodyne
imaging provides a simple and powerful method to probe magnons in structured
ferromagnetic films, paving a way to investigate more complex phenomena, such
as Anderson localization and topological transport with magnons.
