  A macroscopic characterization of fractals showing up a structural transition
from dense to multibranched growth is made using optical diffraction theory.
Such fractals are generated via the numerical solution of the 2D Poisson and
Biharmonic equations and are compared to more 'regular'irreversible clusters
such as diffusion limited and Laplacian aggregates. The optical diffraction
method enables to identify a decrease of the fractal dimension above the
structural point.
