  In strong field laser physics it is a common practice to use the high-order
harmonic cutoff to estimate the laser intensity of the pulse that generates the
harmonic radiation. Based on the semiclassical arguments it is possible to find
a direct relationship between the maximum value of the photon energy and the
laser intensity. This approach is only valid if the electric field driving HHG
is spatially homogenous. In laser-matter processes driven by plasmonics fields,
the enhanced fields present a spatial dependence that strongly modifies the
electron motion and consequently the laser driven phenomena. As a result, this
method should be revised in order to more realistically estimate the field. In
this work, we demonstrate how the inhomogeneity of the fields will effect this
estimation. Furthermore, by employing both quantum mechanical and classical
calculations, we show how one can obtain a better estimation for the intensity
of the enhanced field in plasmonic nanostructure.
