  We measure the angular divergence of a quasi-continuous, rf-outcoupled,
free-falling atom laser as a function of the outcoupling frequency. The data is
compared to a Gaussian-beam model of laser propagation that generalizes the
standard formalism of photonic lasers. Our treatment includes diffraction,
magnetic lensing, and interaction between the atom laser and the condensate. We
find that the dominant source of divergence is the condensate-laser
interaction.
