  Highly confined vectorial electromagnetic field distributions represent an
excellent tool for detailed studies in nano-optics and high resolution
microscopy, such as nonlinear microscopy, advanced fluorescence imaging or
nanoplasmonics. Such field distributions can be generated, for instance, by
tight focussing of polarized light beams. To guarantee high quality and
resolution in the investigation of objects with sub-wavelength dimensions, the
precise knowledge of the spatial distribution of the exciting vectorial field
is of utmost importance. Full-field reconstruction methods presented so far
involved, for instance, complex near-field techniques. Here, we demonstrate a
simple and straight-forward to implement measurement scheme and reconstruction
algorithm based on the scattering signal of a single spherical nanoparticle as
a field-probe. We are able to reconstruct the amplitudes of the individual
focal field components as well as their relative phase distributions with
sub-wavelength resolution from a single scan measurement without the need for
polarization analysis of the scattered light. This scheme can help to improve
modern microscopy and nanoscopy techniques.
