  We perform time-resolved exact diagonalization of the Hubbard model with time
dependent hoppings on small clusters of up to $12$ sites. Here, the time
dependence originates from a classic electromagnetic pulse, which mimics the
impact of a photon. We investigate the behavior of the double occupation and
spectral function after the pulse for different cluster geometries and on-site
potentials. We find impact ionization in all studied geometries except for
one-dimensional chains. Adding next-nearest neighbor hopping to the model leads
to a significant enhancement of impact ionization, as does disorder and
geometric frustration of a triangular lattice.
