  In a random laser (RL), a system possessing in itself both resonator and
amplifying medium while lacking of a macroscopic cavity, the feedback is
provided by the scattering, which forces light to travel across very long
random paths. Here we demonstrate that RL properties may be tuned by the
topology of the scattering system retaining unchanged scattering strength and
gain efficiency. This is possible in a system based on sparse clusters,
possessing two relevant structural lengths: the macroscopic inter cluster
separation and the mesoscopic intra-cluster mean free path.
