  We present a Raman study of Ar(+)-bombarded graphene samples with increasing
ion doses. This allows us to have a controlled, increasing, amount of defects.
We find that the ratio between the D and G peak intensities for a given defect
density strongly depends on the laser excitation energy. We quantify this
effect and present a simple equation for the determination of the point defect
density in graphene via Raman spectroscopy for any visible excitation energy.
We note that, for all excitations, the D to G intensity ratio reaches a maximum
for an inter-defect distance ~3nm. Thus, a given ratio could correspond to two
different defect densities, above or below the maximum. The analysis of the G
peak width and its dispersion with excitation energy solves this ambiguity.
